The Bonny Estuary
INTRODUCTION
Fishery resources are important source of dietary proteins in most coastal communities in Nigeria and the world at large. This may be why, fishers with considerable levels of farming activities have settled close to natural water bodies for food and material supplies. The Bonny Estuary is one of the most important river systems in the Niger Delta, providing nursery and breeding grounds for a large variety of fish. Fishing in the estuary is intense and catch per unit effort is low. Due to the nation’s efforts towards speedy industrialization and other human activities, the river is fast becoming degraded. Fishing is carried out indiscriminately with various traditional and modern fishing gear (Sikoki et. al; 1998).
Pseudotolithus
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It is adequate for many purposes but a more precise and more objective method is desirable in some causes. The most practical way of achieving this with the minimum cost and labour is to calculate a ‘gonad index’. This can be expressed as: Where w = weight for both gonads (g), and L = total length of the fish.
Since the weight of most fish is closely proportional to the cube of the length this gives an index which is approximately proportional to the relative weight of the gonads. For female fish it is also a relative measure of the ova diameter, independent of the length of the fish (Schaefer and Orange 1956).
GONADOSOMATIC INDEX (GSI)
The gonadosomatic index (GSI) is the ratio of ovary weight divided by fish weight or the equivalent (Davies 1956). It can be used to detect hydrated ovaries since the wet weight of hydrated ovaries is two or more times that of other maturity stages. GSI has the inherent problem that; dividing by an expression of body size usually does not compensate completely ("normalize") for the effects of fish size (Vlarning et al., 1982) and for the same reproductive state, small fish usually have a lower GSI than larger fish as this effect increases with maturation of the ovary. In other words, ovary weight increases faster with fish length than does somatic weight (Vlaming et al. 1982; Hunter and Goldberg
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