GROWTH RATES OF THE SARDINES, SARDINELLA ALBELLA (VAL.) AND S. GIBBOSA (BLEEK.), IN THE MANDAPAM AREA

Abstract

The monthly mean lengths of the 0-year-classes of S. albella and 5'. gibbosa were
estimated for the Palk Bay seasons of 1952-56. They indicated that, for the greater part
of the Pallc Bay season, the length of each species increased at a decreasing rate. But
towards the end of the season it appeared to increase at an increasing rate. The von
Bertalanffy equation was litted to the former part, the growth curve so obtained was
extrapolated to the latter part of the season also, and the observed and expected mean
lengths were compared. It was seen that the differences in the rate of change of the
monthly mean lengths between years were statistically non-significant.
The asymptotic maximum lengths of the two sardines, estimated on the basis of
the growth data of the first 6-7 months of life are considerably less than the modal sizes
attained by them at the end of the first year of life, indicating that a change in growth
rate has to take place if these modal sizes are to be attained. This expectation is supported
by the observation that the mean lengths towards the end of the Palk Bay season
are larger than those expected on the basis of the growth data of the earlier months and
indicate the start of an exponential phase of growth. Hence there appears to be a periodicity
in the growth of these young fishes, comparable to what is observed in temperate
water fishes. The environmental data also indicate that a change in the growth rate
towards the end of the Palk Bay season is possible.
The estimated monthly growth coeflScients of the two species compare very well
with each other and also with that of the Japanese sardine.