Kamaruddin, I.S. (2011). Diversity and feeding guilds of fish populations in Pengkalan Gawi - Pulau Dula section of Tasik Kenyir Terengganu, Malaysia. Master of science thesis. Universiti Putra Malaysia. 94p.
The need for hydroelectric power, irrigation, flood mitigation, drinking water and recreational opportunities has led to the construction of many reservoirs. According to Yusoff et al. (1995), most reservoirs were constructed for non-fisheries purposes but many of them contribute to food as well as recreational fisheries. In Malaysia, there are 63 large reservoirs with a total storage of 25 billion m3 ranging in size from 10 ha for Mahang Reservoir to 37,000 ha for the Kenyir Reservoir (Makhlough, 2008).
Dams and reservoirs in Malaysia which are constantly increasing in numbers play an important role not only in electric and water supply but also in providing a source of fish to the local community, sustainable aquaculture and maintenance of fish diversity. The aborigine depends on the freshwater fishes as their main source of protein and the local people depend on the lakes for their livelihood by fishing and servicing tourists. Thus, the initiation of reservoir fisheries could offer a significant contribution to fish production and socioeconomic development of local communities (De Silva and Davy, 2009).
Tasik Kenyir (Lake Kenyir) is one of the aquatic ecosystems that can be found in Malaysia, is actually a reservoir that was inundated due to the dam construction for hydroelectric power. Since its inundation, Tasik Kenyir has generated various socio-economic activities for the local people and recreational fishing activities for the tourists, and is known as a paradise for anglers. Tasik Kenyir is an important source of freshwater fish where major fish species landed are tinfoil barb (Lampam Sungai), Barbodes schwanenfeldii, Hampala barb (Sebarau), Hampala macrolepidota, river catfish (Baung), Hemibagrus nemurus, and giant snakehead (Toman), Channa micropeltes.
However, the freshwater fish catch in Tasik Kenyir have declined over the past few years. Jackson and Marmulla (2001) reported that an annual catch of 720 metric tonnes of fish in Tasik Kenyir. This figure was calculated based on Yusoff et al. (1995) findings which has reported a yield of 20 kg/ha/year. This figure however declined in 2007 where the estimated fish production as reported by the Department of Fisheries Malaysia was only 105.13 metric tonnes.
It is believed that over exploitation and habitat degradation have depleted the fish stocks in the reservoir. Excessive exploitations by the local community as food sources might affect the composition of fish population in the lake and resulted in overfishing. The numbers of fish within many major species have been reduced by the use of gill nets, cast net and fish traps by these people in Tasik Kenyir. The depletion in fish stock has also been linked by the destruction of fish habitat. Pressure in the water catchment area such as development of tourism activities, logging activities and land degradation from plantation agriculture resulted in siltation and pollution which effect fish habitat and biodiversity looses.
Hence, a concerted effort in Tasik Kenyir is required in order to maintain the fish sources at a sustainable level. Study on the biology of fishes is important in providing information on the management and conservation programmes. Study on fish species diversity and their feeding habits are needed to characterise present status of the Tasik Kenyir fishery. In addition, detailed and comprehensive studies on the fish population in Tasik Kenyir are still lacking. It is partly for this reason that we are inspired to conduct the current study on Pengkalan Gawi – Pulau Dula section in Tasik Kenyir so as to determine the current conditions of the lake.
The findings from this study are expected to provide some useful inputs for fishery management in the lake. Maybe in the future Tasik Kenyir could be a premier and yet a sustainable recreational fishing waters in Malaysia.
The objectives of this study are:
1. To determine the number of species of fish in Pengkalan Gawi – Pulau Dula section of Tasik Kenyir and the diversity of these species within the fish population of the lake.
2. To determine the feeding habits of fish species in the fish population of Pengkalan Gawi- Pulau Dula section of Tasik Kenyir.
Freshwater lakes and reservoirs are basins filled with freshwaters (Jorgensen, 2009), that is often and always used by human (Jorgensen et al., 2005). In most research, reservoirs are considered as lakes. Since a reservoir is in appearance like a lake, a reservoir is also known as a man-made lake (Taub, 1984). This was supported by Jorgensen et al. (2005) that described both natural lakes and reservoirs are considered as lakes. This is due to that many features of natural lake and reservoirs are similar (Jorgensen et al., 2005).
