STUDIES ON THE AGE AND GROWTH OF SANDWHITING SILLAGO SIHAMA (FORSKAL) FROM PULICAT LAKE WITH OBSERVATIONS ON ITS BIOLOGY AND FISHERY

Abstract

With the help of otoliths the age and growth rate of Sillago sihama were
estimated, von Bertalanffy's growth equation for this species can b; axpressed as
406.82 fl-e'^'^^^^ (1-0.2745)1.^)^2 length-weight relationships for juveniles and
adults followed the cube law. The slope of the two growth stanzas did not show
significant difference, but the elevation showed at 5% level. A steep fall in condition
factor from 65 mm to 105 mm and peaks at 140-145 mm and 205-225 mm
length ranges were seen which correspond to change in the feeding habit of the
fish, onset of maturity and 50% level of full maturity respectively. 'K' values were
higher during July-February and low during March-June. Sex ratio was studied in
relation to size, space and seasons using x^ test. Fully mature and oozing specimens
were recorded during June-August and December-February in large numbers. This
species attains first maturity at about 225 mm in total length (50% level). Spawning
season seems to be prolonged with two peaks in a year during June-September
and December-February. The fecundity of this species measuring 227-313 mm
in length varied from 31,678 to 2,88,000 with a mean of 1,56,711. Handlines with
polychaete worms as bait account tor nerly 90% of the fish captured from the
lake. Annual catch of S. sihama from I-ake Pulicat varied from 21.7 to 35.6 tonnes
during the years 1965-1969. For this fish, postmonsoon (Jan^Mar.) is the most
productive period, followed by pre-monsoon (Jul.-Sep.) and summer (Apr.-Jun.);
monsoon (Oct.-Dec.) is the lean season