Atle Foss

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.

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.

A review of the culture potential of spotted wolffish Anarhichas minor Olafsen

The first articially fertilized spotted wolffish eggs hatched only 10 years ago, and today the species is considered a very promising candidate species for cold water aquaculture in the North Atlantic. Recent research has focused on identifying key biological parameters in spotted wolffish aquaculture in order to establish a full production line for the species, and basic aspects of reproduction and larval development are now understood, controlled, and no longer limiting production. Spotted wolffish eggs (5–6 mm) have a protracted incubation period (800–1000 D°) and newly hatched individuals (20–25 mm) are well developed, with the only larval characteristic remaining being a relatively small yolk sac which is completely resorbed after 3–4 weeks. The species can be weaned directly on formulated feed, and high specific growth rates have been obtained in land-based culture facilities using shallow raceways. Adaptive immune responses are present early after hatching and few potential disease problems have been identified. Only one bacterial disease, atypical furunculosis, has been reported in farmed fish, but oil-emulsified vaccines have displayed efficient protection both in juvenile and adult fish. Ectoparasites may, however, constitute a problem during parts of the year when sea-water temperature increases.Optimal temperature for growth decreases with increasing fish size and is 10–12 °C for early juveniles and 4–6 °C for adult fish and broodstock. Spotted wolffish is a very robust species, and juveniles thrive at high densities and may be reared at a wide range of salinity levels. The species has further displayed a high tolerance to environmental changes in water quality parameters such as oxygen, carbon dioxide and un-ionized ammonia. Currently, the possibility of rearing spotted wolffish in flat-bottom net cages with shelves in the sea is being investigated. Preliminary results suggest that sea-based production may be a viable alternative to land-based rearing of the species in certain areas.

The influence of first-feeding diet on the Atlantic cod Gadus morhua phenotype: survival, development and long-term consequences for growth

Atlantic cod Gadus morhua larvae reached four-fold (at low larval density) to 11 fold higher body mass (high larval density) at 50 days post hatch (dph) when fed zooplankton rather than enriched rotifers. A short period (22-36 dph) of dietary change affected larval growth positively if changed from enriched rotifers to natural zooplankton and negatively if prey type changed vice versa. Overall survival did not differ between the two larval groups at low larval density, but at high density the rotifer group had a higher overall survival (10.8% v. 8.9%). Long-term growth was affected significantly by larval diet in favour of the zooplankton diet; juveniles reached a 23% higher mass in a 12 week growth period. No difference in growth performance was found between juveniles fed natural zooplankton during the larval period for 36, 22 or 14 days, but all these juveniles performed significantly better compared with the rotifer-fed group. These findings suggest that optimal diet during a short period in the larval period can result in improved growth in both the larval and juvenile period. Improved rotifer quality may, therefore, hold a large potential for growth improvement in this species.

Environment affects stress in exercised turbot

We investigated the interaction of water temperature (10, 18 and 22 degrees C) and salinity (33.5 and 15 per thousand ) on the stress response of juvenile turbot. At each temperature/salinity combination, fish were subjected to 10 min enforced exercise. This induced a moderate stress response, which differed at the various temperature and salinity combinations. High temperatures caused more rapid increases in plasma cortisol and glucose, larger and more rapid increases in plasma lactate levels, which were also influenced by body weight, and a faster recovery in plasma Na(+) and Cl(-). Low salinity ameliorated cortisol responses at low but not at high temperatures. The magnitude of ionic disturbance was reduced at 15 per thousand. Plasma K(+) did not change at any temperature or salinity. The stress response involved activation of the brain-pituitary-interrenal axis, as indicated by the cortisol elevations. The low magnitude of glucose responses, the mild Na(+) and Cl(-) disturbances, and the lacking K(+)-responses indicated mild activation of the brain-sympathetic-chromaffin cell axis, and hence a low release of catecholamines, which seemed though to occur to a higher extent at higher temperatures. The relatively low catecholaminergic response of turbot may be linked to their inactive sedentary lifestyle. The higher responsiveness at higher water temperatures may reflect a higher overall adaptive capacity.

Variations in growth in haemoglobin genotypes of Atlantic cod

In the present paper are described the growth properties of three different haemoglobin genotypes of juvenile Atlantic cod (Gadus morhua) reared at 7, 10, 13 and 16 °C. In addition one group was reared under “temperature steps” i.e. moved successively from 16 to 13 and 10 °C. The genotype Hb-I(2/2)displayed the overall highest growth rate in the temperature range 13–16 °C, whereas the Hb- I(1/1)genotype showed the highest overall growth at the lowest temperature (7 °C). Accordingly, we found a significant interaction between genotype and temperature. The differences in growth were largest when cod were reared under the temperature step regime where the Hb-I(2/2)genotype displayed 17 and 24% higher growth than Hb-I(1/1)and Hb-I(1/2),respectively. Optimal temperature for growth (Topt.G) varied between the genotypes with the genotype Hb-I(1/2)displaying the highest (mean ± SE) Topt.G (14.5 ± 1:0.8 °C) and Hb-I(1/1)the lowest (12.5 ± 0.2 °C). The biological significance of this link between biochemical genetic variation and physiological properties might be the influences on growth pattern, ultimate size and age at first maturity.

