Time of first feeding of Atlantic halibut, Hippoglossus hippoglossus L., larvae

Atlantic halibut, Hippoglossus hippoglossus (L.), eggs originating from one female were evenly distributed between four silos (4.8 m³) shortly prior to hatching. At days 30, 35, 40 and 44 after hatching [i.e. 200, 230, 260 and 290 day-degrees (days^o)], the larvae were successively collected and transferred to indoor start feeding tanks, and larvae were offered a diet of instar II Artemia nauplii which had been enriched short time (24 h). A significant correlation was found between the age of the larvae and onset of first feeding. The larvae transferred to start-feeding incubators at 290 days^o were able to capture Artemia only a few hours after transfer, whereas it took 6 days for the larvae transferred at 200 days^o to reach a corresponding ingestion level. Larval growth was also positively correlated to both larval age and prey consumption. However, there were no differences in survival between the larval groups.     

A tank design for first feeding of Atlantic halibut, Hippoglossus hippoglossus L., larvae

An intensive method of juvenile Atlantic halibut, Hippoglossus hippoglossus (L.), production has been under development over the last decade because of the problems associated with the extensive method. The lack of initiation of feeding behaviour has been the main obstacle for successful indoor rearing under artificial light and feeding conditions. In the present paper, an intensive method for the first feeding of halibut larvae is described and verified by practical feeding trials. The method involves circular 1.5-m³ indoor tanks with a peripheral ring-shaped cover, the use of continuous light, UV-A radiation during the first 24 h, central up-welling of water made by aeration and the use of microalgae in the rearing water. The single most important factor in such systems is to maintain a current pattern which allows the larvae to orientate and position themselves to face the water current for easy capture of prey.     

A formulated diet for Atlantic halibut (Hippoglossus hippoglossus, L.) larvae

A diet for Atlantic halibut-larvae was formulated taking into account the fact that marine-fish larvae have a limited ability to assimilate protein and lipid. Dietary protein consisted of a free amino-acid premix (7.2% of crude protein), predigested-squid mantle (7.2%), squid mantle (8.6%) and cod-muscle mince (77.0%). Lipid sources were soyabean lecithin (33% of crude lipids), crude phospholipids extracted from cod roe (10%) and sardine oil (57%). Larvae were weaned onto the experimental diet at wet-body weights of 0.07, 0.10 or 0.16 g, respectively. The experimental diet was fed for 31, 25 or 17 days, respectively, and the experiment was terminated on the same calendar day for all groups. A control group was fed with Artemia nauplii enriched with DHA Selco™ from 0.07 g. Survivals ranged from 78% in larvae transferred at 0.10 g to 96% in those transferred at 0.16 g and in the control group. Daily specific-growth rates (SGR) were 3.1 ± 0.07, 3.3 ± 0.11 and 2.2 ± 0.01% day⁻¹ in larvae transferred at 0.07, 0.10 and 0.16 g, respectively, while growth in the control group was 5.1% day⁻¹. It was concluded that weaning of Atlantic-halibut larvae is feasible from 0.7 g (approximately 20 days post first-feeding) when the formulated diet contains predigested protein and ample amounts of phospholipids.     

Design and operation of Atlantic halibut, Hippoglossus hippoglossus L., egg incubators

An egg incubator system specially designed to meet the requirements of Atlantic halibut, Hippoglossus hippoglossus L., eggs is described. Compared to other pelagic marine fish eggs, halibut eggs are frequently found to be heavy and lacking in buoyancy in seawater incubators. The biological features of halibut eggs which explain the choice of system design are discussed. In addition to the biological requirements, the system described is designed to meet the demands of commercial hatcheries where handling of large egg masses with a minimum of labour is needed. The incubation method has proved by experience to give high survival rates throughout egg development.     

