SOME IMPLICATIONS OF THE PROBLEM OF AGE AETD GROWTH IN MARINE FISHES FROM THE INDL\N WATERS

Abstract

Growth studies on teleosts from the Indian waters are largely based on length
frequency distribui ion, for the simple reason that age determination from other conventional
metjiods has been found to be diflScult. In some fishes, where scales, otoliths and
other hard parts show clear zonations, it is difficult to conclude that these are formed
annually. In all those species, which breed successively over prolonged periods, length
frequency distribution will not easily indicate yearly broods. Therefore, it has been
suggested that before undertaking the study on growth, some generalized growth
characteristics in tropical fishes should be taken into account. Experimental studies on
fishes, by keeping them in large cages suspended in the sea, has been suggested as one of
the possible approaches for determining their rates of growth. The characteristics of
some of the well-known growth parameters have been described and the various methods
used for estimating the mortality rates of fishes have been indicated. The method
employed by the Indian workers, for estimating the mortality rate, is to change the size
structure of the catch into age- structure and then estimate the total instantaneous
mortality coeflBcient (z) by comparing the abundance offish at successive ages or from their
numbers at successive length groups. From the estimate of z, it is possible to determine
both fishing mortality coefficient F and natural mortality coefficient M. The yield
from a fishery can be determined by employing the two well-known approaches—the
Beverton^Holt approach and Shaefer approach.