Feeding biology and some biological parameters of Nile tilapia (Oreochromis niloticus) and (Bubu) Auchenoglanis occidentalis) (Pisces: Animalia) in Alwero Reservoir, Baro-Akobo Basin, South west Ethiopia

Abstract

The study was conducted to assess feeding biology and some related biological parameters of Nile tilapia (Oreochromis niloticus) and Bubu (Auchenoglanis occidentalis) Longitudinal study were carried out to investigate food type, feeding biology, length-weight relationships and condition factors of the two fish species in the Reservoir. Fish samples were collected during one dry season (March, 2019) and one wet season (July, 2019). A total of 104 and 80 Nile tilapia and Bubu specimens were collected, respectively. Sampling sites were selected based on the accessibility of the reservoir. Fish specimens were collected using gillnets of 12cm, 16cm, 20cm and 24cm stretched mesh sizes. Prior to dissecting the fish samples for the collection of gut samples, morphometric (weight, standard length and total length) measurements of the fish samples were recorded. Gut contents were preserved in 10% formalin solution and transported to Zoological Sciences Laboratory, Jimma University. Frequency of occurrence and volumetric methods were used for analyzing feeding habit of the fish. An index of preponderance was used to assess overall contribution of prey items to the fish diets. Both Nile tilapia and Bubu had omnivorous way of feeding habit, the diet overlap index was 56%, indicating high dietary overlap between the two species. The diet breadth of Nile tilapia (Ba= 0.33) and Bubu (Ba = 0.40) showed that both species were apparently omnivorous utilizing various types of food resources in the reservoir. The feeding habit of Nile tilapia did not show significant difference between seasons, but that of Bubu showed significant seasonal differences on some prey items such as aquatic insects that had 84% IP and 47% IP during dry and wet seasons, respectively. The lines of best fit to TW = aTLb, for log transformed Weight-Total length had the equations of log TW =1.224log TL 1.68(R2 = 0.9) for Nile tilapia and logTW = 122 log TL 0.624 (R2 = 0.26) for Bubu. The mean values of the relative weight index for Nile tilapia and Bubu were 312.5 ± 100.39% (SD) and 1271.5 ± 204.5% (SD) respectively, were also investigated to understand their condition factor. This study is important step towards understanding the food web in Alwero Reservoir and eventually developing a trophic model for use in fisheries management.