An Investigation of Fish Species Diversity, Abundance ...

Journal of Animal Science Advances

An Investigation of Fish Species Diversity, Abundance and Diets of Selected Predator Fish in Insukamini Dam, Zimbabwe Dube A. and Kamusoko R.

J Anim Sci Adv 2013, 3(3): 121-128 DOI: 10.5455/jasa.20130331052157

Online version is available on: www.grjournals.com

ISSN: 2251-7219

DUBE AND KAMUSOKO

Original Article

An Investigation of Fish Species Diversity, Abundance and Diets of Selected Predator Fish in Insukamini Dam, Zimbabwe 1

Dube A. and 2Kamusoko R.

1

Ministry of Science and Technology, Harare, Zimbabwe. Directorate of Quality Assurance and Graduate Studies, Chinhoyi University of Technology, Chinhoyi, Zimbabwe.

2

Abstract A total of 8 fish species (n=465) were caught by gill nets from December 2009 to May 2010 to investigate fish ecology in Insukamini dam. The species were identified as: Serranochromis robustus (n=18), Micropterus salmoides (n=36), Clarias gariepinus (n=72), Oreochromis mortimeri (n=192), Oreochromis macrochir (n=27), Tilapia rendalli (57), Tilapia sparrmanii (n=6) and Oreochromis niloticus (n=57). The largest catches of fish were recorded in February (n=210). O. mortimeri reported the most abundant fish species of 41.29 %. The least abundant fish species of 1.29 % was found in T. sparrmanni. C. gariepinus had the highest mean standard length and weight of 40 cm (ranged from 31.5 to 51.0 cm) and 1082.8 g (ranged from 506 to 1 220 g) respectively. T. Rendalli showed the lowest mean standard length and weight of 16.4 cm (ranged from 12.4 to 25.0 cm) and 215.8 g (ranged from 180 to 350 g) respectively. The diets of S. robustus, M. salmoides and C. gariepinus comprised of fish, snails, insects and worms. Fish were the most dominant food for the predators accounting for 94 % of the stomach contains in M. salmoides. The stomach of C. gariepinus contained 78.8 % unidentified digested material while S. robustus had 11.8 % empty stomachs. The total numbers and sizes of fish caught were mainly affected by predation, poaching, inter- and intra-specific competition and gill nets of the same inch size that were used.

Key words: Insukamini dam, fish species diversity, diet, predator, size, abundance



Corresponding author: Ministry of Received on: 08 Jan 2013 Accepted on: 21 Mar 2013 Online Published on: 31 Mar 2013

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Science and Technology, Harare, Zimbabwe.

J. Anim. Sci. Adv., 2013, 3(3):121-128

AN INVESTIGATION OF FISH SPECIES DIVERSITY, ABUNDANCE AND …

Introduction Zimbabwe is a landlocked and semi-arid country located in Southern sub- Saharan Africa. The country is characterised by large variations in annual rainfall with very few perennial rivers and lacks natural lakes. As a result all stored water is held in constructed reservoirs such as dams and ponds. The history of dam construction dates back to 1902 in Zimbabwe. The government and nongovernmental organisations (NGOS) are embarking in dam construction projects particularly in drought prone communal areas of Zimbabwe. The dams range in size from small reservoirs to large dams used to supply water for urban mining and industrial areas and large-scale irrigation (Rusere, 2005). The major reasons for building dams are to supplement water for irrigation purposes and for supplying water to the community. Most of the dams have now emerged as a source of revenue by supporting commercial and/ or subsistence fishing activities. For example in Zimbabwe, five reservoirs namely Kariba, Chivero, Manyame, Mutirikwi and Mazvikadei are the most important commercial fish stocks exploited by fishers. Amongst these, Lake Kariba provides almost 90 % of the country’s fish production. Besides, fish production Lake Kariba has created employment to approximately 3000 people and enhance capacity building through engaging students from learning institutions in research activities. Fish for subsistence purposes are mainly provided by small dams, rivers and ponds in Zimbabwe. In Zimbabwe, constructed dams are governed under the jurisdiction of Zimbabwe national water authority (ZINWA) and National Parks and Wildlife Authority of Zimbabwe (NPAZ). Fisheries, and in general inland fisheries, have long been one of the sources of food as well as a means of livelihood in tropical regions of the world (Neiland and Bene, 2008). Fisheries development in tropical waters has been greatly intensified in recent years due to rapidly rising human populations. Such development has stimulated studies on fish ecology: the species present, fish population dynamics, growth and the reproduction rates, trophic (feeding) interrelationships and causes of mortality (LoweMcConnel, 1975). The responsible authority, 122

