Selection for growth of Nile tilapia (Oreochromis niloticus L.) in low-input environments

Abstract

Nile tilapia,Oreochromis niloticus,is one of the most important species farmed in the world and is the mainstay of many resource-poor fish farmers. The majority of its culturing is carried out in semi-intensive systems with a wide array of pond inputs from the farm. These systems are characterized by poor fish growth and low yields. Studies have shown that only a small percentage of the nutrient input in these systems is converted to harvestable products. Efficient breeding programs are needed to improve the overall nutrient use efficiency of fish in low-input fertilized ponds. Selection for improved growth has typically been doneunder favorable conditions often resulting in breeds which demand more resource than can be provided on the traditional fish farms, thus increasing cost of production. In this research, the feasibility of direct improvement of the growth of Nile tilapia in low-input conditions was investigated.

This study demonstrates good prospects for setting up sustainable breeding programs for resource poor tilapia farming conditions without requiring expensive supplementary protein pellets. An experiment on early growth showed that Nile tilapia juveniles can be grown at the same rate with or without supplementary feeds.There was also a substantial heritability and response to selection for body weight at harvest after two generations of selection. We found little scope for selecting for improvement of cold tolerance in juveniles, but that cold tolerance could be improved by prior acclimatization. Body weight was highly genetically correlated with body measurements indicating that when needed, alternative traits for measurement of growth can be used. The high response and short generation times in Nile tilapia indicate that farmers can reap the benefits of genetic improvement at early stages of the program.

This study found significant evidence for genotype by environment interaction indicating that the selection environment can affect the results of selection. Because poverty alleviation and food security are primary goals in the developing world, the initiation and implementation of cheaper breeding programs will ensure that the genetically improved materials are accessible to the rural fish farmer. Selection for improved growth in low-input conditions should be carried out in low-input environments especially because of low cost of inputs. Appropriate breeding goals need to be set-up with the involvement of the local farmers to ensure that the resulting breed meets the requirements of local farmers. To fully benefit from improved breed programs, farmers should also enhance pond water quality and improve fish nutrition.