Abstract
Study was carried out to determine some aspects of the biology of Distichodus rostratus (GUNTHER, 1864) in River Rima, North-western Nigeria. This is with a view to provide information on the species in River Rima which has not been documented elsewhere. These include morphometric measurements, growth pattern, diet composition, gonad maturation stages, gonadosomatic index (GSI) and fecundity of the species. A total of 66 samples were collected from Kwalkwalawa fish landing site of River Rima between July and December, 2012. Total length of the samples ranged from 18.70±0.99SE to 46.20±0.99SE with a mean value of 31.18±0.99SE while total weight ranged from 104.20±32.65SE to 892.60±32.65SE with a mean value of 473.92±32.65SE. The b values of 2.461, 2.476 and 2.292 for all samples, females and males respectively indicate negative allometry. Mean condition factor was 1.52±0.517SD, indicating that the species are in good condition. Analysis of the stomach contents revealed that the species are herbivorous feeding mainly on leaves and roots of aquatic plants, grasses, algae and deadwood. Observation of the structural feeding adaptations such as the sub-inferior mouth, the fine and numerous gill rakers, the U-shaped stomach and the long intestine further confirms the herbivorous nature of the fish. Four stages of gonad maturation were established in females and three stages in males. Gonadosomatic index values for males ranged from 0.08 to 1.20% with mean value of 0.25±0.0211SE and for females 0.25 to 2.29%, with a mean value of 1.89±0.829SE. Fecundity ranged from 2,980 – 21,010 eggs.
Highlights
Distichodus rostratus, commonly known as the grass eater, belongs to the Family Distichodontidae
The largest had a total length of 46.2cm and total weight of 846g while the smallest measured 20.2cm (TL) and total weight of 322g
The result of this study shows that D. rostratus is purely herbivorous, feeding mainly on aquatic plants, algae and some dead wood and this is in accordance with the findings of Bakare (1968) from River Niger; Medani (1968) from Jebel-Aulia Reservoir in Sudan; Motwani and Kanwai (1970) and Arawomo (1982) both studies from Kainji Lake
Summary
Distichodus rostratus, commonly known as the grass eater, belongs to the Family Distichodontidae. According to Nelson (2006), the species are found in fresh water. The species are among the major exploitable fish species and are widely distributed in Nigeria, NiloSudan, Niger, Volta, Chad and Nile basins (Teugels et al, 1992). Prior to their introduction into artificial lakes, they had colonized artificial lakes from natural riverine habitats (Abowei, 2010). In Nigeria, Distichodus spp are cultured in fish farms and numerous lentic water bodies due to their ability to feed on grasses and weeds (Nwani and Ude, 2005)
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