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Abstract

Fish species diversity and abundance across major horizontal flow of Osun River were assessed for information on its fish resources status. Bi-monthly sampling was done from November, 2017 to March, 2018 using monofilament gillnets of meshes 25, 38, 76, 101, 126 and 177mm. Seven sampling zones (A-G) were randomly selected across the length of the river at equidistant of 2 km apart from the headwater to deposition zone of the river. Biological diversity was calculated using Shannon Weiner diversity (H) and Evenness (E) indices. A total of 2850 individuals belonging to 14 species and 8 families were recorded with the monthly relative abundance and diversity of fish species highest in March (23.4%) and November (3.29) respectively. Zone A had the highest total monthly abundance with Chrysichthys nigrodigitatus the most abundant (21.3%). The river was generally low in biodiversity and therefore proper management strategies should be enforced for sustenance of the fish species.

Keywords: Biodiversity, Sustainability, Osun River, Dry season

Abundance and Diversity of Fish Species in Osun River, Nigeria

1 2 Iyiola, A. O* . and Jenyo-Oni, A.1Department of Fisheries and Wildlife Management,College of Agriculture; Osun State University, P.M.B. 4494, Osogbo, Nigeria.2Department of Aquaculture and Fisheries Management; Faculty of Renewable Natural Resources, University of Ibadan

*Corresponding Author E-mail: adams.ovie.iyiola@gmail.com

Fagbenro, O.A.; Ajani, E.K.; Magawata, I.; Shinkafi, B.A.; Ayoola, S.O. and Orisasona, O. (Eds.) (2018) Proceedings of 1st Conference of Association of Nigerian Fisheries Scientists. “Science, Innovation and Aquabusiness: A Tripod for Sustainable Fisheries and Aquaculture Development in Nigeria” July 10-12, 2018 in the University of Ibadan, Ibadan, Nigeria

253

Results

A total of eight families and 14 species was recorded from the study area (Table 1) with Cichlidsae (38.8%) and Distichontidae (0.5%) as the most and least abundant respectively in terms of numerical abundance, C. nigrodigitatus (21.3%) and D. rotratus (0.5%) had the highest and least abundance, respectively (Table 1). The total relative monthly abundance of fish species decreased from Zone A (24.6%) to Zone G (4.6%) with monthly relative numerical abundance increasing from November (16.8%) to March (23.4%) (Table 2). Richness decreased progressively across the months from

Table 1: Relative fish composition and abundance in Osun River catchment

Family/Species Number Number (%)

Total Family

Family (%)

Cichlidae 1107 38.8 Oreochromis niloticus 454 15.9 Sarotherodon galileaus 284 10.0 Coptodon zillii 317 11.1 Red Tilapia 25 0.9 Coptodon marie 27 0.9 Mormyridae 75 2.6 Mormyrus rume 75 2.6 Mochokidae 39 1.4 Synodontis budgetti 39 1.4 Schilbeidae 128 4.5 Schilbe mystus 128 4.5 Alestidae 861 30.2 Alestes baremoze 340 11.9 Brycinus macrolepidotus

213

7.5

Hydrocynus forskalii

308

10.8

Claroteidae

608

21.3

Chrysichthys nigrodigitatus

608

21.3

Latidae

19

0.7

Lates niloticus

19

0.7 Distichontidae

13

0.5

Distichodus rotratus

13

0.5 Total 2850 100 2850 100

Table 2: Monthly relative numerical abundance of fish species in Osun River catchment

Months/Zone A B C D E F G Total Monthly Total (%) November 140 97 69 82 42 29 19 478 16.8 December 115 110 102 76 46 41 21 511 17.9 January 123 149 113 80 57 45 26 593 20.8 February 164 120 112 87 60 35 24 602 21.1 March 158 131 123 86 71 56 41 666

23.4 Total

700

607

519

411

276

206

131

2850

100

Zone total (%)

24.6

21.3

18.2

14.4

9.7

7.2

4.6

100

Fagbenro, O.A.; Ajani, E.K.; Magawata, I.; Shinkafi, B.A.; Ayoola, S.O. and Orisasona, O. (Eds.) (2018) Proceedings of 1st Conference of Association of Nigerian Fisheries Scientists. “Science, Innovation and Aquabusiness: A Tripod for Sustainable Fisheries and Aquaculture Development in Nigeria” July 10-12, 2018 in the University of Ibadan, Ibadan, Nigeria

254

November (14) to February (12) and later increased in March (14) with a combined richness in the catchment at 14. The fish species in the catchment was fairly even with the highest species diversity in the month of November (3.29) and a combined value of 3.25 in the catchment (Table 3).

