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Tetraploid fish are the key source of diploid gametes in polyploid breeding, and they can be induced by disrupting the first mitotic cell cleavage. In this study, the induction protocol of tetraploid by hydrostatic pressure shock and the viability of the tetraploid progenies were investigated in turbot, Scophthalmus maximus. Under water temperature of 14.5 ± 0.5 °C, fertilized diploid zygotes were treated by different combination of timing (65–90 min after fertilization, maf), pressure intensity (60–85 MPa), and duration (2–10 min), respectively. Ploidy level was determined by silver staining of NOR regions, karyotype analysis, and flow cytometry. The optimal protocol for the pressure shock induction was determined to be the combination of timing of 80 maf, 75 MPa of hydrostatic pressure, and 6 min of duration time. Two batches of tetraploid-induced progenies with a total of more than 73,000 morphologically normal larvae were produced. The hatching rates and tetraploidy rates of the two induction groups were 8.97% and 4.09% and 53.33% and 46.67% at 1 day after hatching (dah), respectively. At 150 dah, 1 out of 20 juveniles was identified as tetraploid by karyotype analysis. However, none of tetraploid juveniles was detected by the flow cytometry analysis among the 446 juveniles survived at 365 dah. This preliminary study provides the evidence supporting the large-scale production of tetraploid turbot progenies, thus encouraging further research on the subject.

In this study, the concentration/activity of the immune components in the turbot (Scophthalmus maximus) seminal plasma at four time points with the intervals of 2 weeks has been summarized. The results showed that the concentrations of transferrin (TF), transforming growth factor-βs (TGF-βs), complement 3 (C3), IgM and interferon-1β (IL-1β) varied as experiment went on; it was the same with the activities of protease, lactate dehydrogenase and lysozyme. The correlation analysis showed that C3 and IgM were most positively related to motility and straight-line velocity (VSL)/curvilinear velocity (VCL), whereas protease was most negatively correlated with motility and VSL/VCL. This study highlighted the importance in the necessity and possibility in improving the sperm quality during the actual production.

This experiment was conducted to investigate the growth performance, stress and immune responses, and welfare of juvenile turbot (Scophthalmus maximus) under three different densities (initial density 9.3, 13.6, and 19.1 kg m−2) for 120 days in a recirculating aquaculture system. Turbot were measured every 20 days to evaluate growth biometrically and sampled every month to measure biochemical parameters and mRNA levels of some stress-related genes. No significant differences were detected in the parameters and gene expression among density groups until the final sampling, except Fulton’s condition factor, lysozyme, immunoglobulin M, and complement C3. At the end of the experiment (final density 26.11, 38.22, and 52.25 kg m−2), turbot reared in the high-density (HD) group had lower body mass increase, specific growth rate, and Fulton’s condition factor, as well as higher feed conversion ratio and coefficient of variation for weight than those reared in the low-density (LD) group (P

To investigate the effects of a mixture of hydrolyzed soybean and cottonseed meals (HSC) on the digestion, metabolic enzymes, growth-related hormones, and growth of turbot (Scophthalmus maximus) (initial weight ca 35 g), six isoenergetic (ca 20 kJ/g) and isoproteic (ca 45%) diets were formulated with 0 (control), 14.7% (HSC14.7), 29.4% (HSC29.4), 44.1% (HSC44.1), 58.8% (HSC58.8) HSC, and 44.1% its native protein (SC44.1). Each diet was assigned to triplicate tanks with 36 fish per tank in a re-circulating system. Fish were fed twice daily. After 54 days, fish were weighed after a 24-h fast, and five digestive tracts were dissected for digestive enzyme analysis. Six blood and liver samples were collected from remaining 31 fish at 5 h post-feeding for metabolic enzymes and hormones analysis. The results showed that fish fed diets containing 14.7–44.1% HSC had higher average weight gain (g) (38.77–41.52 vs 29.74) but lower feed conversion rate (0.83–0.88 vs 1.02) than fish given the control diet. The HSC diets increased apparent digestibility coefficients of dry material, protein, and energy from 73.82% to 80.03%, 87.38% to 93.68%, and 76.13% to 81.46%, respectively. Pepsin and trypsin activities (U mg prot−1) were higher in group HSC14.7 (4.94 vs 4.26, 141.66 vs 115.14) than in the control group. The HSC44.1 and HSC58.8 diets increased the serum insulin level (IU L−1) (5.38, 5.50 vs 4.05), as well as the activities (U g prot−1) of hepatic alanine transaminase (868.42, 938.71 vs 730.82), aspartate transaminase (793.84, 854.64 vs 600.30), and glucokinase (104.76, 109.17 vs 93.90). The HSC diets reduced glucose 6 phosphatase activity (262.27–383.81 vs 537.21, U g prot−1) but increased phosphofructokinase activity (1592.55–1983.71 vs 978.52, U g prot−1). The HSC29.4 diet increased insulin-like growth factor 1 level (187.30 vs 151.17, ng L−1). Fish fed the SC41.1 diet exhibited lower growth performance and diet utilization than those fed the HSC44.1 diet. In conclusion, juvenile turbot can efficiently utilize HSC, and the recommended inclusion level is 27.14–30.70%.

