Assessment of yellowtail kingfish ( Seriolalalandilalandi) reproductive physiology, as a basis for aquaculture development

Abstract

Patterns of gamete development, size at sexual maturity, seasonal changes in gonadal condition and reproductive endocrinology were investigated in the yellowtail kingfish Seriola lalandi lalandi. Samples were collected by commercial and recreational fishers along the East and West coasts of Northern New Zealand, between September 1998 and March 2000. Changes in the size distributions and proportions of oocyte stages during ovarian development indicated multiple group synchronous oocyte development and the presence of all developmental stages of oocytes in mature ovaries indicated a capacity for multiple spawning within a reproductive season. Changes in developmental stages of gametes during testicular development and the presence of all gamete stages (excluding spermatogonia), in partially and fully spermiated males, indicated multiple group synchronous gamete development in males. The smallest mature female was 775 mm fork length (FL), 50% of females reached sexual maturity at 944 mm FL and 100% at 1275 mm FL. The smallest mature male was 750 mm FL, 50% of males reached sexual maturity at 812 mm FL and 100% at 925 mm FL. Gonadosomatic index (GSI) provided a useful basic measurement of gonadal anabolism. Seasonal changes in gonad stage and GSI indicated that S. lalandi lalandi were spring–summer spawners. Blood plasma concentrations of testosterone (T) and 17β-estradiol peaked in females during vitellogenesis, and plasma concentrations of 17α20β-dihydroxy-4-pregnen-3-one (17,20βP) were significantly elevated in females with ovaries undergoing final oocyte maturation. Blood plasma concentrations of 17,20βP did not change with gonadal development in males; however, plasma concentrations of 11-ketotestosterone and T were significantly elevated in partially and fully spermiated males. Blood plasma steroid profiles from natural cycles provide a benchmark to gauge reproductive performance in captive and domesticated fish. This study provides baseline information required for successful reproductive management of S. lalandi lalandi.