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The recent collapse of the Northwestern Atlantic cod fisheries has coincided with a cooling of water temperatures. During this time the condition factor of cod has been poor. The objective of the present study was to determine the effects of long-term temperature acclimation on growth reproduction and thyroid function in laboratory held Atlantic cod (Gadus morhua). One of the key parameters used to assess thyroid function is the peripheral metabolism of L-thyroxine (T4) by microsomal deiodinase enzymes. Deiodinase function has not been described for gadid fish. T4 outer-ring deiodinating activity (apparent K(m) 1-2 nM) was confined primarily to liver. Its properties resembled those for hepatic T4ORD activity of other teleosts and the mammalian type II deiodinase. The T4ORD activity of cod liver exceeded that of salmonids and could explain the high plasma T3 levels (10-18 ng/ml), which were 2-5 times greater than T4 levels. T4 and T3 inner-ring deiodination was confined mainly to brain. In order to determine the effects of long-term temperature acclimation on cod, somatic growth, reproduction, and thyroidal status were assessed monthly in 400-900-g satiation-fed male Atlantic cod captured in June from the St. Lawrence Estuary and then acclimated from August to the following June under a natural photoperiod at 2-4 degrees C (LT) or 6-10 degrees C (HT). Reproductive status was determined from the gonadosomatic index (GSI), plasma testosterone (T) and 11-ketotestosterone (11-KT) levels, and the appearance of milt; thyroidal status was determined from plasma T4 and 3,5,3'-triiodo-L-thyronine (T3) levels and hepatic T4ORD activity to produce biologically active T3. Testis maturation (high levels of 1 and 11-KT, and milt release) occurred in April and May and was uninfluenced by acclimation temperature. LT cod grew more slowly than HT cod. Differences in body weight were particularly evident from December to February. In conclusion, (i) cod possess outer- and inner-ring deiodinase activities, predominating respectively in liver and brain, and with properties resembling those of other teleosts, (ii) T4ORD activity of liver is unusually high and may account for the high plasma T3 levels in this species, (iii) T4ORD activity tends to increase during periods of increased somatic growth, and (iv) chronic acclimation of male cod to 2-4 degrees C, as opposed to 6-10 degrees C, decreases somatic growth but does alter circulating levels of thyroid hormones and androgens and it does not change the time of sexual maturation.

Flounders (Pleuronectiformes) from eastern North America have been extensively studied over the last few decades, and most of that work has been oriented towards different aspects related to fish production, i.e., aquaculture. However, aquaculture production has not progressed as it might have been expected. Flounders are omnivorous, euryhaline, inhabit shore habitats, and offer good potential for aquaculture diversification. They are found all along the eastern coast of Canada and the US, and different species occupy coastal habitats with some species overlapping in certain areas. Despite specific biological and ecological requirements for each species, the accumulated knowledge on breeding, larval rearing, juveniles, and stock enhancement creates a frame of reference that is often underestimated but that indicates a promising future for the production of these fishes. [ABSTRACT FROM AUTHOR]

