First report of intersex in Cobia, Rachycentron canadum reared in Gulf of Mannar, India—A case study

Abstract

The present study reports the first incidence of intersex in Cobia, Rachycentron canadum maintained at sea cages in the Gulf of Mannar, India. During the 10 year study period (2010–2019), at total of 815 broodstock (386 wild captured and 429 captive raised) were maintained under captivity in sea cages in the Gulf of Mannar, India for the purpose of seed production. Of which, 318 male and 252 female broods’ gonads were examined post-mortem following a natural death. Only one male fish was found with a visible gonadal anomaly. Microscopic analysis of gonad revealed the presence of both the characteristic female and male tissues in testes of a single specimen (testis-ova). Only the abnormal nodular portion contained primary oocytes, whereas the central testicular tissue contained spermatocytes and spermatids in the seminiferous lobules. This is the first reported intersex of cobia from the Gulf of Mannar, India. It could be interpreted as low-level rare incidence of natural aberration.