The influence of feeding regime on sexual maturation, fecundity and atresia in first-time spawning turbot

Exposure of adolescent turbot Scophthalmus maximus to low rations during vi tellogenesis, covering the 4 months immediately prior to spawning, led to a drop of 70% in mean ovary weight, and was associated with poor growth of t he vitellogenic oocytes or, in a third of cases, the absence of vitellogeni c oocytes. Exposure to low rations during the recruitment of vitellogenic o ocytes, 4-8 months prior to spawning, produced a more variable response. A few of these females produced well-developed vitellogenic oocytes, but in m ost, vitellogenic oocytes were absent or only poorly developed and in some cases there was a high incidence of atresia. Exposure to intermediate ratio ns throughout oocyte recruitment and vitellogenesis also depressed oocyte d evelopment. In maturing females the number of non-atretic vitellogenic oocy tes (relative potential fecundity) averaged 998 per g of somatic body weigh t of fish at the start of the spawning season in mid-June. Maturation of th e males was not significantly influenced by the dietary regime. The small s ize of the testes and the low levels of milt production, even in fish fed h igh rations immediately prior to spawning, showed that reproductive investm ent in males was much lower than in females. (C) 2000 The Fisheries Society of the British Isles.