Feeding in larval fish is influenced by a range of factors and among these are the morphological and behavioral characteristics of their prey. We investigated the influence of the swimming behavior of two species of calanoid copepods, Acartia tonsa and Temora longicornis, on larval turbot feeding. The nauplii of these species represent two contrasting swimming behaviors: A. tonsa is a jump-sink type swimmer, while T. longicornis is a cruise swimming type. Three replicates of ten larvae aged 7 and 9 days post hatch (DPH) were observed feeding on one of the two copepod species using a 2-dimensional video setup. The results showed that the duration of aiming postures by turbot larvae was 2.3 times higher when turbot larvae approached T. longicornis as compared to A. tonsa nauplii, indicating that larvae can more easily position themselves, preparing for attack, when the prey is of the jump-sink type. The attack speed of turbot larvae feeding on A. tonsa nauplii decreased slightly from DPH 7 to DPH 9, whereas it increased when attacking T. longicornis nauplii. Capture success rate by turbot larvae feeding on A. tonsa was 58% and slightly higher, but not significantly different to capture success rate when feeding on T. longicornis (54%). We conclude that the differences between behavior and other characteristics of these prey species have only minor effect on larval fish feeding, suggesting that copepods species for live feed should be selected according to their ease to culture more than to their species-specific characteristics.

It is well established in Denmark to rear calanoid copepods in outdoor tanks for use as live feed during turbot (Scophthalmus maximus) larval production. However, the copepod assemblages, composed of a mixture of all development stages and therefore body sizes, vary over time and do not always match the larval needs. When turbot larvae reach metamorphosis and are transferred indoor for weaning, the outdoor tank sediments may reveal vast amounts of copepod eggs undergoing dormancy. Here, we report a copepod species succession firstly among Centropages hamatus and then Acartia spp. both with resting eggs as part of their life cycles as a result of two different nutrients treatments and a control. We found a tendency to a higher egg production and indeed more eggs in the sediment of nutrient amended tanks. In fact close to 5 million eggs per square meter, making up to 400 million eggs per tank was found in the sediment after one production. Instead of discarding the sediment between production batches, we propose to collect it and generate an egg bank. These eggs can be stored for months to a year, however, according to the results, a large loss rate occurred, which could be potentially decreased by the optimization of storage conditions. Those procedures will enable hatchery managers to apply newly hatched copepod nauplii exactly when the turbot larvae start feeding which would potentially solve the, often occurring, mismatch between the time of start-feeding turbot larvae and actual available prey field.