Reservoir was created due to the dams construction. According to Cech (2009), dams are basic and fundamental management tools used to control, regulate and deliver water for variety of purpose. A river and natural lake were transformed into a reservoir by regulating its flow. Cech (2009) described that dams were used to regulate rivers and it comes with a price which altered natural and human environments. Without a doubt, spectacular and complex changes, from both physical and biological standpoints, are brought about by the creation of a reservoir on a river (Legault et al., 2004).
2.2 Species Diversity of Fish
Traditional definition of ‘species’ according to McFadden and Keeton (1995) is “a genetically distinctive group of populations whose members are able to interbreed freely under natural conditions and are reproductively isolated from all members of other such groups”. According to Dodds (2002), biologists believed that ‘species’ as the fundamental unit of taxonomic division and the scientific system for naming organisms is based on distinguishing species. Biodiversity meanwhile, at the simplest level, is concerned with the variety of species and their evolutionary relationship (Ray and McCormick-Ray, 2004). Hierarchical taxonomic grouping suggest evolution from common ancestors and the taxon of phylum is most basic (Ray and McCormick-Ray, 2004). This has been noted in relation to taxonomic features, size, shape, environmental preferences, interactions with other biota, and strategies for survival (Sigee, 2005).
Whittaker (1972) and Dyke (2008) described species diversity into three categories: alpha, beta and gamma diversities. According to Dodds (2002), within-habitat diversity (alpha diversity) and between-habitat diversity (beta diversity) are additional aspects of biodiversity. Alpha, beta and gamma diversities were described by previous researchers in different ways. Alpha diversity according to Vane-Wright et al. (1991) is the species richness of standard sample sites within individual habitat, while according to Dyke (2008) alpha diversity is the diversity of species within an ecological community. Alpha diversity in such community is normally described as a measure of two attributes; species richness and species evenness (Dyke, 2008).
For beta diversity, Strange (1999) described that it is a dimensionless number representing species turnover, between habitat patches, within region. Beta diversity measures the diversity of species among communities (Dyke, 2008). Beta diversity sometimes called “beta richness” measures the rate of change in species composition in communities across landscape (Dyke, 2008). Thus, beta diversity is inversely proportional to the average probability of any species migration between any two habitat patches (Strange, 1999), and provides a first approximation of area diversity or regional diversity (Dyke, 2008).
Meanwhile, for gamma diversity, it is represents the species richness at a regional scale. According to Dyke (2008) gamma diversity refers to the diversity of species across larger landscape. Vane-Wright et al. (1991) described that gamma diversity is the product of the alpha diversity of a landscape communities and degree of beta differentiation among them. Thus, gamma diversity is used to denote the diversity of different kinds of communities within landscape (Dyke, 2008). These three types of diversities can change independently of one another but in real ecosystems, they are often correlated (Dyke, 2008).
According to Ngoile and Sarunday (2004), over 8,000 species of fish live in the freshwater ecosystem in the world. Lake Nyasa has the highest species diversity in the world, while Lake Tanganyika has a greater diversity of families and it is the richer lake in terms of genetic diversity (Gupta et al., 2004). In Asia, Lundberg et al. (2000) noted that this continent has the most diverse fish family in the world with 121 families and was higher than Latin American (55 families) and African (50 families) inland fisheries. Kottelat and Whitten (1996) reported that East, South and Southeast Asian have a cumulative total freshwater fish fauna of 7447 species.
The freshwater fish fauna of Southeast Asia is diverse, but up to date references on these fish communities are scarce (Lestari, 2004). This is because the biodiversity of aquatic ecosystems is neglected in developed and developing countries (Ngoile and Sarunday, 2004). Zakaria-Ismail (1994) described that the fish distribution in Southeast Asia can be categorized into 5 zoogeographic regions that are: the Malay Peninsula; the Philippines; the Indo-Malayan Archipelago; the Salween Basin and the Indo-Chinese Peninsula. In Malaysia, latest research done by Chong et al. (2010), listed a total of 521 species of freshwater fish inhabiting in Malaysia freshwater ecosystems.
2.3 The Important of Species Diversity
Ray and McCormick-Ray (2004) listed different important of biodiversity to different levels of community including; ecologist and biologist. For ecologist, ways that species function help explain ecosystem pattern and process, while biologist interested on community persistence, resistance, resilience and vulnerability to disturbance (Ray and McCormick-Ray, 2004).