NPAZ, rarely carries out detailed systematic studies in most of the dams in rural areas. They rely on the data provided to them by fishing communities operating in the areas while most of the fishermen are not well versed in fish identification and ecology (Lowe-McConnel, 1975). Therefore, there is lack of empirical scientific data regarding fish ecology and production in such areas. There is need to educate fishermen on how to properly identify the fish species in their areas if proper fish conservation strategies are to be envisaged. Insukamini dam is located in Vungu district of Midlands province. It was built in 1987 to provide water for household use and irrigation. The dam has a volume of 7, 85 x 106 m3 full capacity and is fed by Ngamo River and its tributaries (Moyo et al., 2009). Data on fish studies in Zimbabwe are often limited to large dams and/ or lakes such as Lake Chivero and Lake Kariba. The status of the knowledge on fish ecology of Insukamini dam is weak and patchy despite the widespread recognition of fish as means of livelihood to the communities. The impact of exotic fish species introduced into these small dams on native fish species is not known and well documented. There is need for provision of concrete scientific data to support fish farming activities and fish ecology of Insukamini dam. The major reason is to educate the local community on proper fish identification and how to implement effective conservation strategies particularly on our indigenous fish species. Therefore, the present study was done to investigate the diets of selected fish species, fish species diversity and abundance of fish caught during commercial fishing activities in Insukamini dam. Materials and Methods Study Site Insukamini dam located in Vungu district of Midlands province was built in 1987 to provide water for irrigation. It is located at geographical coordinates latitude 19° 22'31' S and longitude 29° 35'23' E. The dam is 11km long and 120m wide at its widest point. It carries a volume of 7, 85 x 106 m3 in its full capacity, a surface area of 204 hectares, crest length of 888m, a wall height of 18 m and catchment area of 1636 km2 (Moyo et al., J. Anim. Sci. Adv., 2013, 3(3):121-128

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2009). Its catchment area comprises mainly of rural agricultural communal lands and partly peri-urban settlement surrounding Mkoba village, Gweru. The dam is in the lake Zambezi basin and receives water from Ngamo River and its tributaries. Fish collection Sampling was carried out monthly for a period of 4 months. The dam was sampled once every month for a period stretching from mid December 2009 to the end of May 2010. In January and April, there were no fish specimens collected. Fish were collected using gill nets of 3.5 and 4 inch mesh size. The gill nets were set parallel to the shore and sometimes across the mouth of the bay. Gill nets were set in the late afternoon and retrieved early the next morning (from 1700hrs to 0600hrs). Identification of fish species The caught fish were identified to species level using the keys according to the method of Bellcross and Minshull (1988) and were enumerated. Furthermore, a sample of 60% of caught fish was selected for further characterisation. Standard length and weight of each individual fish were measured. Fish diet The stomachs of selected fish were dissected out and preserved in 5 % formalin for 24 hrs to allow fixation of tissues and then stored in 75 % alcohol. The contents of each stomach were suspended in 100ml of water per gram of stomach and examined under an inverted microscope according to the method of Mhlanga (2003) and Zengeya and Marshall (2007). Each item in the diet was identified to the lowest possible taxonomic level. The fish diet was determined by the frequency of occurrence method, which records the percentage of stomachs containing a particular food item out of the total stomachs containing food (Zengeya and Marshall, 2007). Statistical Analysis Standard statistical computations were done using Graph Pad Prism version 6.01software program. Percentage frequency of occurrence was calculated using the formula: {Number of stomach contains food / number of stomachs examined}. 123

