Studies on the biology of the scads, Decapterus russelli and Decapterus macrosoma at Vizhinjam, southwest coast of India

Abstract

Predominant among carangids, the scads Decapterus russelli and Decapterus
macrosoma, though showed female domination, did not show any significant
divergence in sex ratio. Both the species were found to breed continuously with
two peak spawning seasons. While March to May and November to December
were the periods for D. russelli, the same were between February, June, October
and December in D. macrosoma. When D. russelli males and females attained
first maturity at age 0.91 years (150 and 140 mm total length respectively), D.
macrosoma species attained maturity on reaching 1.05 years (male 158 mm and
females 157 mm). The regression coefficient and Y-intercept of the logarithmic
length-weight relationship were 2.9251; -1.8668 and 3.46231; -3.1139 respectively
for D. russelli and D. macrosoma. The ELEFAN analysis showed L<» and K values
for the two species in the above order as 290 mm; 0.8y' and 257 mm; O.By'. The
von Bertalanffy plot estimated t,, values as -0.044 and -0.0215 respectively. In
the two recruitment pulses observed in both species, June-July and February
corresponded to the peaks in the case of D. russeli, the same in D. macrosoma
being May and August.