Amino acid composition of three species of Nigerian fish: Clarias anguillaris, Oreochromis niloticus and Cynoglossus senegalensis

2 Abstract: This paper provides information on the diets of Oreochromis niloticus and Sarotherodon galilaeus in Ero reservoir. Fish species were procured from fishermen every fortnight using gill nets, cast nets, traps, hooks and lines. Specimens were chilled with iced blocks at the point of collection and transported to the laboratory. 494 fish specimens were examined and their stomach contents analyzed. Frequency of occurrence and numerical methods were employed in this study. The result of the analysis showed that O. niloticus and S. galilaeus fed on similar food items. These were mainly macrophytes, Chlamydomonas species and Spirogyra. Other food items include detritus, sand grains and insect parts. Thus both species are omnivorous and occupy the same ecological niche.

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Food and Feeding Habits of Oreochromis niloticus (L.) and Sarotherodon galilaeus (L.) in a Tropical Reservoir

Background and aims: Fishes are the main animal protein source for human beings and play a vital role in aquatic ecosystems and food webs. Fish identification can be challenging, especially in the tropics (due to high diversity), and this is particularly true for larval forms or fragmentary remains. DNA barcoding, which uses the 5′ region of the mitochondrial cytochrome c oxidase subunit I (COI) as a target gene, is an efficient method for standardized species-level identification for biodiversity assessment and conservation, pending the establishment of reference sequence libraries.Materials and methods: In this study, fishes were collected from three rivers in southeastern Nigeria, identified morphologically, and imaged digitally. DNA was extracted, PCR-amplified, and the standard barcode region was bidirectionally sequenced for 363 individuals belonging to 70 species in 38 genera. All specimen provenance data and associated sequence information were recorded in the barcode of life data systems (BOLD; w...

https://www.tandfonline.com/doi/pdf/10.3109/19401736.2010.536537

DNA barcoding discriminates freshwater fishes from southeastern Nigeria and provides river system-level phylogeographic resolution within some species

The silver catfish, Chrysichthys nigrodigitatus (Lacepede: 1803) is a highly valued food-fish included among the dominant commercial catches exploited in major rivers of Africa. To provide useful biological data for management, samples were collected monthly between January (2005) and December (2007) in three zones: I: Upper Cross River (grassland), II: Middle Cross River (mixed forest and grassland), and III: Lower Cross River (rainforest)) along 200 km length of the Cross River, Nigeria. Data from 1 248 specimens were processed using: allometric coefficient (b), gonado-somatic index, Fulton's condition factor and diversity indices. Male dominance was observed in all populations; C. nigrodigitatus reached maturity at 11.5cm (male) and 16.7cm (female) total length. Gonado-somatic index was higher for females with a peak in the early rains. The breeding period was between April and August with mean fecundity ranging between 4522 ±1924 eggs and 20321 ± 5543 eggs. This was directly related to total length and weight by the regression models: F = 2365.88 + 560.22 log L and F = 5025.81 +56.34 log W respectively. Exponential equations for length-weight relationships were Wt=- 1.997 Lt 2.206 (Zone I), W = -2.831 Lt 3.040 (Zone II) and Wt= -2.245 Lt 2.995 (Zone III). The mean allometric coef- ficient (b) showed significant departure from cubic value (negative allometry) for Zone I while Zones II and III showed no difference, indicating isometry. Dominant items in the diet were fish and fish parts constituting 21.6% with Food Richness and Gut Repletion Index of 18 and 100% respectively, in all zones. Diet Breadth of 0.802 (Zone I), 0.922 (Zone II) and 0.910 (Zone III) indicate a high trophic flexibility that enables switching from one diet to another according to availability. Mean condition factor for males varied from 0.718 ±0.117 minimum in Zone I to 0.996 ±0.062 maximum in Zone III. Forest inland wetlands (Zone II and III) of Cross River provided better condition for C. nigrodigitatus. Rev. Biol. Trop. 56 (4): 1785-1799. Epub 2008 December 12.

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Diet, size and reproductive biology of the silver catfish, Chrysichthys nigrodigitatus (Siluformes: Bagridae) in the Cross River, Nigeria

Five diets with crude protein of 40% were formulated with different inclusion levels of ethanol extract of Garcinia kola seeds. D1 (control) has 0 g/kg of the extract, while D2, D3, D4and D5 has 0.25, 0.5, 1.0 and 2.0 g/kg of the ethanol extract of G. kola seeds. The weight, fecundity and egg size of Clarias gariepinus were investigated. There was significant difference in the weight gain of the fish at the end of the study. Fish fed with dietary D4 gained the most weight. The lowest weight gain was obtained in fish fed with dietary D1. Similarly, there was a significant difference in the fecundity of the fish fed with different inclusion level of ethanol extract of G. kola seeds. The eggs diameter increased with dose of ethanol extract in the diet fed to the experimental fish. Histological examination showed dose related increase in the alteration and degenerative changes such as cytoplasm shrinkage, rupturing of cell membrane and different vacuole sizes. The results of the study has shown that the ethanol extract of G. kola seeds possesses promising profertility property which can be exploited in fish seeds production.

A. Raji

Papers

Field guide to Nigerian freshwater fishes