Brook trout (Salvelinus fontinalis (Mitchill, 1814)) supports a lucrative fish aquaculture industry in Quebec and production of this species is mainly oriented to stock enhancement supporting sport fisheries. The aim of this study was to verify the expression of interstrain heterosis, i.e., increased performance of first generation hybrid progeny, during the first stages of development in brook trout. Two wild populations that were recently introduced to fish production in Quebec, the Laval (L) and the Rupert (R) strains, and a domestic strain (D) that is present in most Quebec fish farms were used in this study. The growth of 72 full-sibling families, representing three pure (♀D × ♂D, ♀L × ♂L, ♀R × ♂R) and five hybrid (♀D × ♂L, ♀D × ♂R, ♀L × ♂D, ♀L × ♂R, ♀R × ♂L) cross types, were surveyed from hatching to 2136 degree-days. Both heterosis and outbreeding depression were observed, depending on the hybrid cross type. The occurrence of heterosis was dependent on the developmental stage, and growth advantage at a very early developmental stage did not necessarily translate into bigger size later on. Outbreeding depression in growth (mass or length) was much less common than heterosis, and when occurring, it varied from 9.2% to 33.3% compared with 9.0% to 88.2% improvement in growth traits for heterosis. The results indicate that in early development, there was higher occurrence of heterosis relative to fish mass than to fish length and that, overall, the occurrence of heterosis was unpredictable. L'omble de fontaine (Salvelinus fontinalis (Mitchill, 1814)) est une espèce très importante au Québec, aussi bien dans le domaine de la pêche que dans celui de l'aquaculture et la production aquacole est principalement axée vers l'ensemencement. L'objectif de notre étude était de vérifier la présence d'hétérosis, soit une augmentation de performance durant les premiers stades du développement chez les hybrides de première génération, lors de croisements inter-souche d'ombles de fontaine. Trois souches ont été utilisées, soit une souche domestique (D), largement utilisée dans les piscicultures québécoises et deux populations sauvages récemment introduites dans le cheptel aquacole, soit la Laval (L) et la Rupert (R). Nous avons étudié la croissance de 72 familles de type plein-frère, représentant 3 croisements purs (♀D × ♂D, ♀L × ♂L, ♀R × ♂R) et 5 croisements hybrides (♀D × ♂L, ♀D × ♂R, ♀L × ♂D, ♀L × ♂R, ♀R × ♂L), de l'éclosion jusqu'à 2136 degrés-jours. De l'hétérosis et de la dépression de croisement ont été observées chez différents croisements hybrides. La présence d'hétérosis était dépendante du stade de développement et une bonne croissance à un jeune stade de développement ne se traduisait pas nécessairement par une taille plus importante lors des stades suivants. Lorsque présente, la dépression de croisement se traduisait par des baisses de croissance (masse ou longueur) entre 9,2 % et 33,3 %, alors que dans le cas d'hétérosis, des améliorations des traits de croissance variant de 9,0 % à 88,2 % ont été observées. Ces résultats montrent une présence accrue d'hétérosis durant les premiers stades du développement en fonction de la masse plutôt que de la longueur des poissons et ils illustrent dans leur ensemble l'imprévisibilité de l'occurrence de l'hétérosis chez cette espèce. [ABSTRACT FROM AUTHOR]

Abstract The effects of temperature and salinity on the reproductive success of Arctic charr, Salvelinus alpinus (L.), were examined by holding broodstock under the following conditions from mid-May until the end of September: fresh water at ambient temperature (NFW; 8–16 °C); salt water (25–30‰) at ambient temperature (NSW; 4–10 °C); fresh water cooled to saltwater temperature (CFW; 4–10 °C); or salt water heated to freshwater temperature (HSW; 8–16 °C). The relative fecundity of females was similar among groups (P > 0.05; 2685 ± 706 eggs), but females reared in NSW produced significantly larger eggs than those raised in NFW. The highest spermatozoa concentrations were found in milt from males reared in SW and the highest milt glucose concentration was from males kept under coldwater conditions (CFW, NSW). Eggs from NSW and HSW females contained more proteins than eggs produced by NFW females. Eggs from NSW females also contained 40% more lipids than was observed in the other groups, and total energy content was 27% higher in eggs from NSW females than in eggs from NFW females. When FW was cooled (CFW), females produced eggs with protein contents similar to those in NSW, but the lipid contents remained 30% lower. Finally, the best survival at the eyed stage and at hatch was observed in families produced by NSW broodstock. Intermediate values were observed in families from NFW or CFW while the highest mortality occurred in families from the HSW group. All these results suggest that, under the experimental conditions used in the present study, coastal seawater conditions offered the most favourable summer rearing conditions with respect to the reproductive success of Arctic charr. [ABSTRACT FROM AUTHOR]