Albert K. Imsland

The interaction of temperature and salinity on growth and food conversion in juvenile turbot (Scophthalmus maximus)

Abstract The effects of temperature and salinity on growth and feed conversion of juvenile turbot (initial mean weight 14 g) were investigated by rearing fish at (mean±SD) 10±0.2°C, 14±0.2°C, 18±0.3°C and 22±0.2°C and 15±0.4‰, 25±0.4‰ and 33.5±0.1‰ for 3 months. Growth, food consumption, and food conversion efficiency were highest at 15‰, and lowest at 33.5‰. There was an interactive effect of temperature and salinity at the two highest temperatures (18°C and 22°C) but not at 10°C and 14°C. The optimal temperature for growth (Topt. G) varied with salinity: Topt. G at 33.5‰ was 19.6±0.3°C (±SEM), whereas the Topt. G at 15‰ was 22.9±1.0°C, and at 25‰ was 24.7±2.1°C. A similar trend was found for food conversion efficiency (FCE). The optimal temperatures for FCE were 17.4±0.5°C, 17.9±1.0°C and 19.0±0.9°C at 33.5‰, 25‰ and 15‰, respectively. Overall, we found the optimal temperature–salinity combination for growth to be 21.8±0.9°C and 18.5±0.8‰. The optimal temperature–salinity combination for food conversion efficiency was found to be 18.3±0.6°C and 19.0±1.0‰. It is concluded that growth and food conversion efficiency of juvenile turbot can be improved by rearing them at intermediate salinities in the upper temperature range.

Growth, oxygen consumption and activity of juvenile turbot (scophthalmus maximus L.) reared under different temperatures and photoperiods

Abstract Juvenile turbot (5–125 g) were reared under two experimental temperatures: 10°C and 16°C, and three experimental photoperiods: LDN (natural photoperiod), LD 16:8 (16 h light: 8 h darkness), LD24:0 (continuous light), to study effects of temperature and photoperiod on growth, activity and oxygen consumption. Growth was strongly affected by temperature and was higher at 16°C than at 10°C. Continuous light had a growth-promoting effect at 10°C from mid-December to late March, while at 16°C this effect was restricted to December and January. A seasonal change in the condition index was found. The groups reared in continuous light had higher condition indices in winter. The experimental groups held at 16°C had higher O2 consumption than those at 10°C. The LD24:0 groups invariably had a higher overall O2 consumption than did the LDN and LD16:8 groups, the differences being caused by reduced O2 consumption in the latter groups during darkness. The LD24:0 groups displayed higher activity than the LDN groups, in which activity was very low at night.

The influence of temperature and ration on growth, feed conversion, body composition and nutrient retention of juvenile turbot (Scophthalmus maximus)

Abstract The influence of two water temperatures (16 and 22 °C) on growth, feed conversion, body composition and nutrient retention was investigated in juvenile turbot fed to satiation (0.9% and 1.1% bw day−1 at 16 and 22 °C, respectively) and at restricted rations of 65% and 35% of the satiation level at each temperature. Fish fed the same % rations at 16 and 22 °C did not differ in final mean weight or specific growth rate, which decreased at restricted rations. Feed restriction did not result in an increase in size heterogeneity over time at any temperature, as indicated by the stability of the coefficients of variation of weight (ΔCVw=1.00–1.13%). At both temperatures, the best feed conversion efficiency (FCE) was found at the 65% ration, and the FCE from fish fed the same rations was higher at 16 °C (1.30 g g−1) than at 22 °C (1.17 g g−1). A similar trend was found in energy and protein retention levels. At both temperatures, fish fed 35% rations had lower body lipid and higher ash and moisture content compared to fish fed to satiation, with the most pronounced effects on lipid (4.8% vs. 7.8% bw) and ash (4.1% vs. 3.6% bw) at 22 °C. Feeding ration proved to be the main differentiating factor in all growth, feed conversion and body composition parameters, whereas additional temperature and/or interaction effects were found in FCE, whole body protein, lipid, moisture and energy contents. Between fish fed 100% and 65% rations, only minor differences were found, but at 35% ration, the rearing temperature of 22 °C had a pronounced negative influence, and resulted in a reduction of available anabolic energy for growth and adaptive responses.