Atlantic halibut, Hippoglossus hippoglossus L., larvae cultivation literature, including a bibliography

The first attempts to rear Atlantic halibut, Hippoglossus hippoglossus L., larvae were carried out in Norway in the period from 1974 to 1980, when ripe adult specimens of Atlantic halibut were net-caught, and stripped for eggs and milt. Both incubation of yolk-sac larvae and first-feeding were carried out in large submerged plastic bags and the larval food consisted of natural zooplankton collected from surrounding lagoon water. This semi-extensive production method was further developed and led to the establishment of several commercial production trials by the end of the 1980s. During recent years, research has been focused on intensive methods for first-feeding and the combined effort of several research institutes has resulted in a reliable production method. During the late 1980s and early 1990s, the main research activity was focused on the biology of and rearing techniques for eggs and yolk-sac larvae. These techniques provided satisfactory yields for several years. However, during the past few years, a certain decrease in survival through the yolk-sac stage has been experienced at several hatcheries. Since the early 1990s, the first-feeding period has represented the bottleneck in the development of a reliable rearing method. The main effort has been concentrated on system configuration and on improving live prey quality. In the future, new feeding strategies including further improvement of live prey (i.e. Artemia), the use of copepods and early weaning onto a formulated diets should be emphasized. Further research on hygiene and technological improvements is needed to increase growth and survival through metamorphosis.     

Effects of light administration and algae on first feeding of Atlantic halibut larvae, Hippoglossus hippoglossus (L.)

The aim of the study was to investigate the effects of two light regimes that independently had shown positive effects on feeding and growth in cultures of Atlantic halibut, Hippoglossus hippoglossus (L.), larvae. The regimes were low-intensity overhead light and submerged light at intermediate light intensities. Secondly, an alleged beneficial effect of algae was investigated. An experiment was designed to include four different regimes in the larval cultures: low-intensity overhead light with and without algae (Tetraselmis sp.), and submerged light with and without algae. The results showed that submerged light was superior to overhead light with respect to larval growth, survival and feeding incidence. It was further indicated that algae improved larval growth and survival, but no effect was shown on feeding incidence. There was, however, no interaction between the effects of algae and those of the light regime. The causal effect of the algae may be ascribed to indirect factors, such as light attenuation as well as a direct and indirect nutritional effect.     

The effects of feeding frequency on growth of juvenile Atlantic halibut, Hippoglossus hippoglossus L.

Four experiments were conducted to investigate the effects of feeding frequency on growth of juvenile Atlantic halibut, Hippoglossus hippoglossus L. Fish (22–75 g) fed three (3 ×) or five times per day (5 × day^?1) under constant light and temperature (13±1°C) consumed significantly more feed than fish fed 1 × day^?1 but by the end of the experiment only fish fed 5 × day^?1 were heavier and had greater specific growth rates (SGR). Under simulated winter conditions (9L:15D, 5±1°C), halibut (～300 g) fed every other day consumed more feed, had a greater SGR and final weight compared with fish fed every third day. Feed conversion ratios were not different among treatment groups in any of the experiments. These results suggest that growth rates may be improved by feeding juvenile halibut more than 1 × day^?1.     

Feeding strategies to achieve correct metamorphosis of Atlantic halibut, Hippoglossus hippoglossus L., using enriched Artemia

Atlantic halibut, Hippoglossus hippoglossus L., larvae were reared under four different Artemia feeding regimes for 40 days from day 20 post first feeding. Three Artemia enrichments were used: Super Selco? (SS), AlgaMac 2000? (AM) and a particulate mix of AlgaMac 2000? with tuna orbital oil (TOO/AM). The SS and AM Artemia were tested in three different combinations: (1) a 1:1 ratio continuously to day 60 (AM/SS); (2) a 1:1 ratio to day 41, then AM only (AM/SS-41): and (3) AM only to day 41, then a 1:1 ratio (AM-41). The fourth treatment comprised TOO/AM Artemia, which was fed continuously. At day 60 post first feeding, measurements were made of survival and growth rates, postmetamorphic characteristics (i.e. eye migration and pigment distribution), and lipid composition. The mean survival rates ranged from 65.1% to 84.5%. Specific growth rates varied from 7.64 to 8.13. The eye migration indices were between 2.3 and 2.6. These parameters did not differ significantly among treatments (P 0.05). A significantly greater proportion of fry (P<0.05) exhibited‘perfect metamorphosis’(correct pigment distribution and complete eye migration) in the AM/ SS-41 and AM-41 treatments (59.8 ± 3.03% and 54.6 ± 1.08%, respectively) compared to the AM/SS and TOO/AM treatments (35.9 ± 4.02% and 39.9 ± 6.43%, respectively). The fatty acid compositions of livers and eyes varied according to feeding regime, but did not correspond to the metamorphosis characteristics of the fry.     