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Results and Discussion Fish species diversity and abundance A total of 465 specimens comprising 8 fish species (both indigenous and exotic) were collected from Insukamini dam during the study. The fish population largely consisted of cichlids, Oreochromis mortimeri Trewavas, 1966, Oreochromis niloticus, Tilapia rendalli (red breast tilapia) Boulenger, 1896, Oreochromis macrochir (green head tilapia) Boulenger, 1912, Serranochromis robustus Boulenger, 1896, Tilapia sparrmani Smith, 1840 and Micropterus salmoides, large mouth bass Lacepede, 1802, Catfish, sharp tooth catfish Burchel, 1822. Figure 2 (A-D) shows the number of fish caught from Insukamini during the sampling period. The highest number of fish was caught in the month of February recording a total of 210 fish. This might have been due to favourably low temperatures and high level of water in the dam that was 100.092% full. During this time more food was available therefore most fish species migrated to the surface of water. The total number of fish caught in December (73 fish) was less than that of February. Wind rainy and high temperatures experienced in December may be a reason for the low number. The least number of fish were caught in March. The number of fish caught in that month was 38. This was due to the hiking of the licence fee by NPAZ to a price far beyond the reach of communal fishermen so they ended up resorting to illegal fishing activities. The absence of fishing licence also affected sampling in the month of January and April since no samples were collected. Another reason that may have affected the numbers of fish collected during the study was one type of gill nets with 3.5 and 4 inch mesh size was used. Net and mesh size characteristics vary depending on the type of fisheries and their target species (Uhlmann, 2003), therefore may have affected the size and type species caught from the dam. The most abundant fish species was O. mortimeri, which represents 41.9% of 465 fish caught during the study. It represented the highest number of fish species caught throughout the sampling period although it has been listed as endangered species in some larger lakes such as Kariba. O. mortimeri is an indigenous fish species


therefore it has the ability to adapt and establish well in any fresh water resources of Zimbabwe. Restocking the dam could be probably another reason for high numbers of O. mortimeri species that is used in fish farming activities in most artificial water bodies across the country. The phenomenal increase is also attributed to suitable breeding conditions created by rising level of the dam as reported in Lake Kariba (Jackson, 1961). O. mortimeri has a relatively short breeding cycle and breeds practically all year (Skelton, 2001), therefore it multiplies fast thus increasing its abundance and chances of being caught (Trewavas, 1983; Bell cross- Minshull, 1988). However, the major threat to O. mortimeri is the exotic species O. niloticus that was introduced in cages by anglers and aquaculturists which is displacing the indigenous species throughout its range (Chifamba, 1998). The two Oreochromis spp. competes directly for food and space. C. gariepinus, the African catfish was the second most abundant fish species in the dam with an abundance of 15.5 %. More numbers of C. gariepinus were caught when the nets were set along the shore of the dam. The fish species favoured turbid environments and the shore areas that were covered with vegetation. Comparing to other fish found in the dam, catfish being an omnivore can utilise a variety food within its vicinity and reduce inter-specific competition from species such as M. salmoides and S. robustus (Skelton, 1993). O. niloticus and T. rendalli were also highly abundant with 12.3 and 12.6 % respectively. O niloticus is an exotic fish species in Zimbabwe. The fish was introduced into dams for boosting fish production in artificial water bodies. In other dams, it has been able to displace other species and become the most abundant fish species. The fish was introduced because of its short generation time as compared to other cichlids (Lowe- McConnell, 1987). According to Chandra et al. (2008), O. niloticus is a larvivorous fish which feeds on immature stages of mosquitoes, a probable reason for its introduction in most dams for biological control of mosquitoes. O. niloticus is an omnivore which preys on and competes with other freshwater fish, destroying their habitats (especially nests) and 124