This study was undertaken to determine the effects of dietary lipid levels on growth and nutrient utilization, and carbon (C), nitrogen (N) and phosphorus (P) balances in juvenile turbot (Psetta maxima) in brackish water. Four isonitrogenous diets (50 % protein) differing in dietary lipid levels from 10 to 19 by 3 % increments (named 10L, 13L, 16L and 19L, respectively) were fed to four replicate groups of fish with an initial weight of 54.4 ± 0.2 g for 9 weeks. Significantly better growth and feed conversion ratio were observed in fish fed 13L than those fed 16L and 19L. The whole body, fillet, viscera and liver dry matter and lipid levels were increased as dietary lipid was increased. Liver protein levels were lower in 16L and 19L than 10L. There was an ascending pattern in the whole-body C levels and C/N ratios with the increase in dietary lipids. No significant effect of dietary lipids on either protein efficiency ratio or N and P retentions was detected. Dietary lipids led to an increase in C losses to the environment. Overall, high dietary lipids when introduced at an adequate protein level did reduce growth and feed utilization without a protein-sparing effect and resulted in higher C losses in juvenile turbot reared, and a dietary lipid level of about 13 % seemed to be optimum.

The aim of the study was to investigate the effects of the diets that contain safflower oil and fish oil as lipid sources, on growth, feed conversion and body composition in turbot (Psetta maxima). Two iso-nitrogenous and iso-lipidic diets (55 % protein and 14 % lipid) were prepared that include 100 % fish oil (FO group) and 100 % safflower oil (SFO group) for turbots with average weight of 62.21 ± 1.28 g, and fish were fed with these diets for 104 days. At the end of the experiment, the weight gain, specific growth rate and feed conversion ratio were the highest in SFO group than in FO group (p < 0.05). Fatty acid composition of fish body reflected the fatty acid composition determined in the experimental diets. The amounts of palmitic acid (PA; C16:0), oleic acid (OA; C18:1n-9), linoleic acid (LA; C18:2n-6) and docosahexaenoic acid (DHA; C22:6n-3) were dominant fatty acids in fish body. It was confirmed that the usage of safflower oil instead of fish oil in turbot feed did not generate any negative effects on growth, feed conversion and the values regarding the growth performance.

Bacterial diseases are probably the major cause of mortality in aquaculture. The use of probiotics is one of the solutions to manage bacterial infections, by preventing the colonization and exclusion of pathogenic bacteria. The effect of two selected probiotics in turbot (Psetta maxima) larvae was evaluated. Turbot larvae were reared on three different dietary treatments consisting of newly hatched Artemia nauplii from day 16 to 34 post-hatch. Groups A and B were fed with Artemia-containing probiotics FAA and FAB, respectively, and group C was control group. Results indicated that the addition of probiotics increased survival and promoted turbot growth, showing that they were beneficial for the aquaculture of turbot. Moreover, turbot fed with bioencapsulated probiotics attained higher percentages of survival during its development.

Probiotics are a live microbial feed supplement that beneficially affects the host animal. As aquaculture is one of the main areas where probiotics can be applied, the environmental suitability of using probiotics in hatching and nursing facilities for turbot farming was evaluated through the life cycle assessment (LCA) methodology. This LCA study showed that the potential environmental impacts associated with probiotic production are generally offset by the impact reductions linked to lower consumption levels and reduced waste and emission generation rates within the hatching and nursing subsystem. Thus, the use of probiotics is recommended in order to enhance the performance of turbot aquaculture systems provided that operational and economic advantages are attained.

The growth data of a commercial aquaculture recirculation system were analysed to investigate the growth performance of reared turbot (Psetta maxima). Three common growth models (von Bertalanffy, Gompertz and Schnute) were fitted to the growth data documented over a time period of 6 years. To determine the most suitable model, three different criteria were used: (1) the Akaike index criterion, (2) the sum of squared residuals and (3) the average daily deviation between the estimated final weight and the observed final weight. The evaluation of the growth models showed that the Schnute model had the lowest Akaike index, the lowest sum of squared residuals and the lowest daily deviation between estimated and real weight of all tested growth models. The Schnute model produced sigmoid growth curves. The estimated growth coefficients were the most realistic ones in regard to biological interpretation. In contrast, the von Bertalanffy growth model and the Gompertz model estimated inaccurate exponential growth curves and are therefore unable to simulate the growth data as well as the Schnute model. The results indicate that the von Bertalanffy growth model is not the optimal model to simulate the present growth data and that the growth potential of reared turbot has probably not yet been fully exploited in the aquaculture system(s) examined (so far).