Economic evaluation of a stratified transport method for Atlantic halibut (Hippoglossus hippoglossus) juveniles

The objective of this study was to evaluate a convenient, low-cost modification to conventional transfer methods for Atlantic halibut juveniles. A series of wire mesh cages were stacked within transport tanks creating a stratified transport system (STS), increasing the surface area for settlement and facilitating a more homogeneous distribution of halibut throughout the tank compared with the conventional insulated box (Unstructured, UTS). A stochastic cost-benefit analysis determined investment into a STS to be cost-effective, generating a mean benefit-cost ratio of 1.31 (95% CI, 0.68?C2.00) after 2?years and a mean 5-year net present value of $85,176 (95% CI, $46,906?C$125,630). The implementation of a STS was found to be technically feasible and economically efficient method to improve Atlantic halibut transport.     

Suitable methods for cryopreservation of semen from Atlantic halibut, Hippoglossus hippoglossus L.

Decrease in the quality and quantity of Atlantic halibut, Hippoglossus hippoglossus L., semen towards the end of the reproductive season hampers production of good-quality embryos. Therefore, cryopreservation of spermatozoa is a method showing potential to facilitate controlled reproduction in Atlantic halibut. The present study aimed at establishing the appropriate cryopreservation procedure. We tested 20 extenders composed of four various diluents and five cryoprotectants (DMSO, DMA, methanol, propylene glycol, and glycerol) to determine the best extender. Then, we examined cryopreservation quality using various methods of loading and various volumes of cryopreserved samples. In most of the tested variants, sperm diluted with an extender showed high motility after 24-h incubation despite the high osmotic pressure of the extender. Modified turbot extender (MTE) was the best of the tested diluents, securing the highest post-thaw motility (P < 0.05), and DMSO, DMA, and methanol were the best cryoprotectants (P < 0.05). There was no significant effect of 15-min equilibration of semen in MTE-based extenders prior to freezing on post-thaw motility (P > 0.05). MTE-based extender was chosen as the most suitable. Semen cryopreserved in straws, Eppendorfs or Ziploc bags in volumes ranging from 0.25 to 20 ml showed similar high fertilization ability. Survival of larvae produced with the cryopreserved sperm did not differ from controls produced with freshly collected sperm. Motility 3 h after thawing was high but depended on the type of cryoprotectant and the volume of cryopreserved sperm (P < 0.05). The developed cryopreservation procedure has been applied at our Atlantic halibut breeding station for seed production.     

Conversion of β-carotene, canthaxanthin and astaxanthin to vitamin A in Atlantic halibut (Hippoglossus hippoglossus L.) juveniles

Larval Atlantic halibut fed Artemia has previously been shown to contain lower levels of Vitamin A compared to larvae fed zooplankton. The two types of live prey contain small or no amounts of vitamin A, but high levels of carotenoids that can be converted to vitamin A in other fish species. The purpose of this study was to investigate the ability of Atlantic halibut juveniles to convert β-carotene, astaxanthin and canthaxanthin to vitamin A. Three levels of each carotenoid and retinyl acetate were fed to Atlantic halibut juveniles for 60 days. A vitamin A and carotenoid deficient diet was fed in triplicate as control. A HPLC method modified from Nöll (1996) and validated for fish matrix was used to quantify both all-trans-retinol and 3,4-didehydro retinol. By comparing regression coefficients we observed that the increasing levels of carotenoids in the diets were reflected in increasing levels of vitamin A in both whole fish and liver samples. All carotenoids were converted to vitamin A, but to different degrees. Retinyl acetate and β-carotene resulted in whole fish vitamin A levels significantly higher than canthaxanthin and astaxanthin. 3,4-didehydro retinol was not detected when the overall level of all-trans-retinol was low. When 3,4-didehydro retinol appeared, it was always in lower levels than all-trans-retinol.     

