The demand for fish is expected to rise substantially by 2020. Although aquaculture must provide much of the additional fish, it remains to be seen whether restored or enhanced capture fisheries can also help fill the projected gap in supply. The key challenges for capture fisheries involve reducing fishing effort, removing excess fishing capacity and building the institutional arrangements needed to restore spawning biomass to more productive levels, and to reverse degradation of the supporting habitats.
This document represents the report and contributed papers from a workshop of the same name. The workshop was comprised of a group of 30 international experts and representatives of the environmental, fisheries and policy development agencies of the countries in the Volta Basin.
To find out if pawpaw (Carica papaya) seeds can induce sterility in male Nile tilapia (Oreochromis niloticus) and to determine if sterility so induced is reversible or otherwise, mature male tilapia of mean weight 40 g were treated for 30 days with a low dose (4.9 g/kg/day) and a high dose (9.8 g/kg/day) of ground pawpaw seeds incorporated into their feed. Fish of similar sizes in the control experiment were fed with feed that did not contain pawpaw seed.
Starting from a small base, aquaculture production in Africa registered annual growth rates equal to or above those in other regions. This expansion was due to significant increases in a few African countries. Increasing demand coupled with rapidly dwindling catches from capture fisheries, the implementation of novel participatory approaches to technology development and transfer, and the emergence of a few successful large-scale tilapia culture operations directed at the export market offer opportunities for further expansion in both the small-scale and large-scale commercial sectors.
Wild (Sanaga River) and domesticated populations of Oreochromis niloticus were compared onfarm and on-station in the Central Province of Cameroon to determine the degree to which genetic deterioration of stocks may have occurred during the process of domestication and subsequent breeding. On-station, average weight at harvest was 284.3 ± 16.2 and 178.1 ± 9.9 g for Sanaga and domesticated populations, respectively. On-station specific growth rate was 0.0660 ± 0.0022 and 0.0555 ± 0.0016 g/day for Sanaga and domesticated populations, respectively.
Mass selection based on mass spawning can present a feasible and low-cost selective breeding scheme. In mass spawning, however, mating is not controlled and a small number of breeding individuals may account for a lafgeproportion of the next geperation, leading to higher inbreeding, decrease in performance of stocks and no response to selection: To understand the mating systems, reproductive and population parameters under mass spawning, we conducted mass spawnings with female to male sex ratios of 1:1,2:1 and 3:1.
In 2002 Japan's contribution to the WorldFish Center has supported research on genetics and aquaculture in Africa. Two projects have benefited especially from this support. Their activities and achievements in 2002 and plans for 2003 are reported.
The economic benefit derived from a genetic improvement program with Nile tilapia (Oreochromis niloticus) was examined from a national perspective. An industry structure was assumed whereby the genetic improvement program is conducted in a nucleus which provides brood stock to hatcheries, which in turn produce fry for farmers to grow out to market size. Discounting was used to express all returns and costs in terms of net present value. The economic benefit (discounted returns minus discounted costs, EB) and the benefit/cost ratio (BCR) were studied for a 10 year time horizon.
This manual is intended as an aid in the transfer of the selective breeding technology developed by the WorldFish Center and its partners. It was based upon experience and material accumulated during the ‘Genetic Improvement of Farmed Tilapia’ (GIFT) project (1988 to 1997). In its development particular attention was paid to the description of key husbandry operations in a sequential manner, using illustrations and photographs. There will be, however, instances in which some adjustment of the GIFT technology to local conditions is required.
Genetic and phenotypic parameter estimates for tagging and harvest body weights were obtained from the F1 base (377 offspring of 59 full-sib families), F2 (1241 offspring of 52 full- and 33 half-sib families) and F3 (1052 offspring of 55 full- and 25 half-sib families) generations of Oreochromis shiranus. The fish were reared in earthen ponds at three different test environments inMalawi, which were high altitude (Chisitu), medium altitude (Domasi) and low altitude (Kasinthula) fish farms.