Species evolved to choose the habitats it does best in, thus separating the species by habitat. According to Wilson (1992), opportunistic species evolved very fast to fill the spaces. Sigee (2005) described that the assessment of biodiversity in aquatic habitats is important for a number of reasons including comparison of different natural habitats and in understanding fundamental aspects of community structure dynamics. Lindenmayer and Fischer (2006) listed that habitat diversity is one of the important mechanisms for researchers to observed species-area relationships. When sample sizes were standardized by an area, habitat diversity was the best explanatory variable for species richness (Lindenmayer and Fischer, 2006).
Fish species are also an important indicator of ecological health. The abundance and health of fish will show the health of water bodies (Hamzah, 2007). This was supported by Zainudin (2005) who claimed that fish species diversity has been used as biological indicator to show the level of aquatic pollution towards the environment quality. In most research the total abundance of fish may correlate to the water quality where some of the species decreased whereas others increased (Fabricius et al., 2005).
This is due to the fact that the characteristics of fish make them the most chosen biological indicator. Fishes are very sensitive to most habitat disturbance, and they may display physiological, morphological or behavioural responses to stresses (Hamzah, 2007). Most fishes avoid stressful environments and fish is a good indicator for long term effects in one study area (Hamzah, 2007). In accordance to this, Wilson (1992) concluded that study on biological diversity is the key factor to the maintenance of the world for future generations.
2.4 Factor Influencing Distribution of Fish Species
Kottelat and Whitten (1996) considered biological changes, water pollution, increased sedimentation, flow alteration and introduced species as the main causes in decreased diversity of ichthyofauna. Diet too may be an important factor in determining organism diversity (Cox and Moore, 2010). There are numerous other factors that influencing the diversity of aquatic species in the aquatic ecosystem. According to Dodds (2002), these factors, including habitat type, species interactions, introduction of new species, productivity, species colonization and type of species occur in a specific environment.
2.4.1 Habitat Types and Conditions
Dodds (2002) described that habitat type and species diversity is interrelated. Fish species must specialize in type of habitat they live so that they are able to successfully colonize that area. Although the freshwater environment might appear to be relatively uniform, particularly within the epilimnion, there are some important variations that differentiate habitats (Sigee, 2005). Lake has several types of habitats that are dominated by different groups of organisms and changes in this habitat can influence biodiversity (Dodds, 2002). Kutty et al. (2009) illustrated that the surrounding factors that are not suitable for fish habitat could resulted in low abundance of fish species. Additionally a distribution pattern in which one or a few species are far more abundant than all others may indicate that the habitat lacks a sufficient diversity of structure, patchiness, or resources to allow many species to exist together (Dyke, 2008).
2.4.2 Water Quality
The relationship between water quality and fish diversity is an important factor affecting fish communities (Da Silva et al., 2006). According to Peralta (2004), more diversity of fish can be seen in a water bodies with a greater variety of physical and chemical conditions. Fishes are affected the most by the media in which they live (Khan, 2004). According to study conducted by Barrela and Petrere (2003) water bodies in urban areas showed complete absence of fish species due to the low water qualities parameters. The chemical and physical changes in water may induce alteration in the composition and population of aquatic species and resulted in destruction of spawning grounds (Khan, 2004).
Another factor affecting fish distributions in a lake is the trophic status of the lake. According to Asabina (2001) when the anthropogenic load increases, the ecological capacity of the habitat diminish and environmental problems like eutrophication arise. Heavy accumulation of nutrient also could causes lake eutrophication (Khan, 2004). According to Khan (2004), some of the native fish find them difficult to cope up with the eutrophication and they suffer heavy losses. The development of red-bloom with inherent potential of inducing toxicity in aquatic environments endangering fish is a sign of accelerated eutrophication (Khan, 2000).
2.4.4 Introduction of Exotic Species
The other important aspect in relation to factors affecting fish biodiversity is the introduction of exotics species (Nguyen and De Silva, 2006). Khan (2004) also noted on introduction of species, especially the exotic species for commercial purpose, has resulted in the loss of diversity. The intentional or unintentional introduction of exotic species can cause very serious problems in a given lake (Jorgensen, 2009).
Li (2001) reported that there was a big change in number of families and numbers of species from new families in reservoir in China. Nguyen and De Silva (2006) described that the worst effects on fish biodiversity are extinction of native flora and fauna and disappearance of endemic species. The introduction of exotic species can provoke very dramatic changes in the ecosystem structure not only at the biological community level, but also in a lake’s chemical-physical environment (Jorgensen, 2009). Jorgensen (2009) also listed that the negative consequences of exotic species include the disappearance of native species, reduction in species diversity, reduction of water transparency and changes in algae bloom patterns in a lake. Besides that, introduction of species could bring to the introduction of parasite or diseases that come along with the alien species (Nguyen and De Silva, 2006).
