Halibut Farming Research Articles

Using fatty acid markers to distinguish between effects of salmon ( Salmo salar ) and halibut ( Hippoglossus hippoglossus ) farming on mackerel ( Scomber scombrus ) and whiting ( Merlangius merlangus )

Presence of coastal aquaculture activities in marine landscapes is growing with impacts on the wild fish that share these habitats. However, it is difficult to disentangle subsequent ecological interactions between these activities and marine fish communities. We evaluated the impact of both salmon and halibut farms on mackerel (Scomber scombrus) and whiting (Merlangius merlangus) sampled near sea cages using condition indices and fatty acid (FA) biomarkers. Results of the stomach content analysis indicated that mackerel and whiting consumed waste feed which was also reflected in their modified FA profiles. Both mackerel and whiting had elevated levels of FAs that are of vegetable oils origin. The use of vegetable oils as replacement for marine oils is a lot more common in salmon farming than halibut farming. Additionally, the overall effects of the two fish farms were more pronounced in whiting than in mackerel sampled near the sea cages. By allowing discrimination between sources of trophic interactions, this method could lead to more informed decisions in managing different farming activities.

Pharmacokinetic profiles of florfenicol in spotted halibut, Verasper variegatus, at two water temperatures.

The pharmacokinetic profiles of florfenicol in the spotted halibut (Verasper variegatus) were investigated at 15 and 20°C water temperatures, respectively. Florfenicol content in plasma samples was analyzed using an HPLC method. Drug concentration versus time data were best fitted to a three-compartment model after a single intravenous administration (15mg/kg BW), and fitted to a two-compartment model after an oral administration (30mg/kg BW) at 15 and 20°C. The florfenicol concentration in the blood increased slowly during the 12hr following an oral administration at 15°C, with a peak concentration (Cmax ) of 9.1mg/L, and then declined gradually. The half-lives of absorption, distribution, and elimination phase were 2.18, 5.66 and 14.25hr, respectively. The bioavailability (F) was calculated to be 24.14%. After an oral administration at 20°C, shorter half-lives of absorption (1.33hr), distribution (2.51hr) and elimination (9.71hr), a higher Cmax (12.2mg/L), and a similar F (23.98%) were found. Based on the pharmacokinetics and pharmacodynamics, an oral dose of 30mg/kg BW was suggested to be efficacious for bacterial disease control in spotted halibut farming.

Marine finfish effluent bioremediation: Effects of stocking density and temperature on nitrogen removal capacity of Chondrus crispus and Palmaria palmata (Rhodophyta)

Optimal stocking density of the marine red algae Chondrus crispus and Palmaria palmata was determined to maximize productivity and nitrogen removal in a land-based Atlantic halibut farm. Both species were cultured at 0.2, 2, 4, 6 and 10kgm−2 for four weeks at 140±10μmolphotonsm−2s−1 of photosynthetically active radiation (PAR) and 16:8 L:D photoperiod. For each species, two rearing temperatures were compared at different times of the year: 6 (Dec.) and 13°C (June) for C. crispus, and 6 (Mar.) and 16°C (July) for P. palmata. Growth rates of both species were inversely dependent on stocking density at all temperatures; however, the productivity (gfresh weightd−1) in Chondrus was significantly higher at 2kgm−2 than 0.2kgm−2 at both temperatures. By contrast, productivity of Palmaria was independent of stocking densities of 0.2 through 6.0kgm−2 at both temperatures. The net N removal in Chondrus was the highest at 2.0kgm−2 at both temperature conditions. Palmaria also showed the highest N removal at 2.0kgm−2 at 6°C but at 4.0kgm−2 at 16°C. Overall, C. crispus was the better performer year-round than P. palmata in terms of productivity and nutrient removal capacity.

