Reproductive biology of the female shovel-nosed lobster Thenus unimaculatus (Burton and Davie, 2007) from north-west coast of India

Abstract

Reproductive biology of the female shovel-nosed lobster Thenus unimaculatus from the north-west coast of India was studied from samples obtained from the fishery along Gujarat coast. Development of secondary sexual characters, gonadal maturation, size at sexual maturity, fecundity and Gonadosomatic Index (GSI) were assessed. Development of ovigerous setae on abdominal pleopods and size of gonopore were identified as secondary sexual characters indicative of the maturation state of the lobster. Onset of maturity in females is marked by the development of ovigerous setae. There are no mating windows (ventral sternite region) in female T. unimaculatus. Female reproductive tract in T. unimaculatus comprises of ovaries, oviducts and genital opening. Ovarian development in T. unimaculatus could be classified into six stages - Immature, Early Maturing, Late Maturing/Mature, Ripe, Spawning and Spent/Recovery. The process of ovarian maturation in T. unimaculatus could be traced through three distinct phases depending on the extent of yolk deposition – Pre-vitellogenesis, Primary vitellogenesis and Secondary vitellogenesis. Morphological, physiological and functional maturity is almost simultaneous in T. unimaculatus, with the size at first maturity in females attained at 61-65 mm CL. Size at onset of sexual maturity, judged from the 25% success rate in development of different sexual characters is 51-55 mm CL. Average fecundity for reproductively active females in the size range of 60-102 mm CL is 39300 eggs. Ovarian development corresponds well with the changes in GSI, with maximum GSI values coinciding with the occurrence of mature individuals.