SPAWNING BEHAVIOUR AND FECUNDITY OF THE INDIAN MACKEREL, RASTRELLIGER KANAGURTA (CUVIER), AT MANGALORE

Abstract

The earliest reference to the fecundity of the Indian mackerel was by Devanesan
and John (1940) who estimated the number of ripe eggs in the mackerel ovary as
94,000. Subsequent work was directed mostly towards finding out the spawning
behaviour of this fish, by the study of the intra-ovarian eggs. Pradhan (1956)
indicated the possibility of the Indian mackerel spawning the eggs in successive batches
over a prolonged period, like its Atlantic counter-part Scomber scombrus (L). Pradhan
and Palekar (1956) described the maturity stages I to VII, based on the external
appearance of the ovary, its size relative to the abdominal cavity, and the range of
ova-diameter readings. However, they have not given any ova-diameter frequency
polygons. Sekharan (1958) studied the ova-diameter frequency in a few ovaries of
the mackerel, ranging in maturity stage from II-III to V-VI, VI-VII and a few spent
ovaries. He stated that his investigation showed a possibility of the mackerel eggs
ripening in batches and of their release in succession. Radhakrishnan (1962),
adopting the method followed by Clark (1934), Prabhu (1956), and Qasim and Qayyam
(1961), studied the ova-diameter frequency seasonally and indicated the possibility
of the mackerel shedding its eggs in batches. Vijayaraghavan (1962) followed a
different procedure. Employing very high magnification, he measured ova with
diameter greater than 0.525 mm. Plotting this frequency with a small size interval
(3.5^) he claims the modes were clearly distinguishable. These modes according to
him were well-defined batches of eggs ripening in succession. Rao (1962) studied
the ova-diameter frequency in maturity stages I-V and VII. However, spawn-ripe
ovary corresponding to stage VI, as he stated, was not obtained in his study.