Table 3: Diversity indices of fish species in Osun River catchment

November December January February March Combined

Shannon weiner (H) 3.29 3.27 3.25 3.24 3.22 3.25

Evenness 1.25 1.28 1.31 1.31 1.22 1.27

Richness 14 13 12 12 14 14

Discussion

The steady monthly increase could be attributed to the reduced water level during the study period which made fish susceptible to the fishing gear (Yem et al., 2011; Lawson and Olusanya, 2010). The abundance (2850) and composition of fish species (8 families and 14 species) recorded from the catchment was low and fairly even in distribution with Cichlidae family dominating the catchment area (Ipinmoroti et al., 2018; Adeosun et al., 2016; Akinyemi et al., 1986). It was observed that Zone A which was located within the Asejire dam area recorded the highest relative numerical abundance (24.6%) and the highest species diversity (3.29) which could be due to the large surface area created by the wall which enabled accumulation of fish species, location and food availability (Yem et al., 2016). The topography created by the river course reduced upstream from Zone G with the least surface area at Zone A and this characteristic transcended to a decrease in relative-numerical abundance of fish species across Zones G to A notwithstanding factors such as migrating, water level fluctuations, temperature and humidity (Lawson and Olusanya, 2010). These factors have been reported to cause a reduction in diversity of fish species of Lake Victoria and Lake Chad as a result of reduction in size of lakes (Ogutu-Ohwayo, 2005). The information statistic index presented from Shannon Weiner index (H) expressed a low species Richness (14) when compared with rivers within the region and high in diversity (H = 3.25) and a fairly distribution of fish species in the catchment area (1.27). The low species richness and abundance might be as a result of the negative effects of the presence of predators (Gratwicke et al. (2003) and factors such as unregulated fishing, pollution and climatic factors (Ipinmoroti, 2013). The high diversity explained the abundance of fish species because the more diverse a system is, the better it can withstand stress from the environment making it more productive (Taiwo, 2010).

Conclusion

It is evident from the results that the fisheries’ resources experienced monthly increased fluctuations as the dry season progresses and across the zones which was as a result of the differences in size of river course. The low abundance and richness may be as a result of the presence of predators, pollution, unregulated fishing, climatic conditions and introduced species. Strict adherence to environmental laws and fishing practices for sustenance of the resources is utmost.

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FI AN IRE SHG EI RN F IESO N S

COI IT E

A NI TC ISO TS SS A ANIFS2018Proceedings of the 1st Conference and Annual General Meeting “

” July 10-12, 2018 in the University of Ibadan, Ibadan, Nigeria

Science, Innovation and Aquabusiness: A Tripod for Sustainable Fisheries and Aquaculture Development in Nigeria

Fagbenro, O.A.; Ajani, E.K.; Magawata, I.; Shinkafi, B.A.; Ayoola, S.O. and Orisasona, O. (Eds.) (2018) Proceedings of 1st Conference of Association of Nigerian Fisheries Scientists. “Science, Innovation and Aquabusiness: A Tripod for Sustainable Fisheries and Aquaculture Development in Nigeria” July 10-12, 2018 in the University of Ibadan, Ibadan, Nigeria

FI AN IRE SHG EI RN F IESO N S

COI IT E

A NI TC ISO TS SS A ANIFS2018Proceedings of the 1st Conference and Annual General Meeting “

” July 10-12, 2018 in the University of Ibadan, Ibadan, Nigeria

Science, Innovation and Aquabusiness: A Tripod for Sustainable Fisheries and Aquaculture Development in Nigeria