Notes on the behaviour of lumpfish in sea pens with and without Atlantic salmon present

Abstract The behaviour of lumpfish, Cyclopterus lumpus L., in sea pens, with and without Atlantic salmon, Salmo salar L., present, was assessed by underwater camera technology. Behaviour was classified by recording the principal activity of individual fish for 30-s intervals. The majority of daylight time was spent actively foraging for food. Antagonistic behaviour between Atlantic salmon and lumpfish was not observed during the whole experimental period and no mortality was seen in either species. Cleaning behaviour, but at low frequency, was observed as lumpfish cleaned sea lice off Atlantic salmon. Significantly lower sea lice infection levels were seen on Atlantic salmon when reared together with lumpfish compared to the control group without lumpfish. Feeding behaviour can be classified as strongly opportunistic.

Selection or adaptation: Differences in growth performance of juvenile turbot (Scophthalmus maximus Rafinesque) from two close-by localities off Norway

Abstract Growth perfonnance was investigated in two populations of juvenile turbot (Scophthalmus maximus Rafinesque) from two close-by localities on the Norwegian coast, both caught at the southwest coast and called SW1 and SW2, reared together under four different temperature regimes. All growth indices showed that the growth performance of the SW1 Norwegian population was superior compared to the SW2 Norwegian population especially at the extreme temperatures. Our findings may indicate local adaptation of turbot. We discuss if local adaptation will be reflected in neutral genetic markers as the variation in growth is higher than the genetic variability previously reported for this species, which might make the non-neutral markers a better tool to understand local adaptation of fish populations. Alternatively our results could indicate hatchery selection or a strong genetic drift which may cause a substantial genetic change eventually leading to inbreeding depression which again may cause decreased growth.

Plasma insulin-like growth factor-I concentrations and growth in juvenile halibut (Hippoglossus hippoglossus): Effects of photoperiods and feeding regimes

The effects of photoperiod and feeding regimes on plasma IGF-I levels and their relationship with growth rate of juvenile halibut (initial mean weight 364 g) were investigated by rearing fish under five different photoperiod regimes and two feeding regimes for 14 months. The entire photoperiod experiment was divided into 3 phases where the fish in each phase were exposed to either natural photoperiod (N), stimulated photoperiod with long day and short night (S) or continuous light (L). Thus, the following five photoperiod combinations were tested: a) Control group (NNN) b) Group 2A (NLN) c) Group 2B (NNL) d) Long day-natural group (SNN) e) Production group (LNN). In addition, the Control group was split into two parts and fed according to two different feeding regimes: a) Continuous fed group: Fish fed every day. b) Starvation/re-fed group: Fish were starved for 5 weeks and then re-fed for 10 weeks, and the treatment repeated during the whole experimental period. The analyses of IGF-I were performed from individually tagged fish in all groups in September 2005 and March 2006. In order to test how rapidly starvation affects circulating IGF-I levels samples were taken from the Starvation/re-fed group after a 10 days starvation (September) and immediately after 10 weeks of feeding (March). A significant relationship between IGF-I levels and individual growth in the preceding period and photoperiod and starvation treatment was found on both occasions. In conclusion, the present study indicates that plasma IGF-I levels are correlated to growth in Atlantic halibut, and affected by photoperiod treatment or compensatory growth during re-feeding. Correlation between individual growth rate and IGF-I levels was low, but significant, highlighting the complexity of how environmental factors affect the endocrine and physiological regulation of growth in fish.

Ontogenetic effects of diet during early development on growth performance, myosin mRNA expression and metabolic enzyme activity in Atlantic cod juveniles reared at different salinities.

This study investigates the effect of diet during early development on growth and metabolic capacity in the juvenile stage of Atlantic cod. Growth in three groups of Atlantic cod juveniles (10-70 g) was measured at two salinities (15 per thousand or 32 per thousand) in combination with two temperatures (10 degrees C or 14 degrees C). Groups of cod from a single egg batch differed by having been fed with rotifers (R) or natural zooplankton (Z) during the first 36 days post hatch. A third group was fed zooplankton from 1 to 22 dph, after which diet changed to rotifers from 22 to 36 dph (ZRZ). All fish were weaned at 36 dph. Juveniles from the Z and ZRZ groups performed equally well under all experimental conditions, but fish that had received rotifers as a larval diet showed overall significantly lower growth rates. Growth was significantly enhanced by reduced salinity. Metabolic enzyme activity and relative myosin mRNA expression levels were not affected by larval diet. Muscle AAT and MDH were affected by salinity while these enzymes in liver tissue were affected by the interaction between salinity and temperature. Metabolic enzymes were stronger correlated with fish size than growth rates. Our results indicate that larval diet has a pronounced effect on juvenile growth rates under varying environmental conditions as optimal larval diet (zooplankton) increased juvenile growth rates significantly. Metabolic enzyme activity and relative myosin mRNA expression were not affected by larval history, which suggests that the persisting juvenile growth difference is not a result of differing metabolic capacity.