Groups of maiden or repeat spawning Atlantic salmon were maintained during vitellogenesis in austral autumn at either 14 o C or 22 o C through until April when all fish were transferred to a spawning temperature of 8 o C. There was no difference in body weight within groups for maidens and repeats, with repeats being consistently larger than maidens, no difference in condition factor among groups, but consistently higher gonad weight in repeats than maidens. Gonadosomatic index (GSI) and follicle diameter were suppressed in both maidens and repeats at 22 o C, with the effect being most marked in repeat spawners. Relative fecundity (egg kg-1) determined from ovarian tissue samples also showed depression in repeats at 22 o C. Fish from both age classes held at 22 o C had a higher proportion of atretic follicles. Plasma levels of estradiol-17β (E 2) were strongly depressed in both maidens and repeats exposed to 22 o C throughout autumn but there was some evidence of recovery among maiden fish by late April. A similar effect was seen on plasma testosterone (T) levels. Plasma cortisol levels were generally low and typical of levels in unstressed fish indicating that stress did not account for the inhibitory effects observed Hepatic zona pellucida protein gene expression was significantly inhibited in both maiden and repeat spawning fish reared at 22 °C, but with some evidence of recovery after temperature reduction to 8 °C. Hepatic vitellogenin (Vtg) gene expression was also lower in both maiden and repeat spawning fish exposed to 22 °C and this was accompanied by reduced plasma Vtg levels in maidens, but not repeats at 22 o C. Maidens at 14 o C began ovulating first followed by repeats at 14 o C, then repeats at 22 o C followed by maidens at 22 o C. There was reduced fertility in maidens at 22 o C relative to both maidens and repeats at 14 o C, whereas repeats at 22 o C showed intermediate fertility between 14 o C fish and 22 o C maidens. Survival to the eyed egg stage was highest in maidens at 14 o C, significantly suppressed at 22 o C in maidens, and at intermediate levels in repeats at both temperatures. This suggests that repeat spawning Atlantic salmon may be more robust in the face of thermal insult which combined with their larger size and egg production, could make their use desirable under production situations where there was any threat of exposure to higher than normal temperature.

Fish fillet quality has been shown to be influenced by the level of antioxidants in preslaughter diet. Thus, an experiment was conducted to study the effect of different levels of vitamin E and C on the fillet quality of market-size reared turbot (Scophthalmus maximus). Turbot of a mean initial weight of 347 ± 20 g were divided into four groups and fed commercial turbot diets (60% protein, 12% fat), supplemented with a-tocopheryl acetate (mg kg )1 ) and ascorbyl-2 monophosphate (mg kg )1 ) at the following dietary levels: 500/100, 1000/ 100, 100/1000, 100/100 respectively. Over a dietary supplementation period of 15 weeks, fish were fed to satiation and reached a final mean weight of 916 ± 29 g. a-Tocopherol levels increased significantly (P < 0.001) in tissue (i.e. muscle, liver, heart and kidney) of fish fed diets containing elevated levels of a-tocopheryl acetate. In ice storage, fillets of these fish exhibited significantly lower (P < 0.001) levels of lipid oxidation, and showed significantly less (P < 0.001) colour deterioration (higher hue angle and lower chroma). Elevated dietary a-tocopheryl acetate levels had a negative effect (P £ 0.001) on the concentration of ascorbic acid in muscle tissue. An increase in dietary vitamin C did not have any detectable effect on fillet quality. Prolonged feeding times had a negative effect on lipid oxidation (P < 0.001) and colour deterioration (P < 0.01). These results suggest that increased dietary a-tocopheryl acetate could prevent colour deterioration and lipid oxidation of turbot fillets in retail storage on ice.KEY WORDS

