A Survey of the Ichtyofauna of Ogbese River, South West, Nigeria

An investigation into the icthyofauna of Ogbese River, south west, Nigeria, was carried out between October 2010-February 2011. A total of 2,700 individual were caught during the study. Nine (9) species belonging to six (6) families were recorded during the period of study. However, six (6) species [Clarias gariepinus; (410), Heterobranchus bidorsalis (508), Oreochromis niloticus (508), Oreochromis niloticus (410), Mormyrus rume(227), Mormyrus macrophythamus (221) and Malapterurus electricus(341)], were dominant specie, Hepsetus odoe and Parachanna obscura were sub-dominant, while Tilapia zillii was rare. Claridae, followed by Mormyridae and Cichlidaewere the most dominant families (33.99%; 16.58%; 15.62%), while Hepsitidae, Channidae and Malapteruridae were sub-dominant. The highest percentage of relative abundance of the various fish species was recorded in October while the least was recorded in February 2011. The results of this survey showed that the river has low fish species composition and abundance, inspite of the size of the river. Considering this fact, there is need for further survey to cover more months. There is also a need to evolve strategies for effective utilization and proper management of the river, for optimum fish production.


INTRODUCTION
Nigeria is blessed with abundance of natural aquatic resources in marine, estuarine and fresh water environments. The numerous fresh water bodies in Nigeria ( Fig. 1), with over 270 fish species, are the richest in fish diversity in West Africa (Tobor, 2002).The distribution of species in fresh water provides information on whether the fish species are pelagic or demersal, which will further inform the choice of fishing gear to be used. The information on habitat and abundance, amongst others, are very vital for fisheries development and management. The description of fish community of water body is important for consideration, not only the spatial, but also the diversity of fish species as well, because such knowledge can enhance the management of water resources.
A number of workers have worked on the fauna of freshwater environment in Nigeria (Achionye-nzehl and Isimaikaiye, 2010; Francis-Arimoro and Robert-Ikomi, 2007; Oso and Fagbuaro, 2004).The present study is a preliminary investigation of the fish fauna of Ogbese river. The objective of the study therefore, is to do a preliminary survey of the fish fauna and their abundance in the river and also know the dominant fish species in Ogbese River, in order to provide a base-line information for further work on the river.

MATERIALS AND METHOD The Study Area
This study was conducted in a stretch of Ogbese river (Fig. 2) in Ado-Ekiti Local Government Area, Ekiti State. Ogbese River lies between latitude and longitude 7° 45N and 5° 30E, within the tropical rain forest of Ekiti State. In terms of fisheries development, there is no stocking of the river, hence, the fish in the river are naturally occurring. The river is laced with farming activities.

Sampling of the Specimens
Sampling was done for a period of five months, between October, 2010 and February, 2011. Data for this study was based on the record of fish caught by local fishermen. The collection of samples was done once in a week from the landing site of the fishermen. The fishermen used different mesh size of set nets (5mm-22mm) and hooks.  The setting of these gears was mostly done in the evenings by 6.00pm and left overnight, till 6.30 a.m. The catches were collected, sorted into species and families on the field, collected into ice coolers and transported to the laboratory, where they were preserved in 40% formalin for further examination.

Fish Identification
Most of the species caught by these fishermen at the river were sorted into various families and counted. The identification was done both on the field by fishermen and in the Zoology laboratory using identification guide (Babatunde andRaji, 1998 andIdodo-Umeh, 2003).

Data Analysis
All fish species collected were counted to determine species abundance. The relative abundance (%) of each species was calculated by the formula of Benechet.al.
=Total Abundance for all species The relative dominance of each species, over the months, was also determined qualitatively on a scale of 1-4 indicating whether the species abundance was dominant, sub-dominant, occasional or rare.

RESULTS AND DISCUSSIONS Ichthyofauna
The fish fauna encountered in Ogbese River and the monthly relative abundance are shown in Table 1. A total of 2,700 individual of 9 species, belonging to six families; Clariidae, Mormyridae, Cichlidae, Hepsetidae, Malapteruridae and Channidaewere recorded in this study.The highest number of individuasland relative percentage abundance,were observed in three families; Clariidae (33.99%), followed by Mormyridae (16.85%) and Cichlidae (15.63%). These three families also had the highest number of species. Hepsetidae and Malapteruridae were sub-dominant, while Channidae was found to be rare.
In terms of the species number (Table 1) Fig. 2 and 3. The clariidae family and H. dorsalis were the dominant family and species respectively, while Channidae family was caught occasionaly and the species Tilapiazillii [Gervais 1848], was rarely caught.
The primary objective of a sampling survey of this nature is to attempt to find out what fish species exist in Ogbese river and perhaps look at the factors governing their abundance. Fish community studies are not generally equivalent to Ichthyocoenoses because the description of any fish community is a biased image arising from the sampling of a group of fishes in a particular environment at a given time. The use of gear and sampling strategies are the usual source of these biases. In River Ogbese, the types of fishing gear used were the same throughout the study period and so gear selectivity cannot be considered as a valid reason for the monthly differences observed. The influence of habitat or water quality variable on fish can determine abundance. Land use and other human activities influence fish species diversity and abundance in water bodies (Victor and Dickson,1998).
The relatively low species composition in this study, compared with other similar studies with high species richness such as Nwadaro (1998) in Orogodo River, Nigeria, could be due to the use of multiple gears in those sites. Allison et.al.(1997) suggested a multiple gear approach as the best way to obtain comprehensive icthyofaunasamples for such studies. C. gariepinusand H. bidorsalisbelonging to family Clariidaewere recorded as abundant species followed by O. niloticus(Cichlidae)and Mormyridae. Ezenwani (2004) also observed similar trend of high abundance of these species in the lower AnambraRiver.  The discrepancy could also be due to the short period of survey that excludes extensive seasonal variation in catch. This study is in agreement with Sikokiet.al.(1998) in terms of numbers of families and species, but vary in kind of species. The highest, monthly relative abundant catch was recorded in October while the least was recorded in January. This is probably due to seasonal variations that determine food organism abundance in slightly rainy October, compared with the dry month of January.
Only nine species were encountered during the period of study. This does not mean that there are no other species in Ogbeseriver. Ufodikeet al. (2001) reported that hooks and net are essential in maximizing fish catch.They may not be encountered due to the type of gear used and the short period of the study, which has not taken care of seasonal variations.

CONCLUSION
The result of this present study has provided base-line information on the icthyofauna ofOgbeseRiver.Like most other water bodies in Nigeria, the river has an enviable potential for fisheries exploitation. Considering its fairly low fish species composition and abundance, there is need for further survey tocovering many months. There is also a need toevolve strategy for effective utilization and proper management of the river for optimum fish production.