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This study assessed the use of different types of substrates for lumpfish in sea pens. Observations were recorded in the early morning before first light, and the number of lumpfish attached to each surface type was recorded. The substrate was removed and another design was deployed if no lumpfish were attached to a substrate for more than 2 weeks. Lumpfish preferred flat and smooth vertical surfaces of plastic, as very few preferred to attach to stones and car tyres offered. Some lumpfish were also observed attaching to the floating seaweed placed into the cages, a more natural substrate used in the wild. It is concluded that lumpfish will easily adhere to artificial, smooth, plastic surfaces instead of natural surfaces such as kelp. Irrespective of the type of substrate offered, it is critical to the welfare of the fish that they have access to some form of substrate due to the need to rest and attach overnight. [ABSTRACT FROM AUTHOR]

Juvenile Atlantic cod, Gadus morhua, that had been fed rotifers as larvae (R group) had significantly lower growth rates (SGR) at high-ambient ammonia (UIA = 115-120 μg l) than did juveniles that had been first fed with natural zooplankton (Z group). Overall specific growth rates (SGRs) were 5-11% higher in the Z group at the control ammonia (UIA = 1-2 μg l) treatments. An interaction between larval rearing history, oxygen and ammonia levels was found, as SGR decreased with decreasing oxygen levels at high ammonia in the R group, while the SGR in the Z group were less affected by hypoxia. At high-ambient ammonia, the SGRs were 5% (mild hyperoxia, 101-104% O in effluent water), 28% (normoxia, 83-88% O in effluent water) and 86% (hypoxia, 57-69% O in effluent water) higher in the Z group, compared to the R group. The present findings indicate that larval rearing environment could influence the adaptability to environmental changes and growth performance during later juvenile stage in cod. These findings have implications for the optimization of Atlantic cod culture. [ABSTRACT FROM AUTHOR]

To investigate the possible direct effect of a stepwise reduction in temperature with increasing size on growth, feeding parameters and muscle growth patterns of juvenile Atlantic halibut ( Hippoglossus hippoglossus L.), 804 juvenile halibut (mean initial weight individuals: 14.2 g ± 0.2 SEM) were reared at constant 9, 12 and 15°C or shifted (T-step, i.e. 15-12°C after 36 days) for 99 days. Despite indications of lower optimal temperature for growth with increasing size, equal end weights were obtained between the constant 12°C, constant 15°C and T-step groups. Best overall growth was observed for the group kept at constant 12°C. The limited effect of the T-step group may relate to the size at movement (too big), the temperatures investigated (close to optimum) and the time and size interval investigated (too narrow). Differences in growth were reflected more by alterations in feed intake ( C and F%) than by differences in feed conversion efficiencies (FCE). Differences were found with respect to the density of muscle cells, whereas no differences were found between the average muscle cell diameters. The mean diameter of muscle cells tended to increase only slightly with increasing fish weight, while the mean density of muscle cells tended to decrease. Using an optimum temperature of 12°C, an indication of a possible increased rate of hyperplasia in relation to higher growth was seen. [ABSTRACT FROM AUTHOR]

In order to test seasonal, rearing, maturing and anaerobic muscle activity effect on the flesh quality of turbot ( Scophthalmus maximus) a total of 80 farmed turbot from three different strains from reared under natural or continuous light were killed by a percussive blow to the head in November (winter, Icelandic strain), March (spring, Portuguese strain) and June (summer, domesticated strain (France turbot)). To test the effect of anaerobic muscle activity, 10 fish were on each occasion pre rigor filleted, where one fillet was used as a control, while the other fillet was electrically stimulated using a squared 5 Hz, 10 V pulsed DC for 3 min. All pre rigor fillets were measured for pH, weighed, wrapped in aluminum foil and stored in polystyrene boxes with ice. After 7 days of storage the fillets were measured instrumentally for pH, drip loss, colour (CIE L* a* b*) and texture properties such as hardness and shear force, while fillet shrinkage and colour (RBG) were evaluated with computer imaging on photographs from a standard lightbox. Results showed that softness of the flesh was mainly influenced by factors associated with growth, such as season, photoperiod and maturation. Anaerobic muscle activity simulated with electrical stimulation caused an increase in drip loss (<1%) and loss of shear force (<4%), but had no effect on hardness or fillet shrinkage. Computer imaging revealed that muscle contractions related to the electrical stimulus forced out blood from the fillet causing less reddishness for the entire storage period. We conclude that a pH drop upon slaughter associated with anaerobic muscle activity has a minor effect on the flesh quality in the short run, while seasonal/alternatively genetic effects are predominant. [ABSTRACT FROM AUTHOR]