The age and growth rate of rainbow sardine Dussumieria acuta from Mandapam area and its age group composition in the fishery

Abstract

The age and growth rate of Dussumieria acuta of the Gulf of Mannar and the Palk Bay, during April 1969 to March 1971 was studied. According to the Peterson's method of length frequency analysis the fish grows to a total length of73 mm, 95.5mm andll3 mm at the endoflst, 2nd and 3rd quarters of an year and to 128 mm at the end of 1st year, resulting an average growth rate of 10.75 mm per month. Results of the Probability Plot technique of Cassie (1954) applied to the data, showed perfect agreement with those of Peterson's method. Von Berfalanffy's growth equation was fitted and the estimated values of the growth parameters were: Loo = 191 mm, K = 0.20701 and to = -1.34 quarters. Theoretically the fish grows to a length of 128.05 mm, 163.28 mm and 178.91 mm at the end of 1st, 2nd and 3rd years. No growth rings were traceable on the otoliths, but a straightline relationship could be noticed between the lengths of otolith and the fish. The growth by weight showed that the optimum age for exploitation of D. acuta is when the fish is 1 to 11 years old. A study of the age composition of D. acuta in the commercial catches during 1969-71 showed that in the shore seine and the gill net catches 1-year group dominated, whereas in the trawl net catch the O-year class dominated during 1969-70 and 1-year class during 1970-71.