Growth Performance, Fecundity and Sexual Growth Dimorphism of Oreochromis esculentus and Two Populations of Oreochromis niloticus Under Cage Culture in Kisii County, Kenya

Abstract

The blue growth initiative can be a driver in helping to meet the increased demand for food. Tilapiine fish species, Singida tilapia, Oreochromis esculentus, a fish once prevalent in Lake Victoria and satellite lakes was relished by the local populace of the riparian Counties. Due to factors, such as predation by the Nile perch, Lates niloticus and competition by the introduced and closely related Nile tilapia, Oreochromis niloticus; its population has diminished drastically; hence necessitates for an intervention to ensure its sustainable existence. The main objective of this study was to evaluate the growth, sexual growth dimorphism and fecundity potential of O. esculentus and compare these traits with two populations of Oreochromis niloticus (from Kitaru dam and the County Fish Multiplication and Training Centre - CFMTC) in order to evaluate them for aquaculture. O. esculentus is a near threatened species, however little is known about its growth performance in captivity and potential for aquaculture in order to ensure its conservation. This study was conducted in twelve (12) 1 m3 fish cages installed in a 362m2 production pond. The pond was located at the CFMTC, in Kisii town (S 00o40.308’ E034o46.482’). The first filial (F1) generation of fingerlings of both O. esculentus and O. niloticus were sourced from brood stock from Gesebei and Kitaru dams in Nyamira County together with the Kisii CFMTC. Weight and length measurements of the fish from the two species were measured for a period of eight (8) months from March to November 2015. Samples of the fish were collected biweekly for weight and length measurements. Eggs / fry were retrieved from brooding females and relative fecundity was evaluated. Analysis of variance (ANOVA), regression analysis and Tukey test were conducted using the statistical package Statgraphics Centurion version 17.0. Results indicated that the asymptotic weight of O. niloticus from CFMTC (329.7±5.48 g) and that of O. esculentus (317.7±5.48 g) were significantly higher (F2,2110=61.9, p<0.05) than that of O. niloticus from Kitaru (258.8±5.48 g). The O. esculentus had the highest asymptotic length of 30.5±0.29 cm, followed by O. niloticus (CFMTC) 28.5±0.29 cm and 26.5±0.29 cm for O. niloticus (Kitaru) (F2, 2110=94.36, p<0.05). There was no significant difference in growth performance between the males and the females of O. esculentus in terms of asymptotic length (F1,712=9.17, p>0.05) and weight (F1,712=4.725, p>0.05). There was a significant difference (F1,664=340.4, p<0.05) in asymptotic lengths (L∞) and (F1,664=342.1, p<0.05) weights (W∞) between the males and the females of O. niloticus from CFMTC. Similar observations were also obtained for the males and females in O. niloticus from Kitaru (F1,664=340.4, p<0.05). For the relative fecundity, there was no significant difference (F2,269=0.652, p>0.05) among the slopes, of the three populations. The female and male of the O. esculentus from Gesebei dam had similar performance in both length and weight. This observation suggested that in a given environment, both sexes grow at the same rate and mature at the same size. The female and male of the two populations of O. niloticus (CFMTC and Kitaru dam) had distinct performance for both length and weight. This observation confirms the view that O. niloticus is the most prominent species for culture and that the males on average are superior to female in growth. There was no difference in the relative fecundity for all the treatments. The study showed that the O. esculentus and O. niloticus (CFMTC) had similar performance in terms of weight but not in length in which O. esculentus had greater length than the latter. However, both O. esculentus (Gesebei dam) and O. niloticus (CFMTC) had better performance than the O. niloticus population from Kitaru dam. The males and females of O. esculentus had similar growth performance. All the test fish were able to breed in cages despite the fact they did not have access to a substrate where they could make nests. The study therefore showed O. esculentus is suitable for recruitment into aquaculture as the aspect of either sex performing on par qualifies it as a species for mixed sex culture or monosex of either sex. It is recommended that the recruitment of O. esculentus as an additional species for aquaculture be considered for inclusion in the draft National policies. It is also recommended that the monosex culture of either female or male O. esculentus be considered. Further investigation into the breeding of fish in cages is crucial to identify potential novel approaches to breeding and rearing species Oreochromis for aquaculture purposes.