MATURITY, SPAWNING AND FECUNDITY OF THE SPOTTED SEER, SCOMBEROMORUS GUTTATUS, IN THE GULF OF MANNAR AND PALK BAY

Abstract

The ovary of spotted seer passes through 10 finer maturity stages, A to J,
besides a partly spent stage (S) and a quick transitory stage (Q') between stages
G and H. There is only one batch of maturing ova in B to F stage ovaries,
whereas G to I stage ovaries possess two batches. In all, 2.23 batches of ova are
spawned each season, 1 (first), 0.23 (second) and 1 (third) at stages H, I and J,
respectively. Stage C takes 90 days to attain stage G and 112 days to attain
stage H. After spawning the first batch at stage H, the ovary assumes stage S,
which resembles stage D. and takes 92 days to attain stage J for spawning the
third batch. Each adult female thus takes about 204 days to complete the spawning
process. Gonad indices above the value of about 7 to 8 represent maturing
ovaries, whereas those below this value represent immature or intermediate ovaries.
First maturity is attained when the fish is about 400 mm in total length, i.e., when
the age is about 20 months. Spawning extends from January to August, releasing
a weak brood in January-February, a strong brood in March-July (peak in April-
May) and another weak brood in August. Spawning takes place in areas between
20 m and 60 m depth in the northern Gulf of Mannar. The spent adults migrate
to the central Gulf of Mannar coast by November-December. Spawning takes
place around the full-moon period. Females far outnumber (60.2%) males
(39.5%). Although the males are predominant in size groups between 361 mm
and 481 mm, they are scarce or absent in size groups larger than 481 mm,
suggesting early senility and death. No real difl^erence in fecundity is observed
among stages D, E, F and G. The increase in egg number per 10 mm body length
is 34,082, and the fecundity per every ton of spawning female is 359.8 million.