Recent investigations on the reproductive biology of the haddock, Melanogrammus aeglefinus, of the northern North Sea and the effects on fecundity of infection with the copepod parasite Lernaeocera branchialis

The reproductive biology of haddock, Melanogrammus aeglefinus (L.) from the northern North Sea was investigated during the years 1976 to 1979. There was no evidence that the observed relationship between fecundity and length, fecundity = 0·903 × length3·42, differed from that given by Raitt (1933) for the period 1926 to 1930. The relationship between fecundity and gutted weight was calculated as F = 237 × weight1·13. The percentages of mature fish in age groups I, II, III, IV, V+ were 2, 46, 93, 100. 92 and 0, 30, 80, 94, 100 for males and females respectively. Compared with the period 1926 to 1930 there has been an increase in the percentage of mature 2-year-old females and a reduction in the percentage of mature 2-year-old males. The length at which 50% of the fish were mature was estimated to be 27·5 cm for males and 31·5 cm for females. The fecundity of haddock infected with Lernaeocera branchialis was 21% lower than that of uninfected fish. Although infected fish had significantly lower condition factors than uninfected fish, the difference in fecundity at length between the two groups was mainly attributable to the much lower production of eggs per unit of gutted weight by the infected haddock.