consuming native aquatic vegetation thereby altering the shallow-water ecosystem in their new habitats (GISP, 2007). Another reason for their large number in the dam is niche segregation between the adult fish and its juveniles which intends to reduce intra-specific competition. The young ones feed on plants (herbivorous) while the adult are predators (carnivorous) (Skelton, 1993). The introduction of O. niloticus reduces clutches of indigenous fish species particularly the tilapias (Trewavas, 1983). O. niloticus is a vigorous invader and has the potential to displace some local species in the dam. T. rendalli (red breast tilapia) is an indigenous fish species. Its presence was natural although the species was introduced into Zimbabwe to control weeds and the amount of vegetation in dams since the fish is a vegetarian (LoweMcConnell, 1987; Bell-cross and Minshull, 1988). The abundance of T. rendalli was lower than that of O. mortimeri and C. Gariepinus. This can be attributed to predation by S. robustus, M. salmoides and C. gariepinus. According to Dalu et al. (2012) largemouth bass M. salmoides and S. robustus were introduced into Zimbabwe in 1932 and early 1960s respectively. They have impacted Barbus spp. diversity and abundance in many streams. Figure 1 shows the data for the abundances of fish species caught from Insukamini dam. However, S. robustus, M. salmoides, O. macrochir and T. Sparrmanii species were in relatively low abundance despite the predacious effect of some of these species. The reason for this decline in numbers might be inter-specific competition amongst the fish species since most fish species overlap in terms of dietary requirements. For example, the presence of O. niloticus which is a true omnivore has been implicated in depletion of most indigenous fish species (Trewavas, 1983). T. sparrmanii, an omnivorous fish species also competes with O. mortimeri for food contributing to low number of this species caught during the research. The two macrophages Tilapia sparrmanii and T. rendalli, which are usually macrophages with macrophytes, have a dietary overlap as reported in the study carried out in Lake Chivero by Zengeya and Marshall, (2007). J. Anim. Sci. Adv., 2013, 3(3):121-128

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Fig. 1. The abundances of fish species caught from Insukamini dam.

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Fig. 2. (A-D). Showing number of fish caught in the month of December, February, March and May respectively.


Therefore interspecific competition between these two species may account for the increase in the abundance of T. rendalli and a decrease in the number of Tilapia sparrmanii. Two piscivorous fish species, the indigenous S. robustus and the exotic M. salmoides that were present in the dam have almost similar dietary needs. This could be a possible reason for the decline of S. robustus species in the dam due to inter-specific competition. The interaction of different size classes within (and between) species may have also created very complex competitive interactions in fish communities that led to reduction in fish catches (Bergman and Greenberg, 1994). Poaching by unlicensed fisherman was also a major influence on the reduction of fish species diversity as well as abundance.

Sizes of caught fish The mean standard length and weight varied according to the species of fish that was caught. C. gariepinus had the highest mean standard length and weight of 40.3 cm (ranged from 31.5 to 51.0 cm) and 1 082.8 g (ranged from 506 to 1 220 g) respectively. The lowest mean standard length and weight was recorded in T. rendalli. The mean standard length of T. rendalli was 16.4 cm and ranged from 12.4 to 25.0 cm while the mean weight was 25.8 g and ranged from 180 to 350 g. The data are shown in table 1. The length-weight relationship of all fish species caught during the study was not determined. The fishermen were using gill nets with a mesh size of 4 inches, so most of the specimens were assumed to be almost of the same size.

Table 1: The minimum, maximum and mean values of weight and standard length for fish caught by gillnets from Insukamini dam. Standard length (cm) Weight (g) Species Number Min Max Mean Min Max Mean S. robustus 17 21.5 24.4 23.5 288 350 302.7 M. salmoides 36 18.2 32.0 23.3 300 1100 654.8 C. gariepinus 72 31.5 51.0 40.3 506 1220 1082.8 O. mortimeri 192 14.3 25.5 19.8 240 500 378.0 O. macrochir 27 16.2 28.7 21.2 348 400 371.4 T. rendalli 57 12.4 25.0 16.4 180 350 215.8 T. sparrmanii 6 18.4 22.5 20.3 385 394 389.5 O. niloticus 57 14.6 24.0 20.6 190 400 377.9