The effect of light on activity and growth of Atlantic halibut, Hippoglossus hippoglossus L., yolk-sac larvae

The growth and activity of Atlantic halibut, Hippoglossus hippoglossus L., yolk-sac larvae exposed to light of differing intensities and wavelengths were investigated every fifth day. The experiments were conducted at 6 ^oC from day 1 until day 34 post hatch. Four intensities of constant white light (2.0, 0.3, 0.03 and 0.005 μ Em^?2 s^?1, λ_max 590 nm), and constant coloured light of equal intensities (0.03μ Em^?2s^?1) in the blue, green and red spectrums (λ_max 450, 560 and 670 nm, respectively) were used. In addition to a control treatment in constant darkness, one treatment was incubated in a 12:12 h light: dark photoperiod. The light treatments did not have any discernible effect on the total length, myotome height, dry weights or yolk conversion efficiencies. The most intense white light resulted in an increased activity on days 24 and 30 post hatch, resulting in a temporarily reduced length and myotome height for the larvae in these groups compared to the other treatments. Larvae from all treatments were of the same size 34 days post hatch. The dry weights of the larvae and yolk-sacs were unaffected by light treatment. The activity increased independently of light treatment until 120 degree-days, and thereafter, the strongest white light resulted in an temporarily increased activity. The distribution of activity changed independently of light regime in the beakers during development.     

Folate in eggs and developing larvae of Atlantic halibut, Hippoglossus hippoglossus L.

Folate mobilization from the yolk compartment during larval development was studied by analysing the folate concentration in whole body, embryo and yolk in a single batch of Atlantic halibut, Hippoglossus hippoglossus L., eggs and larvae that showed successful fertilization and development. There was a net loss of approx. 50% of folate from yolk during endogenous feeding. Further, only 23% of the decrease in yolk folate was retained in the larval body. The data suggest a need for folate for metabolic and growth purposes during embryogenesis of approximately 2 μg g^?1 weight gain. Relative to these data and published folate requirement for cold‐water species, batches of egg from 16 Atlantic halibut brood fish contained variable and, for some batches, critically low levels of folate. This may constitute a potential problem for larval development until start feeding.     

The karyotype of the Atlantic halibut, Hippoglossus hippoglossus (Linnaeus)

The karyotype of the Atlantic halibut, Hippoglossus hippoglossus, (Linnaeus, 1758) consists of 24 pairs of chromosomes (2n= 48) all of which are subtelocentric or acrocentric. The number and morphology of the chromosomes of the Atlantic halibut is therefore similar to most other pleuronectid fish studied.     

A note on the behaviour of adult Atlantic halibut, Hippoglossus hippoglossus (L.), in cages

Abstract. Observations of adult Atlantic halibut, Hippoglossus hippoglossus (L.), behaviour in cages were made with underwater camera and video recording equipment. Significantly more fish ( P < 0·01) were found on the cage bottom than in the water column, fish tending to congregate around the outside rather than in the centre of the cage. During rough weather, the cage bottom was observed to heave violently and proportionately fewer fish remained on the bottom, those which did adopting an arched body posture with heads and tails not in contact with the cage bottom. Around 25% of the caged fish were active at any time, most of the active fish remaining close to the cage surface or bottom, with little use being made of the remaining cage volume. Fish were observed to swim in a circular pattern close to the cage walls (mean velocity 0·53 m/s), maintaining such behaviour for periods of up to 5min with little change in swimming speed. Whilst all food types were ingested, items delivered directly lo the cage bottom were taken only if detected within the first minute or so. The implications for rearing Atlantic halibut in conventional cages are discussed.     

