ABSTRACT
Some aspects of reproduction, food and feeding habits as well as length weight relationship and condition of Clarias gariepinus in selected Lakes were studied. Samples of C.gariepinus were collected monthly during September (2005) through to August (2006) using hook – and – line method and gillnets of various mesh sizes. Sex ratio was not significantly different from 1:1 except in samples taken in April and July, and in length groups between 25 and 54 cm total length (TL) in the total sample. In all these cases, there was a preponderance of females over males. In the total sample, for instance, females were about 1.26 more numerous than males. The 50% sexual maturity length (L50) was estimated at 50 cm TL for females and 56 cm TL for males. Estimated fecundity, which was linearly related with fish and gonad sizes ranged from 398 to 1165 eggs per gram with a mean of 945. Absolute fecundity was estimated to range from 11,000 to 580,571 with a mean of 159,660. Gonadosomatic index and frequency of ripe gonads suggested that C. gariepinus in Babogaya breeds throughout the year with intensive breeding activity during March to July and less intensively in September. Intensive breeding was coincident with the rainy seasons. C. gariepinus was found to ingest a variety of organisms of plant and animal origins, as well as items including detritus and sand grains. However, insects, zooplankton and fish (Oreochromis niloticus) were found to be the most important food of C. gariepinus in Babogaya. Thus, the fish is considered to have a mainly carnivorous feeding habit. The major food items ingested were all size groups of the fish during all sampling months of the study. However, the importance of insects and zooplankton tended to decrease whereas that of fish tended to increase with the TL of C. gariepinus. Thus, it appeared that the fish feeds progressively more O. niloticus as it grows larger. However, based on predator to prey size ratio of which 85 % range between 1:5 to 1:30, there was no direct correlation between the size of C. gariepinus (predator) and that of its prey (O. niloticus). High incidence of empty stomachs was observed during the whole sampling period. But, the frequency of empty stomach was high during the rainy season, which could be associated with breeding activity. The contribution of insects and zooplankton to the diet of C. gariepinus was relatively highest towards the end of the main rainy season, whereas the contribution of O. niloticus was relatively high during the rainy season. The relationship between total length (25 to 102 cm) and total weight (165 to 7000 g) was curvilinear and represented as TW = 0.0156 TL2.934, R2 = 0.942, P < 0.05. Fulton condition factor (mean ± SE) was 0.66 ± 0.04 for females, 0.63± 0.03 for males and 0.64 ± 0.01 combined for both sexes.
CHAPTER ONE
INTRODUCTION
Providing adequate food for a rapidly increasing human population is one of the greatest challenges in the world. The problem is particularly acute in countries like Nigeria where, besides population explosion, natural and man-made calamities have aggravated the problem. In addition to increasing food production from land agriculture, it is, necessary to sustainably exploit the aquatic ecosystems to contribute towards the effort of food security by virtue of their high productivity. Nigeria’s fish resources could undoubtedly offer one of the solutions to the problem of food shortage in the country.
Nigeria is endowed with sizable amount of lotic (running) and lentic (stagnant water) environments whose fishery potential has not yet been fully realized (Brook Lemma, 1987). The inland water body of the county is estimated at about 7,400 km2 of lake area and about 7,000 km total length of rivers (Shibru Tedla, 1973). These water bodies harbour more than a hundred edible fish species, and the annual potential fish yield of the main lakes is roughly between 30,000 and 40,000 metric tons (FAO, 1995). However, current exploitation is about 20 % of the potential, and a few species contribute to the fishery (FAO, 1995). Therefore, though some stocks show signs of overfishing, the fishery could be expanded so that it can contribute to food security and the economy. Such an opportunity is provided by Lake Babogaya; one of the Bishoftu crater Lakes. Lake Babogaya harbours the African catfish, Clarias gariepinus, and two tilapiine species (Oreochromis niloticus and Tilapia zilli), which were introduced in to the Lake by MOA (Ministry of Agriculture) with the aim of fishery development. Needless to say, sustainable exploitation requires scientific knowledge of the resource. gariepinus is a widely distributed species, and contributes greatly to the fishery of Africa (Willoughby and Tweddle, 1978; Viveen et al., 1986) and Nigeria (Shibru Tedla, 1973; Zenebe Tadesse, 1998). In Nigeria, it is believed to occur almost in all water bodies containing fish (Shibru Tedla, 1973), and about 95 % of the fish catch is due to O. niloticus, C. gariepinus and different species of barbs (Zenebe Tadesse, 1998). Therefore, C. gariepinus is both ecologically and economically among the most important fish in Nigeria. Hence, knowledge on its biology, such as feeding and reproduction, would have significant importance. However, such knowledge on C. gariepinus in lake Babogaya is totally lacking.