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 (

Rotifer growth performance and microbial community changes associated with rotifer cultures were monitored while different feed types (Nannochloropsis oculata paste and the commercial yeast based feed CS-3000), different regimes (daily changes, changes per batch and no changes) and mixtures of three probionts (Phenylobacterium sp.; Gluconobacter sp. and Paracoccus denitrificans) were provided. It was shown that the dominant bacterial species in the cultures receiving either N. oculata or CS-3000 were different. However, in cultures receiving both feeds (either switching between feeds on a daily basis or on a batch basis), a high similarity in microbial community fingerprint was found. The presence of probionts was detected by the end of four batch culture cycles in spite of strong shifts of the bacterial community. By group discriminant analysis, it was found that Phenylobacterium sp. and Paracoccus sp. contributed positively to the CS-3000-fed group, while Gluconobacter sp. contributed positively to the N. oculata-fed group, although they did not appear as very dominant species.

The wedge sole is a target species in the fisheries of the Gulf of Cadiz (Spain). Having reared them to commercial size, we have studied reproduction and breeding in captivity of the wedge sole in this work here. The breeders adapt easily to captivity, and they can spawn in less than 1 year in captivity. The relative fecundity is relatively high, 1.06–2.33 · 106 eggs kg−1 per spawning season (mean 1.6 ± 0.1). Larval SGR is high, 7.2 ± 0.2% day−1 (range 5.8–9.1), similar to other cultured flatfish species. In 1 year, some individuals reach market size and can release eggs, registering SGRs of 1.39–1.66% day−1 (mean 1.56 ± 0.01). This species presents some very different characteristics with respect to other farmed flatfishes (turbot, halibut and Senegal sole, mainly), so that it is necessary to develop new techniques to optimise its cultivation. In the present work, the first results are presented on the biology of the wedge sole in captivity.

The effect of thermal history (16 and 20°C) on growth of juvenile turbot, Scophthalmus maximus (initial mean weight 72.6 g, n = 157) was studied. Fish were divided into four groups, two groups remaining at constant temperature (C16, C20), while fish in the other groups were transferred from either 16 to 20°C (F16-20) or from 20 to 16°C (F20-16). Between 35 and 42 fish in each tank were individually tagged at the start of the experiment. The final mean weights were significantly higher in the F20-16 group (230 g) than in the C20 (213 g), F16-20 (211 g) and C16 (205 g) groups. The overall growth rate was highest in the F20-16 group (1.17% day¿1) but comparable in the three other groups (1.00¿1.04% day¿1). Our findings indicate that, even at near-optimal temperature for a given size, the temperature history of the fish may influence future growth. Based on these indications, we conclude that as turbot grow larger, the temperature should be reduced to take advantage of the change in optimal temperature for growth with increasing fish size rather than rearing at constant temperatures.

The effect of extended photoperiods on growth and age at first maturity was investigated in 166 (79 females and 87 males) individually tagged Atlantic halibut Hippoglossus hippoglossus and in 114 (50 females and 64 males) individually tagged turbot Scophthalmus maximus. The halibut were reared at 11 °C on four different light regimes from 10 February to 6 July 1996: simulated natural photoperiod, (LDN), continuous light (LD24:0), constant 8 h light and 16 h darkness (LD8:16) and LD8:16 switched to continuous light 4 May 1996 (LD8:16–24:0). From 6 July 1996 to 9 February 1998 the LD24:0 and LD8:16–24:0 were reared together under continuous light and the LDN and LD8:16 together under natural photoperiod. The turbot were reared at 16 °C on three different light regimes: constant light (LD24:0), 16 h light:8 h darkness (LD16:8), or simulated natural photoperiod (LDN). After 6 months on the different photoperiods, the turbot was reared together on LDN for approximately 12 months until first maturation. Juveniles subjected to continuous light (halibut) or extended photoperiods (halibut and turbot) exhibited faster growth than those experiencing a natural photoperiod or a constant short day. Moreover, when the photoperiod increased naturally with day-length or when fish were abruptly switched from being reared on short-day conditions to continuous light, a subsequent increase in growth rate was observed. This growth enhancing effect of extended photoperiods was more apparent on a short time scale in Atlantic halibut than in turbot, but both species show significant long-term effects of extended photoperiods in the form of enhanced growth. In both species lower maturation of males was seen in groups exposed to extended or continuous light compared to LDN and this could be used to reduce precocious maturation in males leading to overall increase in somatic growth.