Khan (2004) listed the lost of fish diversity are due to fact that local fish have to compete their food with the exotic species, higher fecundity of exotic species, and better fertilization and growth rate for the exotic species. In some cases, Yousuf (2000) reported that the introduced species have also found to feed on the fry and juvenile of the local fish. All of the factors listed above have caused adverse impact on the fish species diversity in aquatic ecosystems.
2.4.5 Human Activities
Nguyen and De Silva (2006) described that finfish biodiversity was affected directly or indirectly by human activities. Reservoir construction is one example of human activities that resulted in changes in species diversity of fish. Reservoirs have influenced on the diversity of the riverine fish fauna in one area (Li, 2001). Nguyen and De Silva (2006) added that the loss of biodiversity in reservoir and river, and threatened on the indigenous species are resulted from the impoundment. The original riverine environment is transformed to lacustrine environment impeding upstream spawning migrations of fish species and this effects the diversity of the species (Shreshtha, 1997).
Other human activities such as deforestation, agricultural activities and increase of urban areas affect the water quality and the survival conditions of aquatic habitat (Da Silva et al., 2006). Because of deforestation and other detrimental human activities in the catchment areas, most of the breeding grounds have undergone siltation (Khan, 2004). Reclamation of water bodies and their catchment has destroyed the natural habitat of fishes and this has further aggravated the habitat conditions, the consequence of which results in the decrease of fish population (Khan, 2004).
2.5 Measuring Species Diversity
Dyke (2008) described that biologists must measure and express features of biodiversity in ways that are meaningful to others. In addition to that, the final result is easy to present, interpret and compare with others and the number of species present offers a useful approximation of the biodiversity of the area (Dyke, 2008). There are many diversity indices have been used by previous researchers in aquatic ecosystems (Gordon et al., 2004).
Species richness is one of the most intuitive and frequently used measures of biodiversity (Lindenmayer et al., 2005). Lindenmayer et al. (2005) added that species diversity also sometime is called as species richness. This is due to the fact that species richness is the number of species in the community (Dyke, 2008) and species diversity is related to the species richness (Gordon et al., 2004). Gibson (2005) used ‘species numbers’ to compare species, as they represent the most straightforward measure for comparing diversity between and among families. Dyke (2008) preparing ‘species list’ that consisting the total number and names of species to determine a site-specific biodiversity.
According to Gordon et al. (2004), the most widely indices used in measuring species diversity are the Shannon Weaver index, Simpson index and Margalef index. Dodds (2002) considered only three diversity indices in his book; species richness, Shannon-Weaver diversity and evenness, although ecologists have used several other indices of diversity throughout the years. According to Boyle et al. (1990) each of these indices has its strengths and weaknesses.
2.6 Fish Feeding Habits
There are several types of feeding habits of fish and it is different from one to another. Feeding habits according to Jobling (2010) referred to carnivore, omnivore or herbivore feeding habits. According to Moyle and Cech (2004), fish can be classified broadly on the basis of their feeding habits as herbivores, carnivores, omnivores and detritivores.
A number of freshwater fishes are from non-meat eater type which eating on plant materials and this known as herbivore fishes. Herbivory is much more common in tropical freshwaters (Bone and Moore, 2008). Herbivorous fish is known also as phytophagous fishes as described by Bone and Moore (2008). Bone and Moore (2008) added that some herbivore fishes eat on grasses and decaying vegetation, while some of them eat on fruit, flowers and seed that fall into the water. As the plant material in their food is 75.0% or more of the total gut contents, they are considered herbivorous (Khanna, 1993).
Although, plants have no escape mechanism, herbivorous fishes still required to have specific physical characteristic to consumed plants. This fishes generally have small, often interior, mouth equipped with rasping or nipping teeth (Bone and Moore, 2008). Herbivorous fish have the physical equipment to process plants, such as jaw teeth, pharyngeal teeth, and a muscular stomach with grinding material (Gerking, 1994). They have typically a small gape for taking rapid small bites and row of small closely spaced mandibular teeth which function to crop plant materials or scrape it from the substratum (Hart and Reynolds, 2002). The stomach in many herbivorous fishes may be absent (Hart and Reynolds, 2002), but if present, the stomach has a thin walled and it is elastic (Bone and Moore, 2008). Herbivorous fish have longer guts with greater surface area for absorption (Bone and Moore, 2008).
