The Reproductive Biology of Haddock (Mellanogrammus aeglefinus) at the Rockall Bank

Histological examination conducted on gonads of Rockall haddock showed that asynchronous vitellogenesis of oocytes and batch spawning are typical of this stock. The post-spawning features could be observed in ovaries and testes until September. The maximum values of the gonadosomatic index (GSI) (12.0–19.6%) were found in pre-spawning females (stage IVa) in March–April. In the process of spawning, GSI of females gradually decreased to 0.9–2.4% in May when the last batch of eggs were spawned (stage VI). The minimum values of GSI (0.4–0.8%) were observed during the post-spawning recovery from the end of August to the end of September. The bulk of spawning took place in March–April when 11–19 batches of eggs were spawned. The percent size of an egg batch did not change greatly with age and varied from 5.3 to 9.5% of the total number of eggs found per female. The majority of individuals, at a length of 25 cm at the age of 2 years, become mature. The minimum length of a mature female was 22 cm, and that of a mature male, 18 cm. Absolute potential fecundity (the mean value of individual potential fecundities per age) was 78 thousand eggs in first spawning fish at the age of two years, 340 thousand eggs in four-year-olds, 947 thousand eggs in eight-year-olds.