Fish diet S. robustus and M. salmoides were feeding primarily on fish. The main food items of M. salmoides were fish since 94 % of the stomachs examined contains fish. M. salmoides also consumed terrestrial and aquatic insects. Unidentifiable digested material was recovered in 22.2 % of the examined stomachs. In a similar study conducted by Lorenzoni et al. (2002), information was gathered on the feeding habits of the largemouth basses, M. salmoides. It was observed that the diet of M. salmoides comprised of the grass shrimp Palaemonetes antennarius (Crustacea, Palaemonidae) although fish were not frequent and insects were scarce. The fish species that were identified in the largemouth basses stomach include the Eastern mosquito fish Gambusia holbrooki Gir., sand smelt Atherina boyeri Risso, pumpkinseed 126

Lepomis gibbosus L., spined loach Cobitis taenia L., perch Perca fluviatilis L. S. robustus was a carnivore since the dissected stomachs contained zooplankton such as fish and terrestrial insects. The most abundant food item of S. robustus was fish since 52 % of the examined stomachs contained small fish. Skelton (1993) reported the prey of S. robustus as fish juvenile though most often eat minnows. Comparatively, Zengeya and Marshall (2007) reported some ontogenic dietary shift from zooplankton to a wide range of food items depending on the standard length in S. robustus species caught from Lake Chivero. However, Winemiller (1990) identified mostly immature catfishes of the genus Synodontis (Mochokidae) followed by a smaller fraction (by volume) of Barbus species (Cyprinidae) as the main diet consumed by S. robustus as a population. The main diet of C. gariepinus also consisted of fish although J. Anim. Sci. Adv., 2013, 3(3):121-128

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78.8 % was found to be unidentified digested material. C gariepinus had a variety of diet that ranged from snails, worms, grass to fish. The African catfish is an omnivore with preference for plankton diet (Ayinla, 1988) therefore the unidentified digested material found in the stomachs could be a mixture of both plant and animal food materials. It was difficult to identify the fish species and even the digested food material in the stomachs because of the advanced stage of digestion. There was a very low incidence of empty stomachs amongst the caught fish species ranging from 0 to 11.8 %. This can be attributed to low temperatures

during the period of sampling stretching from early rainy season (mid December) to early winter season (end of march) which resulted in increased level of dissolved oxygen through out the water column. According to Dalu et al., (2012), high temperatures may reduce feeding in most fish species as they slow down their metabolism with decrease in dissolved oxygen levels causing a significant reduction in food conversion and growth amongst the species. The converse is true for low temperatures thus supporting the findings of the study. The data for the percentage stomach contains in selected fish species and their numbers are shown in table 2.

Table 2: The numbers of fish caught (N), the percentage with empty stomachs and the proportion of stomachs containing different food items in fishes from Insukamini dam. Percentage stomach contains Species N Empty stomach (%) Unid Fish Aqui Teins Coinsect Snails Worms S. robustus 17 11.8 29.4 52 0 9 0 0 0 M. salmoides 36 0 22.2 94 13.9 8.3 0 0 0 C. gariepinus 72 0 78.8 33 29.9 36.6 16.7 33.3 16.7 Coins = combined terrestrial and aquatic insects; Unid = unidentified digested material; Aqui =aquatic insect; Teins= terrestrial insects.

Conclusion The number of most fish species caught from Insukamini dam and their abundance were very low. Selection pressures such as predation, intra- and inter-specific competition and poaching were implicated for the reduction in fish species diversity and abundance. The sizes of the fish species caught were almost similar due the same gill net that was used throughout the research period. S. robustus and M. salmoides were the most dominant species that played a predatory role on other fish species in the dam although some dietary overlap were also reported. There must be strict enforcement of regulations that govern fishing activities in Insukamini dam to curb poaching and reduce fish species loss. Effective conservation strategies should be implemented by educating fisherman in the surrounding community on fish species identification. References Bell-Cross G, Minshull JL (1988). The fishes of Zimbabwe, Trustees of the National Museum and Monuments of 127

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