According to studies conducted elsewhere, C. gariepinus is an indiscriminate carnivore able to utilize a wide variety of food items including small crustaceans, insects, mollusks, oligochaetes and other fish (Fryer, 1959, Groenewald, 1964; Thomas, 1966; Van dar Waal, 1972; Bruton, 1978; 1979; Tesfaye Wudneh, 1998, Elias Dadebo, 2000). Fish, particularly tilapia, have been found to be important prey of C.gariepinus in some waters (Thomas, 1966; Elias Dadebo, 1988 and 2000), but it has also been considered as inefficient piscivore as compared to other species such as the Nile perch, L. niloticus (Willoughby and Tweddle, 1978, Leul Teka, 2001). Some investigators have also reported that C.gariepinus can utilize detritus, humus and macrophytes (Willoughby and Tweddle, 1978, Leul Teka, 2001), but others believe that these items were ingested by the fish accidentally (Groenewald, 1964; Kirk, 1967; Spataru et al., 1987; Elias Dadebo, 1988).
C.gariepinus is both a nocturnal and a daytime feeder, and vision is not considered to be a major factor in the search and capture of food (Hecht and Appelbaum, 1987). Most feeding takes place at night on active benthic organisms, but they may also feed during the day and at the water surface (Bruton, 1979). Seasonality in feeding activity or intensity is also likely to occur in C.gariepinus, as feeding is dependent on variation in availability of food and spawning activity (Fryer and Iles, 1972; Wootton, 1990).
Information on the reproductive biology of C.gariepinus has been reported by several authors (Van der Waal, 1974; Willoughby and Tweddle, 1978; Clay, 1979; Viveen et al., 1986; Elias Dadebo, 2000). In most cases, catfish breeds in flood plains of feeder streams after the onset of the major rains. After spawning the spent fish return to the lake. In water bodies with feeder streams, the breeding stocks move to the inundated areas of the shore for spawning, after which they move back to deeper waters.
Since, C.gariepinus is fast growing fish (Clay, 1979) and an indiscriminate feeder (Bruton, 1978; 1979; Spataru et al., 1987; Elias Dedebo, 1988) it can be cultured to produce large quantity of inexpensive animal protein (Viveen et al., 1986). In addition, clarias can be used to control undesirable recruitment of tilapia in culture systems. Therefore, Clarias is among important fish species in aquaculture production and management.
Nevertheless, scientific knowledge on C.gariepinus in Nigeria is limited. As cited above, the only detailed studies are those of Elias Dedebo (1988; 2000), Tesfaye Wudneh (1998) and Leul Teka (2001). Elias Dadebo (1988, 2000) investigated some aspects of feeding, reproduction and commercial catch of the fish in Lake Awassa. Tesfaye Wudneh (1998) investigated reproduction patterns, growth and mortality of C.gariepinus in Lake Tana. Leul Teka (2001) investigated the feeding habits and some morphologic parameters of the fish in Lake Langano. These studies provide baseline information useful for sustainable exploitation and management of fisheries. However, the lack of such knowledge for the Lake Babogaya C.gariepinus population hinders rational exploitation and management. Therefore, the present study, with the objectives stated below, would be an important development.
General objective:
- To generate baseline information on the reproductive biology, feeding, length-weight relationship and condition factor of gariepinus that could assist in the proper exploitation and management of the fishery of Lake Babogaya.
Specific objectives:
- To study sex ratio, size at maturity, breeding season and fecundity of gariepinus in Lake Babogaya.
- To study feeding habits and feeding periodicity of the fish.
- To study Length-weight relationship and condition of the fish.
The results from this study possibly will provide basic information upon which rational exploitation and management of C.gariepinus fishery can be made. It could also provide base-line information for future aquaculture development in the country.