Fish fillet quality may be influenced by the antioxidant level in preslaughter diet. Thus, the effects of dietary a-tocopheryl acetate supplementation and feeding time on the flesh quality of farmed Atlantic halibut Hippoglossus hippoglossus L. were investigated. Halibut of mean initial weight of 312 + 12.3 g were divided into two groups and fed commercial diets, supplemented with different levels of a-tocopheryl acetate at the dietary inclusion levels of 189 and 613 mg kg À1 diet. Fish were sampled after 6,9,12 and 24 weeks. Over the experimental period, they reached a final mean weight of 1320 + 108.4 g. Tissue a-tocopherol of fillet and liver was significantly affected by the levels of a-tocopheryl acetate given with the diets (P < 0.001). In storage on ice, fillets of fish fed the diets high in a-tocopheryl acetate exhibited significantly lower (P < 0.001) levels of lipid oxidation. The colour of fillets in all groups deteriorated slightly, but diet did not affect this process. Halibut fed the supplemented diets for longer periods were better protected against lipid oxidation (P < 0.001) and colour deterioration (P < 0.01) than those fed for shorter periods. However, after 9 days of storage, lipid oxidation levels were still extremely low [< 0.6 mg malondialdehyde (MDA) g À1 fillet], even in fillets of fish fed the low a-tocopheryl acetate diet for a short period preslaughter. Different slaughtering methods tested at the end of the trial showed that percussive stunning can delay the onset of rigor mortis by 8±12 h compared with bleeding of the fish. These results suggest that halibut fillets have enhanced shelf-life stability even at low doses of dietary a-tocopheryl acetate, and that other factors in the antioxidant defence mechanisms of the species might play a major role in the prevention of lipid oxidation.

Recent recruitment declines in important spiny lobster fisheries worldwide have triggered conjecture about negative impacts of anthropogenically induced environmental change on their long-lived planktonic larval life stages. Puerulus larvae are the critical transitional stage between pelagic larval development and coastal juvenile recruitment and may be particularly sensitive to environmental change due to immature cardiorespiratory capacity and exceptional energy demands associated with shoreward migration. We measured Sagmariasus verreauxi pueruli energy metabolism and defined their thermal tolerance, which are considered against published coastal recruitment data and spatially explicit ocean warming scenarios. The upper threshold of the thermal optimum window (upper pejus temperature range) was defined by the temperature optimum for aerobic scope. Within the upper pejus temperature range, pueruli had diminished aerobic capacity for physiological performance and used more of their finite lipid reserves to support an amplified metabolism. Sea surface temperatures at the northern extent of their natural range already reach the upper pejus range, and monitoring settlement data from the wild indicted that fewer puerulus successfully recruit during hot seasons in this area. Our study provides some evidence that physiological thermal tolerance constraints are already limiting postlarval recruitment. Predicted increases in water temperatures for their rapidly warming habitat will amplify the thermal challenge experienced by pueruli and may result in large shifts in lobster distribution and significant re-shuffling of species assemblages, creating challenges for sustainable natural resource management.

The effects of dietary a-tocopheryl acetate supplementation and different slaughtering methods were investigated on the flesh quality of farmed marketsize turbot Scophthalmus maximus (L). Turbot were divided into three groups and fed commercial diets, supplemented with different levels of a-tocopheryl acetate at the following dietary inclusion levels: 72 (100), 547 (500), 969 (1000) (mg of a-tocopheryl acetate kg À1 diet, analytical values with diet codes in brackets). After 5 months, fish (mean weight 1056 + 19.7 g) from each dietary treatment were sampled, applying three different slaughtering methods: (A) bleeding in ice water; (B) thermal shock, no bleeding; (C) percussion followed by bleeding in ice water. The time course of rigor mortis was evaluated, using pH, rigor index and mechanical compression tests. The results showed that the three parameters corresponded very well. Percussive stunning resulted in higher initial post-mortem pH (P , 0.01) and a significantly delayed onset of rigor mortis (P , 0.05). Diet significantly affected shelflife, with fillets from fish fed diets 500 and 1000 having lower TBARS (thiobarbituric acid reactive substances) numbers from day 2 (P , 0.001) and less colour deterioration from day 7 of storage on ice onwards (P , 0.05). These results suggest that an increase in dietary a-tocopheryl acetate before slaughter as well as careful selection of the slaughtering method may greatly enhance the flesh quality of market-size turbot.