Characterization of the growth rate of adult wolffishes Anarhichas minor and A. lupus: Is avoidance of paternal care at the origin of the expression of a sexual size dimorphism?

Sexual size dimorphism (SSD) in wolffishes has never been unquestionably reported in previous fisheries or aquaculture studies. The sex-related growth patterns of 6+Anarhichas lupus and 3+A. minor (Norway (NW) and Québec (QC) populations) were monitored in replicates in a controlled environment over two successive spawning seasons (21 months). Overall growth achieved indicates the expression of male-biased SSD in males of A. lupus, A. minorqc and A. minornw, being 36.2, 34.0 and 19.6% heavier and 9.7 ± 0.3%, 5.8 ± 0.4% and 5.4 ± 0.2% longer respectively. Male and females A. minor of both populations started at 1 kg body weight and males ended up averaging 3.2-3.5 kg. Females from Norway and Canada reached 2 kg and 2.8 kg respectively, indicating a male growth advantage over female and a lessened expression of SSD in the Norwegian population. A. minornw achieved higher final weight and length in comparison to A. minorqc. In captivity, females underwent normal maturation cycles whereas males were free from egg-guarding duties, which most likely contributed to the expression of SSD benefiting males. In the wild, prolonged embryo paternal care duties, coupled with loss of teeth and reduced feeding during incubation, likely offset any substantial growth advantages for males. The observed reduction in female growth and condition factor values coincide consistently with maturation events. Female specific growth rate also showed more pronounced fluctuations, leading to the observation of a significant growth divergence. The sex-specific growth trajectories achieved in captivity are briefly compared with observations from fishery-based growth studies that not once reported conclusive sex differences. Our observations point to the behavioural and environmental sensitivity of SSD and to the rationale of sex control in wolffish cultivation to produce all male stocks and only rear the fastest-growing sex.