Abstract
Length-weight relationship and condition factor have severalapplications on fish biology, physiology, ecology and fisheries assessment. A six-month study was conducted from November 2013 to April 2014 to determine the length-weight relationship and condition factor of four major cichlids namely Oreochromis niloticus (Nile tilapia), Hemichromis fasciatus (Banded jewelfish), Sarotherodon galilaeus (Mango fish) and Tilapiazillii (Red-belly tilapia) to fill a knowledge gap and provide useful information for fisheries management and conservation in the Golinga reservoir using the length-weight based model. Samples were collected twice every month with gillnets from commercial fishermen. The length-weight relationship had a strong positive correlation (r>0.8) for the four species. Oreochromis niloticus exhibited isometric growth (b = 3.07) whilst Hemichromis fasciatus (b = 2.81), Sarotherodon galilaeus (b = 2.91) and Tilapia zillii (b = 2.75) showed negative allometric growth. Mean condition factor (K) values were greater than one (3.66-4.88) for all the species and varied monthly. The study provided new information on length-weight parameters for the four cichlids.
Highlights
The natural fishery resources in Ghana are declining (Ofori-Danson et al, 2012), so there is a need to considerably increase fish production through strict management measures to bridge the widening gap between demand and supply
The standard Length (SL) of O. niloticus ranged between 6.2 cm and 19.0 cm and weighed between 5.1 g and 225.00 g; Standard Length (SL) of H. fasciatus ranged between 5.0 cm and 12.0 and weighed between 9.0 g and 76.0 g
An exponential relationship was revealed between the Standard Length (SL) and body Weight (W) of O. niloticus, H. fasciatus, S. galilaeus and T. zillii and the equations describing these relationships were W = 0.035L3.073(r = 0.889), W = 0.129L2.554(r = 0.938), W = 0.061 L2.908 (r = 0.975) and W = 0.0808 L2.753 (r = 0.959) respectively Fig. 1-4
Summary
The natural fishery resources in Ghana are declining (Ofori-Danson et al, 2012), so there is a need to considerably increase fish production through strict management measures to bridge the widening gap between demand and supply. According to Le Cren (1951), knowledge of the length weight relationship of a fish is essential, since various important biological aspects, viz, general well-being of fish, appearance of first maturity, onset of spawning, etc., can be assessed with the help of condition factor, a derivative of this relationship. The length-weight of fish is an important fishery management tool because it allows the estimation of the average weight of the fish of a given length group by establishing a mathematical relationship between the two (Beyer, 1987). As length and weight of fish are among the important morphometric characters, they can be used for the purpose of fish stock assessment. The objective of study was to generate current information on the length-weight relationship and condition factor of major cichlid species for sustainable exploitation and management of the Golinga reservoir fishery
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