Most fishes are carnivorous which they eat live animal prey during some stages of their lives. According to Sharma (2009), carnivorous fish in freshwater aquatic ecosystems are secondary consumers; which fed on the herbivores species, and they are also tertiary consumers; which is the top consumers. Basically, most of the fishes under this classification are active predators. According to Bone and Moore (2008), the vast majority of living fishes are predatory and predatory is also known as piscivorous. Piscivores are usually thought to be few in number in certain habitats, because they are feeding on fish and occupy the top of the tropic hierarchy (Gerking, 1994).
It is common to observe the large fish feeding on smaller fish, and thus occupying the tertiary consumers (Sharma, 2009). Many piscivores eat their prey as whole but others tear and bite the prey into smaller pieces before swallowing it (Jobling, 1995). Carnivorous fishes are strong swimmers, or sit-and wait ambushers, or they may possess camouflage or lures (Bone and Moore, 2008). Sight and visual of the prey are among the mechanisms of predation among fish to detect a prey, which is evident and common in carnivorous fish (Wotton, 1992).
Food of these fishes consists of a very high percentage of animal and crustaceans, insects, larvae, molluscs, smaller fishes and tadpoles (Khanna, 1993). Some of the carnivorous species adapted to feeding on hard shelly prey, with heavy and molariform jaw or pharyngeal teeth (Bone and Moore, 2008). These species have large, terminal or subterminal mouths with well developed grasping and biting teeth (Bone and Moore, 2008). Additional to that Bone and Moore (2008) described that the carnivorous fishes have well defined stomach and the intestine is relatively short.
According to Allsopp et al. (2009), omnivorous fish eat both animals and plants materials. The food of these fishes consists of a varying percentage of plant and animal material, and they form a sort of link between the herbivorous and carnivorous fishes (Khanna, 1993). Teixeira-de Mello et al. (2009), classified omnivorous fish species as; omnivore-benthivorous, benthi-planktivorous, omnivore-benthi-herbivorous, omnivore-benthi-planktivorous and omnivore-benthi-piscivorous.
Seeds, fruits, arthropods and terrestrial vertebrates were the most important dietary categories for omnivorous species (Albrecht et al., 2009). Some of these fish classification eat in a larger amount of plant material, some of them were found eat greater amount of animal while some of them eat nearly equal between plants and animals. The proportions of dietary items varied in relation to fish size and water dynamics (lotic or lentic syatems) (Albrecht et al., 2009). Additional to that Albrecht et al. (2009) described that omnivorous species in aquatic ecosystems can overlapped broadly in their diets. Bone and Moore (2008) described that the ratio of gut length to body length is between 1 to 3 in omnivorous fishes.
Another major feeding guild in fishes consists of plankton filterers (Bone and Moore, 2008). A successful plankton filterer needs to be able to separate plankton from the water through mechanical filtration by means of gill rackers (Bone and Moore, 2008). According to Gerking (1994) filter-feeding is to strained plankton from the water by the gill raker apparatus, where the fish open its mouth while swimming forward. Planktivorous species basically were divided into two categories that are zooplanktivorous and phytoplanktivorous. Hajisamae et al. (2003) classified phytoplanktivorous species due to the species consuming almost entirely phytoplankton. Meanwhile according to Moncayo-Estrada et al. (2010) fishes selecting prey from the zooplankton communities are known as zooplanktivorous fish species.
Phytoplanktivorous fish are important due to the role in aquatic ecosystems as direct consumers of phytoplankton primary production and in biological management of algal blooms (Xie and Liu, 2001). Phytoplanktivorous fish species have specific anatomical and physiological adaptations for feeding on toxic phytoplankton because these fishes more resistant to cyanotoxins exposure (Xie et al., 2003). Some of this species have developed gizzard-like stomachs that serve to break down the cell wall of blue-green algae, diatoms, filamentous, red and green microalgae that ingested along with sediment materials (Hart and Reynolds, 2002). Bone and Moore (2008) described that some filter-feeders, especially those phytoplanktivorous have exceedingly long guts.
Meanwhile, for the zooplanktivorous species, Ross et al. (2006) described that some juvenile and adult fish of this, have a filtration system with fine unicuspid jaw teeth and ornamented branchial arches. Zooplanktons were picked individually by sucking or biting movements. According to Gerking (1994) there are two general mechanisms for capturing zooplankton which are filter-feeding and particulate feeding. All predators that feed in this manner search and discover their prey by visual means which distinguishes the particulate feeders from the filter feeders (Gerking, 1994). Recent study done by Davidson et al. (2010), found that zooplanktivorous fish density significantly influenced the community composition of zooplankton in aquatic ecosystems.