A correlation between phototactic response and first-feeding of Atlantic halibut (Hippoglossus hippoglossus L.) larvae

The correlation between positive phototaxis and feeding incidence at first‐feeding for groups of Atlantic halibut larvae ranging in age from 210 to 240 degreedays, post hatch, was examined. Phototactic response was measured as the fraction of larvae that responded by horizontal swimming towards a light source, and the median travel distance for the responding fraction of larvae. Within the ranges investigated, larval age, size or proportion of deformed larvae had no significant effect on the phototactic response, or on the feeding incidence (deformed larvae excluded from analysis). The fraction of larvae responding phototactically and the median travelling distance for responding larvae were significantly correlated. Feeding incidences after 24 and 48 h were also significantly correlated with both measures of phototactic response. The possibility of using phototactic response in quality assessment is discussed.     

Pharmacokinetic and efficacy studies on bath-administering potentiated sulphonamides in Atlantic halibut, Hippoglossus hippoglossus L.

The uptake, metabolism, tissue distribution and excretion of four sulphonamides and trimethoprim following bath treatment of Atlantic halibut, Hippoglossus hippoglossus L., were studied. Bath treatment using a concentration of 200 μg ml^–1 for 72 h resulted in peak sulphadimidine concentrations in muscle and abdominal organ homogenates of 32·6 and 68·2 μg g^–1, respectively. The corresponding values were 24·4 and 73·4 μg g^–1 for sulphaguanidine, 6·1 and 45·1 μg g^–1 for sulphamethoxazole, 2·1 and 15·1 μg g^–1 for sulphadimethoxine, and 99 and 169 μg g^–1 for trimethoprim. After a 72-h treatment, approximately 90% of the sulphadimethoxine and sulphamethoxazole present in tissues was found as the N⁴-acetylated metabolite, whereas for sulphadimidine and sulphaguanidine, the N⁴-acetylations were from 9 to 23%. Based on these preliminary absorption studies, sulphadimidine was chosen as the companion sulphonamide to trimethoprim. Using a combination of 500 μg ml^–1 sulphadimidine and 100 μg ml^–1 trimethoprim in the bath for 72 h, peak muscle and liver concentrations of 262 and 312 μg g^–1, respectively, for sulphadimidine and 32·8 and 83·6 μg g^–1, respectively, for trimethoprim were achieved. Elimination half-lives (t_1/2β) for sulphadimidine were calculated to be 35 and 48 h for muscle and liver, respectively. The corresponding values for trimethoprim were 98 and 116 h. Using the 95% confidence limit for single observations (95% prediction limit) and a maximum residue limit (MRL) value of 0·05 μg g^–1 for trimethoprim and 0·1 μg g^–1 for sulphadimidine, the elimination times (E_t95) for muscle and liver were calculated to be 18 and 26 days, respectively, for sulphadimidine and 40 and 55 days, respectively, for trimethoprim. Minimum inhibitory concentrations (MIC) values against selected strains of Vibrio sp. were equal to or above 128 μg ml^–1 for sulphadimidine, between 0·25 and 4·00 μg ml^–1 for trimethoprim and between 0·4 and 8·8 μg ml^–1 for various ratios of the sulphadimidine:trimethoprim combination. In the tested ratios, the combined antimicrobial action of trimethoprim and sulphadimidine were synergistic, as revealed by their fractional inhibitory concentration (FIC) indices. In general, the 1:5 trimethoprim sulphadimidine ratio showed the highest degree of synergism. Using a combination of 500 μg ml^–1 sulphadimidine and 100 μg ml^–1 trimethoprim in the bath for 72 h, concentrations greater than a MIC value of 0·8 μg ml^–1 were maintained for 22 days in muscle and 29 days in liver. In a laboratory challenge experiment using Vibrio anguillarum strain HI 11347, a significantly lower mortality was observed in the drug-treated group (40%) compared to the untreated control group (93%).