The aim of the study was to compare theantioxidant systems in juvenile marine fish ofcommercial importance to European aquaculture,namely turbot (Scophthalmus maximus),halibut (Hippoglossus hippoglossus) andgilthead sea bream (Sparus aurata). Thepresent dietary trial was specifically designedto investigate the antioxidant effects ofvitamin E under moderate oxidising conditions,including high dietary levels of highlyunsaturated fatty acids and the feeding ofoxidised oils. The objective was to induce astressful pro-oxidant status to enablecharacterisation of the biochemical responsesto peroxidative stress without causingunnecessary suffering to the experimentalanimals or high mortalities during the trials. Both sea bream and turbot showed excellentgrowth, whereas growth was poorer in halibut.Dietary oxidised oil significantly reducedgrowth in turbot and especially in halibut, butnot in sea bream. Vitamin E improved growth insea bream fed oxidised oil but not in turbot orhalibut. However, vitamin E supplementationappeared to improve survival in all threespecies. In sea bream and turbot, liverantioxidant defence enzyme activities weregenerally increased by feeding peroxidised oiland reduced by vitamin E. Conversely, inhalibut, the liver antioxidant defence enzymeactivities were not increased by feedingperoxidised oil and only superoxide dismutasewas reduced by feeding vitamin E. Consistentwith these data, feeding oxidised oil increasedlipid peroxidation products in halibut, butgenerally not in sea bream or turbot.Furthermore, lipid peroxidation products weregenerally reduced by dietary vitamin E in bothsea bream and turbot, but not in halibut. Therefore, halibut liver antioxidant defenceenzymes did not respond to dietary oxidised oilor vitamin E as occurred in turbot and,especially sea bream. This resulted inincreased levels of lipid peroxides in halibutcompared to turbot and sea bream in fish givendietary oxidised oil. In addition, supplementalvitamin E did not reduce lipid peroxides inhalibut as it did in turbot and sea bream. Theincreased peroxidation stress in halibut mayaccount for their poorer growth and survival incomparison to turbot and especially sea bream.Halibut were reared at a lower temperature,although relatively high for halibut, thaneither turbot or sea bream but they were alsoslightly younger/smaller fish and possibly,therefore, more developmentally immature, andeither or all of these factors may be importantin the lack of response of the liver enzymes inhalibut.

The development of neutral lipase and phospholipase activities was studied in larval turbot fed live prey. Activities of neutral lipase and phospholipase (activity larva−1) increased significantly between days 6 and 24 after hatching in turbot larvae. The specific activities of both enzymes (activity µg protein−1) decreased in older larvae. Feeding of a microdiet for 3 days (days 10–13) affected the lipolytic activity of neutral lipase and phospholipase negatively, compared to the larvae fed on rotifers. Since neutral lipase activities in whole larval homogenates and in the gut were significantly lower, it suggests a reduced synthesis rate and a reduced secretion of the enzyme in larvae fed the microdiet. A correlation between neutral lipase and phospholipase activities was found in larvae fed rotifers, but not in larvae fed the microdiet. This may indicate different regulating and stimulating mechanisms for these enzymes. The contribution of exogenous enzymes from ingested live prey to the total larval enzyme activity was about 6% for neutral lipase and 10% for phospholipase on day 6. The exogenous prey enzymes accounted for only 2% of the total activities in 12-day-old turbot larvae, suggesting that enzymes from prey did not contribute considerably to the digestion of lipids.