Detritus always contains silt, sand or other non organic particles such as bacteria, algae, and other unicellular organism. These materials and its associated bacteria are consumed by detritivores species and this species derive their nutrients from it (Speight and Henderson, 2010). Some species do ingest large quantities of detritus and their preference for this food source should be recognized (Gerking, 1994). According to Bone and Moore (2008) detritivores species feed also on phytoplankton and mud particles. Earlier study done by Keenleyside (1979), reported that fish whose stomachs contain detritus are assumed to be feeding directly on it.
According to Bone and Moore (2008), detritivores may have either a one-part stomach; which has a long intestine, or a two-part stomach; which with a short intestines. In terms of feeding strategies, Gerking (1994) listed 4 types of feeding strategies for detritivorous which are biters, suction feeders, scoopers and filterers. Many detritivores are bottom suckers that typically posses small, undershot inferior mouths (Bone and Moore, 2008). Detritivores fishes swim along near the bottom sucking the surface material and spitting out larger particles where the rest will be swallowed (Gerking, 1994).
2.7 Factors Affecting Fish Feeding Habits
Feeding habits of fish in aquatic ecosystems depend on several factors. According to Houlihan et al. (2001), there are two major factors that affecting the fish feeding habits of fish which are the abiotic and biotic factors. These according to Jobling (2010), may be categorized broadly as; the characteristics of the fish, food characteristics, factor related to the environment and factor related to food availability. Food characteristics are appearance of the food in terms of size, shape and colour meanwhile, fish characteristics are life stages, health status, and behavioural features (Jobling, 2010).
2.7.1 Abiotic Factors
Abiotic factors that affecting feeding habits in fish are light, temperature, other physical factors and chemical factors (Houlihan et al., 2001). Colour is also known to affect capture rates of live prey that affecting feeding habits (Chesney, 2005). According to Bernier (2006), temperature, hypoxia and ammonia are known to affect fish food intake. Jobling (2010) categorized light, temperature, water flow, currents and water quality parameters as environmental conditions that affect fish feeding habits. There is unique relationship between environmental parameter and ingestion rate in fish (Bernier, 2006). According to Chesney (2005) these environment factors, such as the quality and quantity of light, temperature and turbidity have effects on capture rates of prey in fish.
Turbidity was highlighted by Ang and Petrell (1997), where this parameter interferes with light penetration and the ability of fish to detect food, so is generally deemed to have a negative effect on feeding. The other abiotic factor that was highlighted by previous researchers is water temperature. Changes of water temperatures can show the changes in the feeding activity of fish. Fish will loose appetite in the lower temperature range, but feed intake can be underestimated (Houlihan et al., 2001). Other physical factors also influencing fish feeding habits. These physical factors listed by Houlihan et al. (2001) are waves and water currents, where wave height and its frequencies have an impact on feeding of fish. Meanwhile, the chemical factors that were listed by Houlihan et al. (2001) are dissolved oxygen, pH, nitrogenous compounds and salinity.
2.7.2 Biotic Factors
There are some biotic factors that affecting on fish feeding habits. These factors according to Houlihan et al. (2001) are the social structure of the fish, predators and human disturbance. Meanwhile, according to Helfman (2007) biotic interactions in fish are in the form of predation, competition or hybridization. Parasites too can affect food intake in fish via variety of different mechanisms (Bernier, 2006). Bernier (2006) described that parasites could affect feeding habits of fish through affecting their appetite, reducing stomach capacity, damaging the alimentary canal or affecting the foraging behaviour.
According to Houlihan et al. (2001) social environment of fish may be influenced not only by population density, but also by factors such as size heterogeneity and sex ratio of the fish. According to Chesney (2005), prey size is one of the most significant factors affecting prey capture success in fish and it is strongly related to the mouth size of the fish. ‘Food preferences’ is also a biotic component that influences on fish feeding habits. Food preferences affects the rate of encounter between predator and prey and this may result in a predator showing a positive or a negative preference for a prey type (Hart and Reynolds, 2002).
