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This study provides new and practical information to implement the use of photoperiodic manipulation for the control of the sexual maturation of Canadian 6+ Atlantic wolffish (Anarhichas lupus) and 3+ first-time spawners spotted wolffish (Anarhichas minor) from Canadian and Norwegian populations. Wolffish reproductive cycle (gametogenesis and oocyte maturation and spermiation) was monitored for 23 consecutive months. Control groups were held under a 12-month simulated natural photoperiod and treatment groups under an 8-month compressed photoperiod. Plasma sex steroid concentrations (estradiol-17β and 11-ketotestosterone), oocyte diameter growth, and milt production were assessed monthly. For all groups under study, fish subjected to the compressed photoperiod spawned 2–6 months earlier than the controls. Complete out-of-shift cycle was not achieved based on the completion of two reproduction cycles, and this is briefly discussed. Photoperiod treatment induced temporal shifts in sex steroid profiles, which are the likely mediators of altered timing of ovulation/final maturation. Photoperiod has a strong influence on the timing of wolffish maturation and could be used as an efficient and inexpensive tool to secure wolffish reproduction operations (year-round supply of egg and milt and/or timing with optimal temperature regimes).

This study contributes to the identification of an adequate cryopreservation medium for wolffishes sperm (Anarhichas minor and A. lupus). Our results also confirm the presence of antifreeze proteins in the seminal fluid of the Atlantic wolffish (Anarhichas lupus) that could facilitate the process of cryoconservation in association with increased post-thaw motility and fertilization rates. Cryo-Fish, a commercial diluent was the most efficient in our trials, with 80% motility post-thaw.

Full scale experiments in tanks were conducted to elucidate the effect of photoperiod regime, dietary fat level and stocking density on growth in spotted wolffish. The study showed that continuous light (LD24:0) did not give a higher final mean weight or faster overall growth rate in spotted wolffish compared to constant 8 h light and 16 h darkness (LD8:16). However, there were indications that the fish needed time to adapt to a new photoperiod regime. The feeding experiment indicated a negative relation between dietary fat level and growth, where fish given 15% fat in the diet had a 13% higher final mean weight compared to fish on a diet with 20% fat. However, no conclusions could be made. The final mean weight was 10% higher at 25 kg/m2 compared to 40 kg/m2, indicating a negative impact of high stocking density on spotted wolffish.

Eggs of spotted wolffish (Anarhichas minor Olafsen)were incubated at constant 4, 6 and 8 °C, and disinfected withglutaric dialdehyde (150 p.p.m. for 5 min) once ortwice a month during two thirds of the incubation period, to prevent growth ofmicroorganisms. Hatching of apparently normal larvae started earlier when eggswere disinfected twice a month compared to once a month at all incubationtemperature regimes. The time to 50% hatch was 900 and 920 day-degrees (16 and16,5 weeks) at 8 °C, 835 and 880 day-degrees (20 and 21 weeks)at 6 °C and 725 and 800 day-degrees (26 and 28,5 weeks) at 4°C, in the egg groups disinfected twice or once a month,respectively. The best survival until hatching was noted when eggs weredisinfected twice a month and incubated at 6 and 8 °C.Survivalwas very low at 4 °C. Prematurely hatched larvae wereregistered in all egg groups disinfected twice a month and the highestfrequencywas noted in the 8 °C groups. The larval weight at normalhatching in the 6 and 8 °C groups was negatively correlatedwith incubation temperature and intervals of disinfection during the incubationperiod, but after 42 days feeding with live feed (unenrichedArtemia) the weights of the larvae were not significantlydifferent. The specific growth rates of the larvae from the eggs incubated at 6°C and 8 °C were 3.0% and 3.2%, respectively.The mean survival of larvae was between 88% and 96% at 42 days post-hatching.Young wolffish originating from the 6 °C incubation groupsshowed lowest mortality.

The effects of temperature on the survival, growth rate and growth efficiency of larval and juvenile common wolffish, Anarhichas lupus L. were studied at 0–31 days and 9–12 months post-hatching, respectively. The influence of temperature regime during egg incubation on subsequent survival and growth was also examined. The fish were reared at constant water temperatures of 5, 8, 11 and 14°C, and all groups were fed dry pellets. At age 1 month, maximum growth rates were observed at 11 and 14°C. Growth rates and survival of early juveniles were dependent upon incubation history, high growth being obtained only if rearing temperature exceeded the temperature of egg incubation. In juveniles at age 9–12 months, the relationships between temperature and growth, and temperature and growth efficiency were parabolic: the optimum water temperatures for growth (Topt.G) and growth efficiency (Topt.GE) were 11°C and 9.7°C respectively. The growth rate and growth efficiency at these water temperatures were 0.9% day–1 and 0.45 g weight gain per g food offered, respectively. © Rapid Science Ltd. 1998

Mortality of artificially fertilized, laboratory incubated eggs of common wolffish,Anarhichas lupus L., was 100% within 2–3 weeks, at the gastrulation step. The eggs from batches with a high proportion of normally cleavaged eggs died later than the eggs from batches with a low proportion of such eggs. Light micrographs of egg shells showed ulceration of the outer layer and subsequent destruction of the inner layer of zona radiata, caused byFlexibacter sp. The bacterial infection provoked premature hatching at later stages of embryonal development. Treating eggs with glutaraldehyde at a concentration of 600 mg l−1 every third to fifth day during incubation prevented the mortality caused by bacteria.

Peculiarities of reproduction, early ontogeny, methods of egg incubation, and influence of temperature on development are compared in wolffish (Anarhichas lupus L.) and in salmonids, mainly Atlantic salmon (Salmo salar L.). Reproductive indices of females are similar in both species, but differ in males due to the small production of sperm in wolffish, a difference explained by internal fertilization in the latter species. The rate of embryonal development until the beginning of differentiation of fin fold at the same temperature is similar in both species, but the period from activation to hatching is more than twice as long in wolffish as in Atlantic salmon. Wolffish hatch at a more advanced stage with a small remnant of yolk sac and begin to feed shortly thereafter. As in Atlantic salmon, eggs and larvae of wolffish have a wide range of temperature resistance except before and after hatching. Based on the difference of life cycles in wolffish and salmon, technologies for their artificial breeding are compared.