Gill Na + ,K + -ATPase activity, plasma chloride and osmolality in juvenile turbot (Scophthalmus maximus) reared at different temperatures and salinities

Abstract The interactive effects of temperature and salinity on gill Na + , K + -ATPase activity, plasma chloride and osmolality of juvenile turbot were investigated by rearing fish at (mean±S.D.) 10±0.2, 14±0.2, 18±0.3 and 22±0.2 °C and salinity of 15±0.4‰, 25±0.4‰ and 33.5±0.1‰ for 3 months. Gill Na + , K + -ATPase activity, plasma chloride and osmolality were lowest at 15‰, and highest at 33.5‰. Highest gill enzyme activity was at 22 °C, and overall, there was a positive correlation between temperature and Na + , K + -ATPase activity. Overall, we found the optimal temperature–salinity combinations corresponding to minimum Na + , K + -ATPase activity ( T & S min ATPase ), plasma chloride ( T & S min Cl ) and plasma osmolality ( T & S min Osm ) to be 17.6±2.2 °C–15.8±4.1‰, 15.1±0.5 °C–18.9±2.0‰ and 15.6±3.0 °C–13.6±3.2‰, respectively. Although slightly lower, these values correspond to published optimal temperature–salinity combination for growth of juvenile turbot suggesting some energy-saving effect on osmoregulation in groups reared at low (15‰) and moderate (25‰) salinities. We hypothesize that the reduced gill Na + , K + -ATPase found at intermediate salinities will lead to reduced energy expenditures thereby contributing to higher growth rates seen in previous studies. Our findings may have implications for turbot farming as production may be expanded into new areas, which have previously been regarded as unsuitable for culture of turbot due to low salinity.

Photoperiod regulation of growth of juvenile Atlantic halibut (Hippoglossus hippoglossus L.)

Abstract Juvenile Atlantic halibut ( Hippoglossus hippoglossus L., initial weight (SD) 31.1 g (±5.8 g)) were reared for 147 days at a constant temperature of 11°C and subjected to four different light regimes from February 10: continuous light (LD 24:0), simulated natural photoperiod of Bergen (60°25′N, LDN), constant 8 h light:16 h dark (LD 8:16) and LD 8:16 switched to continuous light on May 4 (LD 8:16–24:0). Fish exposed to LD 24:0 had a significantly higher specific growth rate (1.05% day −1 ) than those on LDN (0.98% day −1 ). Fish exposed to LD 8:16 had the poorest growth (0.80% day −1 ). The group on LD 8:16–24:0 (overall growth rate 0.94% day −1 ) grew poorly at first but subsequently increased growth rate after having been exposed to continuous light. This response was delayed by at least 21 days, suggesting that the fish needed some time to adapt to the change in photoperiod. Sensitivity to continuous light became less pronounced under summer photoperiods (above approximately 18 h daylength), which suggested that continuous light could be used to improve growth in juvenile halibut when the natural daylength is less than approximately 18 h. Overall mortality was 11.9%, with significantly higher mortality being observed in the LDN (17.4%) and LD 8:16–24:0 (17.1%) groups than in the LD 24:0 (6.2%) and LD 8:16 (6.8%) groups. Size-dependent mortality was seen in LD 8:16–24:0 in all periods from May 4 to July 6, with mortality being higher amongst small fish.

Effects of exposure to extended photoperiods during the first winter on long-term growth and age at first maturity in turbot (Scophthalmus maximus)

The effects of photoperiod on growth of juvenile turbot and the consequences of extended daylength on age at first maturation were investigated. Growth of individually tagged turbot (initial weight 34–44 g, n = 94) was monitored for 18 months. The fish were held under natural photoperiod from hatching (July) until the start of the experiment in December. From December 4, 1991 until May 26, 1992, the fish were reared under constant light (LD24:0, n = 27), 16-h light:8-h darkness (LD16:8, n = 35), or simulated natural photoperiod for 60 °25′N (LDN, n = 32). The fish were then reared together on LDN for 12 months until first maturation during summer 1993 (age 24 months). The fish were held at 16 °C from December 1991 onwards. A growth promoting effect of extended daylength was seen in the LD16:8 and LD24:0 groups, but the effect was not apparent in the LD24:0 group until 6 months after the fish had been transferred to LDN. The final mean weights of the female turbot were 1727 g and 1777 g in the LD16:8 and LD24:0 groups, respectively, whereas final mean weights of males in these groups were 1075 g and 1055 g. In the LDN group the final mean weights for females and males were 1290 g and 909 g, respectively. The results from the present study suggest that exposure to extended photoperiod alters the growth pattern of both maturing fish and immature fish resulting in increased overall growth. Fewer males matured in the LD16:8 (26%) and LD24:0 (17%) groups than in the LDN (56%) group, whereas there were no differences between the experimental groups in the proportion of females that matured (range = 60–63%). It is concluded that extended daylength