Turbot and Atlantic halibut are highly valued fish species. However,very little is known about fillet shelf-life characteristics associated withboth species. Thus, fillet α-tocopherol content and proximate compositionof wild turbot (1.5 kg) and Atlantic halibut (1.1 kg)caught off the south coast of Ireland and the north-west coast of Iceland,respectively, were investigated. In addition, the susceptibility of fillets, storedunder retail conditions, to lipid oxidation and colour change was studied.Proximate composition analysis showed that turbot had significantly highermoisture (P < 0.001) and lower protein (P < 0.001) contents compared toAtlantic halibut. Atlantic halibut incorporated significantly higher (P

The effect of 18 mg. melatonin (MLT) implants on thereproductive performance of turbot (Scophthalmus maximusL.) broodstock was determined in 20 females and 12 males. Implantedanimals showed supra-physiological plasma MLT concentrations during threemonthsafter implantation, being at that time about one hundred times higher thandiurnal MLT concentrations. Direct effects of MLT implants were observed ongonadal maturation of turbot females three months after implantation (P

Two bacterial strains, 4:44 and PB52, isolated from turbot(Scophthalmus maximus L.) were used during a first feedingexperiment with turbot larvae. Bacteria were either added directly tothe water on the day of hatching of the larvae (day 0), orbioencapsulated in rotifers (Brachionus plicatilis) distributedon day 2 after hatching. The two bacterial strains were found to bepresent in the water of the rearing tanks throughout the experiment. Theaddition of bacteria influenced the species-composition of themicroflora associated with intensively produced rotifers added to thetanks, and resulted in colonization of the gut of the larvae by theadded bacterial strains. The strain 4:44 showed a peak on day 9 afterhatching, and reached a mean(sem) of 2.5(1.4) × 104bacteria per larva, when added in a mixture with PB52, and 0.4(0.1)× 104 bacteria per larva, when added alone. The strainPB52, on day 12 after hatching, reached 5.2(1.5) × 104bacteria per larva when added in a mixture with strain 4:44, and12.5(0.7) × 104 bacteria per larva, when added alone.The added bacteria colonized the gut turbot larvae, whereas thebacterial land, the survival and growth of the larvae were in most casesnot influenced in a negative way by the addition of bacteria.

Varying egg quality is one of the main factors interfering with the reliable performance of marine fish hatcheries. As larval performance during the first period largely depends on the availability of essential nutrients, the endogenous provision of these nutrients through the egg stages, and possibly parental diet, might be an important tool in improving hatchery output. Therefore, several feeding experiments were conducted on turbot (Scophthalmus maximus) broodstock reared under production conditions at two commercial facilities in France: France Turbot (FT) and Sepia Conseil (SC). Diets varied mainly in essential fatty acids (ω-3 HUFA), Vitamins C and E, and were fed for 2–3 months prior to the reproductive season. Egg quality parameters, i.e. fertilization and hatching rate, egg and oil droplet diameter, and biochemical composition, were monitored for each female during its total reproductive phase. Egg size during the reproductive cycle showed a low variability among females receiving the same treatment, but became significantly smaller as the season progressed. The same occurred for the oil globule in the non-vitamin supplemented groups, whereas it significantly increased in the vitamin-supplemented groups. However, these observations could not be correlated with any of the hatching or fertilization characteristics. The egg dimensions also varied as a function of the diet supplied, i.e. high HUFA levels in the broodstock diet resulted in a significant increase of egg diameter, oil globule diameter as well as fertilization rate. Interestingly, the control groups, with the lowest fertilization rate, had the highest hatching percentage, significantly higher than the HUFA/non-vitamin enriched groups. Using non-selected sources of trash fish as a food source at SC resulted in low levels of ascorbic acid (AA) in the eggs compared to the administration of an optimal quality batch of mackerel at FT. Enrichment of the trash fish with ascorbate-2–polyphosphate (ApP) resulted in a tripling of the AA content. Extra enrichment of the FT control diet did not further increase the levels in the eggs, suggesting that a saturation level was obtained. The major fatty acids in turbot eggs as well as freshly hatched larva are 16:0, 18:1ω-9, 20:5ω-3 and 22:6ω-3, but no obvious changes in their pattern could be detected for the different broodstock treatments. However, the level of 20:4ω-6 was significantly higher in the control group of FT, and showed a high correlation with the hatching percentage of the eggs obtained from the various broodstock treatments.