2.8 Methods of Determining Feeding Habits
In recent years, feeding habits of fish can be documented by watching one species eating another, or through ‘stomach contents analysis’ (Helfman, 2007). According to Kapoor and Khanna (2004), many ecologists have attempted to estimate food consumption by fish, using direct methods on ‘stomach contents analysis’. Previously, several methods were used by researchers to provide a quantitative description of these samples (Hynes, 1950; Windell, 1971; Hyslop, 1980), but according to Wootton (1998) no one method is entirely satisfactory. However, many latest researches that studies on stomach contents analysis (Hajisamae et al., 2003; Peralta, 2004; Kariman and Khalifa, 2009) were followed to the methods described by Hyslop (1980). These are ‘occurrence methods’ and ‘numerical methods’.
2.8.1 Occurrence Method
Percentage ‘frequency of occurrence’ is the simplest method to represent fish diet in the fish stomach (Wootton, 1998; Tollit et al., 2010). Stomach contents were examined and the ‘individual food organisms’ were sorted and identified (Windell, 1971). This method is referred to the ‘percentage of fishes’ in a sample that contains a determined feeding category (Eduardo et al., 2006). In the ‘frequency of occurrence’ method, the occurrence of the food items was expressed as the percentage of the total number of stomach containing food (Kariman and Khalifa, 2009).
This is similar to Hajisamae et al. (2003), where they described that the percent ‘frequency of occurrence’ is the number of stomachs in which a particular food item was present, and express as a percentage of the total number of non-empty stomachs. This method just considered on ‘type of food item’ consumed by the fish but it was not included with the ‘quantities of food item’ in the stomach. In general, occurrence indices may over estimates the importance of small prey (Tollit et al., 2010).
2.8.2 Numerical Method
In the ‘numerical method’, the number of items in each food category is counted in all stomachs in the samples (Wootton, 1998). ‘Numerical frequencies’ of prey items in the samples were calculated and were converted to percentage (Seefelt and Gillingham, 2006). Kariman and Khalifa (2009) clarified that in this method, the number of ‘each food item’ was expressed as the percentage of the ‘total number of food items’ found in the stomach.
Numerical ‘count of prey’ is a simple method to overestimating the importance of small prey due to the differences in the number of prey consumed per meal (Tollit et al., 2010). According to Hart and Reynolds (2002), this calculation provides an estimate of the relative abundance of a particular food item in the diet. This method emphasizes the importance of small and numerous items such as plankton in the fish stomach (Wootton, 1998).
2.9 Water Quality Parameters
‘Water quality parameters’ are the chemical and physical characterization of water and it depends on the local geology and ecosystem (Manivanan, 2008). The water quality of surface water, affects almost in all aspects of life (Palmer, 2001). According to Sturman et al. (2004), the quality of water is ditermined by the presence of substance in the water. The monitoring requires either field measurement in situ or the collection of water samples that are analyzed in the laboratory (Palmer, 2001). Some of the important water quality parameters in water bodies listed by Manivanan (2008) and Staddon (2010) are; temperature, dissolved oxygen, pH, ammonia-nitrogen, nitrate-nitrogen and phosphorus-orthophosphate. According to Sturman et al. (2004), the determination of a few simple substances or a combination of substance will sufficient to measure the quality of water in one water body.
Temperature according to Manivanan (2008) is a physical property that underlines the common notions of hot and cold. The Celsius (⁰C) scale is used for temperature measuring purposes and something that is hotter generally has greater temperature (Manivanan, 2008). With increasing temperature, most gases in the water decreased their solubility. This is due to many of the coefficients, rate parameters, dissolved oxygen, saturation concentration and unionized portion of ammonia are temperature dependent (Palmer, 2001). According to Munro and Roberts (2004), water temperature also affects the aquatic environment that is important for fish health. Fish have their optimum, upper and lower temperatures tolerance limits. These optima vary with species and may be different for different parameters such as oxygen tension and water pH (Munro and Roberts, 2004).
2.9.2 Dissolved Oxygen (DO)
Dissolved oxygen is the oxygen that freely available in water, vital to fish and other aquatic organisms (Manivanan, 2008). According to Staddon (2010) the DO test should be done on site. It is usually used as a water quality indicator in most water bodies (Manivanan, 2008). Dissolved oxygen is one of the best indicators of water body stability where the higher DO the better water quality (Staddon, 2010). It is required for most aquatic life and originated from external supply, photosynthesis, surface re-aeration and denitrification (Palmer, 2001).