Effects of size grading on growth and survival of juvenile turbot at two temperatures

Juvenile turbot were size graded into three size groups (mean initial size): Small (3.4 g), medium (7.0 g) and large (10.5 g), and additional fish were held in ungraded (6.6 g) groups. Subgroups (n = 396) of fish were tagged and individual growth rates and social interactions within different size categories were studied in fish reared at 13 and 19 °C. Size grading of juvenile turbot did not improve growth. Specific growth rates (SGR) were mainly size-related, and no differences in SGR or mortality between the experimental groups at both tem-peratures were found. A higher level of social interactions was indicated amongst medium-sized fish than amongst those in the smallest and largest categories. Excess feeding may have been important factors in reducing aggression, so that the growth of the smallest individuals was not suppressed by the larger individuals in the present study. Grading seems to be an unnecessary operation to improve the growth and survival of juvenile turbot (5- 150 g). However, as it was mainly the smallest individuals in each group that died, grading of very small turbot (2-5 g) can be recommended.

Size dependent variation in optimum growth temperature of red abalone (Haliotis rufescens)

Six size groups of red abalone Haliotis rufescens (geometric mean shell lengths: 21, 25, 33, 66, 81 and 98 mm) were reared on a macroalgal diet for 4 months at seven different temperatures between 11 and 22 jC. The results demonstrate that red abalone exhibit size dependent variation in growth potential and temperature optimum for growth. The maximum growth rate was found to have a skewed, third degree polynomial relationship with shell length, reaching a maximum of 111 Am day � 1 at 38 mm shell length. The temperature optimum for growth was found to have a symmetrical, concave relationship with shell length from 16 mm to maturity, reaching a peak of 17.8 j Ca t 44 mm shell length. The minimum grow-out time from spat to market size on an optimum temperature regime was predicted less than 2 years. The results from the present study could contribute to an increase in the potential yield from landbased abalone farming. D 2003 Elsevier Science B.V. All rights reserved.

Effect of Electric Field Strength and Current Duration on Stunning and Injuries in Market-Sized Atlantic Salmon Held in Seawater

Abstract We evaluated electricity as a stunning method before slaughter of Atlantic salmon Salmo salar by assessing both stunning effectiveness and injuries. About 300 salmon (1.2–6.6 kg) were exposed to one-phase, sinusoidal, 50-Hz AC in seawater; electrical field strengths ranged from 15 to 250 V/m and current durations from 0.2 to 12 s. We measured the duration of the epileptic-like seizures after stunning and the degree of unconsciousness based on behavioral responses. Fish were killed, bled, and gutted 10 min after stunning and then analyzed for injuries. The proportion of fish sufficiently stunned, the duration of an unconscious condition, and the occurrence of broken vertebrae and hemorrhages were all dependent on electric field strength and current duration. The electric field strength required to stun the fish was inversely proportional to the current duration, dropping from 200 V/m at 0.8 s to 25 V/m at 6–12 s. Electricity proved to be efficient in stunning fish, but to avoid injuries in market-...

Genetic heterogeneity and growth properties of different genotypes of Atlantic cod (Gadus morhua L.) at two spawning sites off south Iceland

Abstract To investigate possible differences in life history traits of Atlantic cod in Icelandic waters, cod were collected at two spawning areas off Southwest Iceland (Loftstaðahraun and Kantur) in two surveys during the spawning season. The sampled fish were measured and age and sex determined. In addition they were analysed for allelic variation at the synaptophysin ( Syp I) locus. Significant differences in growth performance and Syp I genotype distributions were found between the sampling localities. The cod sampled at Loftstaðahraun displayed higher mean weight and length compared to the cod from Kantur and this was mainly related to higher age. Significant differences in genotype ( Syp I) were also observed between cod collected at the two sampling sites. The results indicate that the cod spawning in south Icelandic waters do not belong to one panmictic population and these populations seem to display different life histories.