The stress response of the turbot, Scopthalmus maximus (L.), to repetitive factors including netting, air exposure, blood sampling and hand-stripping, were tested using two different tank sizes as well as two blood sampling techniques. Exposure of juvenile fish to air for 1-4 min had no immediate effect on plasma cortisol concentrations or haematocrit values. Similarly, the serial netting of immature fish from tanks did not significantly modify plasma cortisol concentrations, haematocrit or osmolarity values. Hand-stripping of mature males was more disturbing than air exposure. The cumulative effect on plasma cortisol levels and osmolarity of stress factors such as netting, air exposure, blood sampling and stripping applied simultaneously to mature males in a 16 m3 tank and repeated twice daily for several days was recorded. The level of cortisol increased from 5 ng ml-1 to 300 ng ml-1 after 10 days of treatment, while an osmoregulatory imbalance and fish death were observed. Moreover, adaptation of fish to smaller tanks seemed to improve the increased plasma cortisol levels and death rate. Reduction in the number of stress factors applied greatly decreased both the range of physiological responses and the death rate. In order to avoid a cumulative stress response, handling of fish should therefore be reduced to a minimum.

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.

The aim of this study was to compare the total lipid, neutral lipid, phospholipid contents, phospholipid class distribution and fatty acid composition of these lipids in muscle of wild and farmed turbot (Scophthalmus maximus) of similar body size. The results showed that muscle of farmed turbot had a higher lipid content than that of wild turbot (1.06% versus 0.64%) because they contained more neutral lipids (0.52% versus 0.24%) and more phospholipids (0.54% versus 0.40%). Distribution of phospholipid classes in muscle of both wild and farmed turbot was similar with 67–70% phosphatidyl choline, 22–25% phosphatidyl ethanolamine and 4.4–5.2% phosphatidyl inositol plus phosphatidyl serine and 2.4–2.9% sphingomyeline. Compared to wild turbot, all of the lipid classes from farmed turbot contained lower proportions of long chain ω-3 PUFA and 20:4 ω-6 and conversely higher proportions of 20:1 and 22:1. The ratio between ω-3 and ω-6 polyunsatured fatty acids was higher in all the lipid fractions of wild turbot than in those of farmed fish (8.8 versus 4.2 in total lipids, 11.0 versus 3.3 in neutral lipids, 7.9 versus 4.7 in phospholipids). © Rapid Science Ltd. 1998

To evaluate the effects of glutaraldehyde treatment at different disinfection temperatures, Atlantic halibut, Hippoglossus hippoglossus (L.), and turbot, Scophthalmus maximus (L.), eggs, incubated at 5 and 12°C, respectively, were disinfected with 400–1200 mg glutaraldehyde l-1 at three different contact times (2.5, 5 and 10 min). Egg batches of both poor and good quality were tested for halibut. Positive effects were more pronounced in poor than in good-quality batches at hatching. Egg disinfection had a highly positive effect on the viability of yolk-sac larvae in both types of batches. A level between 400 and 800 mg l-1 at a contact time of 5–10 min was optimal for halibut: at lower levels, the bactericidal effect was reduced, and at higher levels, there were indications of toxic effects. Halibut eggs disinfected with optimal doses of glutaraldehyde had furthermore a reduced hatching time and more synchronous hatching as compared with untreated eggs. Turbot was more sensitive to higher doses than halibut, and the best larval performance was obtained for 400–800 mg glutaraldehyde l-1 at a contact time of 2.5 min. A further evaluation should, however, be performed before recommendations are given for species incubated at temperatures higher than 5°C.

Juvenile turbot Scophthalmus maximus (L.), ranging in size from 30 to 407 g were graded into small, large, and unsorted groups in a low-water-level raceway system. Water depth was 7 cm. The rearing design proved self-cleaning and well suited for turbot ongrowing. Mean initial weights 146.2, 236.1, 162.7 g increased to 299.1, 465.6 and 343.1 g in the small, large, and unsorted groups respectively during the 86 day experiment. The corresponding SGRs were 0.84, 0.79 and 0.87% day-1. No positive effect of grading on biomass production was revealed. The coefficient of variance gave no indication of social interactions, but plotting the start weights against estimated individuals SGRs did, although the effect was minor.