In fish, the amount of oxygen consumed is dependent on temperature, where the higher the temperature, the more rapid they uptake the oxygen (Sturman et al., 2004). This is because fishes are cold blooded and their metabolism rises as temperature goes up (Staddon, 2010). Dissolved oxygen levels, although temperature-dependent, are often by themselves an important factor affecting the growth rates of fishes (Moyle and Cech, 2004). Typically, fish prefer DO concentrations between 5 to 8 mg/l, minimum concentration from 3 to 4 mg/l and desired concentration from 5 to 7 mg/l (Palmer, 2001). If the DO drops below 5 ppm this often results in ‘fish kills’ (Staddon, 2010).
The scale which is used to describe the concentration of acid or base in water is known as pH (Staddon, 2010). pH is classified by Manivanan (2008) as chemical water quality parameters. In dilute aqueous solutions, the pH is defined as the negative logarithm of the hydrogen ion concentration (Munro and Roberts, 2004). According to Brooks et al. (2003) the pH of water can be defined as the negative log base 10, of the hydrogen ion (H+) activity in moles per litre. Staddon (2010) described that a pH 7 is neutral, pH above 7 are alkaline and below 7 are acidic, and the scale runs from 0 which is very acidic to 14 which is highly alkaline. The best level of pH water for most fish species are 6 mg/l to 9 mg/l.
The turbidity is a decisive factor in the transparency of water (Manivanan, 2008). The turbidity measurement, which is a light transmittance measurement, is frequently used in natural water bodies (Palmer, 2001). Usually, the lakes and the most of the smaller streams of the tropics are quite clear, but the large rivers are turbid with high suspended or dissolved materials (Moyle and Cech, 2004). Turbidity may effects fish feeding habits. Turbidity interferes with light penetration and the ability of fish to detect food, so is generally deemed to have a negative effect on feeding (Ang and Petrell, 1997). However for some species, the reduced of light intensity because of increase turbidity has been promote feeding under some circumstances.
Light depth, water transparency (Manivanan, 2008), and water turbidity can be measured using a Secchi disk. Secchi disk is a disk that is painted in alternating white and black quadrants (Palmer, 2001). The depth at which the disk is no longer visible is the Secchi depth, and is a measure for transparency (Manivanan, 2008).
Manivanan (2008) listed ammonia, nitrate and phosphate as nutrients in water bodies. According to Palmer (2001), nutrients in water quality studies considered only on the vegetation nutrients, and one of these is nitrogen. Nitrogen primarily found in the soil as nitrate-nitrogen, is soluble and is transported in surface runoff or in subsurface drains (Hebblethwaite and Somody, 2008). According to Staddon (2010), nitrogen compounds such as nitrate are essential for healthy plant growth. Nitrate is a nutrient for algal growth but it can gives health hazard at very high concentrations in drinking water (Manivanan, 2008). The presence of excessive amounts of nitrates in water supplies presents a major pollution problem where nitrates in conjunction with phosphates can cause algal blooms (Staddon, 2010).
In freshwater ecosystem, ammonium concentrations are usually low when compared to the other nutrients. Ammonia is inorganic form of nitrogen; product of hydrolysis of organic nitrogen and identification (Manivanan, 2008). Nitrogen such as ammonia can be in dissolved and solid forms, and both in organic and inorganic forms (Palmer, 2001). According to Palmer (2001), nitrogen is toxic to fish in its ammonia form but ammonia is preferred nutrient for micro-organisms. Ammonia is also preferentially used by phytoplankton over nitrate (Manivanan, 2008). As such the presence of ammonia-nitrogen reduces dissolved oxygen concentrations and adds nitrate to the water (Manivanan, 2008).
Phosphorus is an aquatic plant nutrient and this nutrient limits excessive aquatic plants growths (Palmer, 2001). Sturman et al., (2004) described that the water containing this element is important for algal growth. Meanwhile, according to Manivanan (2008), phosphate is the actual nutrient in the water body that promote the growth of algae. In fact, phosphorus occurs as organic and inorganic phosphate and in nature, usually exists as part of a phosphate molecule (USEPA, 1997). Inorgaic phosphorus in the forms of phosphate plays a major role in biological molecules where living cells utilize phosphate to transport cellular energy (Manivanan, 2008).
Primary source of phosphates are agricultural run-off and detergent residue in urban wastewaters (Staddon, 2010). According to Palmer (2001), these domestic wastewaters are a source of phosphorus and can caused excessive aquatic plant growths, which will result in a degraded water quality. That is why phosphorus controls the trophic status of one lakes (Dillon et al., 2004), where the process leading to enrichment of a water body with nutrients is called eutrophication (Sturman et al., 2004).