The effects of multiple net confinements on the physiological stress response of the turbot (Scophthalmus maximus L.) were investigated. To allow for repeated blood sampling from individuals, fish were cannulated in the afferent branchial artery and were exposed to multiple 9 min net confinement episodes separated by either 4 h or 24 h. In fish stressed twice 4 h apart cumulative effects in plasma cortisol, glucose and free fatty acid concentrations were evident after the second handling stress. Although plasma Na+ and Cl− concentrations were not increased further by the second net confinement, the elevation in plasma concentrations were more sustained compared to turbot handled only once. In a second experiment where turbot were net confined five times, with a 24 h recovery period between each net confinement episode, there was no evidence of any physiological accommodation with repeated exposures. For most circulatory parameters, there was also no evidence of any cumulative effect apparent. Plasma glucose concentrations were, however, elevated to a significantly higher degree with repeated net confinements. Although turbot were tolerant to the handling procedures, with no mortalities recorded, episodes of multiple handling of this species should be separated by at least 24 h if cumulative physiological disturbances are to be avoided. The significance of cumulative increases in plasma glucose concentrations is discussed.

Before transfer to larval incubators, water was membrane filtered to remove >95% of the bacteria and then transiently maintained in a biofilter that promoted recolonization of the water by non-opportunistic bacteria. The process is termed microbial maturation of the water. Hypothetically the bacterial flora in the matured water should protect the marine larvae from colonization and proliferation by opportunistic bacteria. Testing of the hypothesis demonstrated 76% higher survival of yolk sac larvae of Atlantic halibut (Hippoglossus hippoglossus) in matured than in membrane filtered water. Proliferation of opportunistic bacteria was observed in the rearing water after hatching of turbot eggs (Scophthalmus maximus), but to a less extent in the microbially matured water. In the early phase of first feeding of turbot larvae, the matured water induced qualitative differences in the gut microflora. Significantly higher initial growth rate of the turbot larvae in the matured water affected 51% higher average weight of 13 days old larvae than in membrane filtered water. Algal addition to the matured water enhanced the larval growth further. The experiments conducted supported the proposed hypothesis that microbial maturation selects for non-opportunistic bacteria, which protects the marine larvae from proliferation of detrimental opportunistic bacteria.

Turbot fry (10–20 mm) and juveniles (85–110 mm) were transferred directly from 16.0–16.5 ‡C to 1.0 ‡C, 2.5 ‡C, 5.5 ‡C or 8.0 ‡C seawater. The fry were more sensitive to cold water than juveniles. The fry survived for 1 week at 8.0 ‡C but not at 5.5 ‡C, whereas juveniles survived at 5.5 ‡C but not at 2.5 ‡C. Transfer of juveniles to 1.0 ‡C and 2.5 ‡C seawater caused a high mortality, a marked increase in plasma Cl- concentration, decrease in muscle water content, and hyperglycaemia. Acclimation to 5.5 ‡C (juveniles) or 8.0 ‡C (fry and juveniles) markedly reduced the sensitivity to 1.0 ‡C exposure.

The effect of different lipid compositions of live feed on the survival, growth rate and pigmentation success of turbot larvae, Scophthalmus maximus (L.), was investigated. Rotifers, Brachionus plicatilis, together with the algae Tetraselmis sp., were administered until day 12, and Artemia was fed until day 27. The experimentally treated live feeds were enriched with four formulated emulsions, resulting in a gradient in the relative contents of Ω3 HUFA (highly unsaturated fatty acids) and in DHA (docosahexaenoic acid, 22:6 Ω3)/EPA (eicosapentaenoic acid, 20:5 Ω3) ratios in both the rotifers and Artemia.

There is a need for a standard in vitro procedure to infect larval fish with bacteria. Such a procedure could be used as a tool to evaluate fish quality, verify fish sensitivity to a certain bacterial strain or evaluate the pathogenicity of a bacterium towards a given fish species. The availability of a challenge test is a prerequisite in studies dealing with the effect of different medicinal treatments on diseased fish. An oral challenge test would offer the possibility to investigate the routes of infection via the digestive tract, i.e. after feeding contaminated feeds. The present study aims to verify this hypothesis and proposes a standard challenge procedure for turbot (Scophthalmus maximus) larvae with a pathogenic Vibrio anguillarum strain.