Bioremediation potential of Chondrus crispus (Basin Head) and Palmaria palmata: effect of temperature and high nitrate on nutrient removal

To evaluate the nutrient removal capabilities of two red macroalgae, apical blades were cultured in the lab for 4 weeks at either 6, 10, or 17°C and nitrate at either 30 or 300 μM, typical of the seasonal range of conditions at a land-based Atlantic halibut farm. Stocking density was 2.0 g L−1, irradiance 125 μmol photons m−2 s−1, photoperiod 16:8 (L:D), and nitrogen to phosphorus ratio 10:1. For both species, the highest growth rate was at 300 μM NO3− with Palmaria palmata growing fastest at 6°C, 5.8% day−1, and Chondrus crispus growing best at 17°C, 5.5% day−1. Nitrogen and carbon removal by P. palmata was inversely related to temperature, the highest rate at 6°C and 300 μM NO3− of 0.47 mg N and 6.3 mg C per gram dry weight per day. In contrast, C. crispus removal of N was independent of temperature, with mean removal of 0.49 mgN gDW−1 day−1 at 300 μM NO3−. The highest carbon removal by C. crispus was 4.4 mgC gDW−1 day−1 at 10°C and 300 μM nitrate, though not significantly different from either 6 or 17°C and 300 μM nitrate. Tissue carbon:nitrogen ratios were >20 in both species at 30 μM nitrate, and all temperatures indicating nitrogen limitation in these treatments. Phycoerythrin content of P. palmata was independent of temperature, with means of 23.6 mg gFW−1 at 300 μM nitrate. In C. crispus, phycoerythrin was different only between 6°C and 17°C at 300 μM nitrate, with the highest phycoerythrin content of 12.6 mg gFW−1 at 17°C. Morphological changes were observed in P. palmata at high NO3− concentration as curling of the fronds, whilst C. crispus exhibited the formation of bladelets as an effect of high temperature.

Eye health in juvenile Atlantic halibut, Hippoglossus hippoglossus L., at two commercial production densities

Eye damages have been known to occur in commercial halibut farming, and are expected at elevated biomass densities. As one part of intensifying halibut production, the present study was performed to investigate the effect of biomass density on growth and eye health of juvenile (14.4 g) halibut, Hippoglossus hippoglossus L., reared commercially at two densities; normal (12.5 kg m − 2 ) and high (18.2 kg m − 2 ) density for 18 wks. At start and three sampling points, growth, mortality, eye health and cataract score were recorded, and since histidine status has been related to eye health in farmed Atlantic salmon, lenses and white muscle were sampled for analysis of free histidine amino acids (imidazoles). No differences in growth and mortality were found between the two densities during the experiment. Cataractous changes did not occur, while the incidence of eye damage increased to eventually affect 33% and 23% of the fish reared in normal and high density, respectively. High lens and muscle free imidazole concentrations support the finding of no cataract in the present study. We conclude that the higher fish density under the present rearing conditions does not impact feeding and growth, and rather reduce the development of eye damages in juvenile halibut. The present hyper oxygenated inlet water (151% O 2) at high water flow may be a production factor in the formation of gas bubbles and damages in the eyes.

Long-Term Rearing of Atlantic Halibut at Intermediate Salinity: Effect on Growth, Feed Conversion Efficiency, and Blood Physiology

The long-term effects of two salinities (15 and 27‰) on growth, feed conversion efficiency, and blood physiology of Atlantic halibut were investigated. Growth and feed conversion efficiency of juvenile Atlantic halibut was improved by 20% by rearing fish at intermediate salinities (here 15‰). Interestingly, the growth-enhancing effect of lowering the salinity seems to be independent of size and age of the halibut and is not reserved to the initial juvenile stage. A cost benefit analysis indicates that the new farming method has the potential to double the profit of a given halibut farm. Measured blood variables were lower at 15‰ compared with 27‰ while the values were within the range of that earlier described and there were no indications that reduced salinities represented a stressful environment to the fish. Overall, the results indicate that the growth rate, feed conversion, and farming economics can be improved by rearing Atlantic halibut at near intermediate salinities.

Individual behaviour and growth of halibut ( Hippoglossus hippoglossus L.) fed sinking and floating feed: Evidence of different coping styles

A crucial problem in halibut farming is low and variable growth during the on-growing phase. Individual halibut may have different abilities to adapt to different aspects of the farming environment, including the feed distribution mode. In this study, 30 individually tagged halibut (mean weight 1.5 kg) were moved from a larger tank and kept for 3 months in six 7 m 3 tanks with five fish in each tank. Individual feed intake and behaviour were compared in two periods, when either sinking or floating food was offered. Individual fish within a tank showed large variations in behaviour and feed intake, but both individual swimming behaviour and feed intake were positively correlated between periods. On the basis of differences in stereotypic surface swimming activity and feed intake, the halibut were classified in four behaviour categories that were suggested to reflect reactive or proactive stress coping styles. Floating food seemed to be an additional stressor and decreased feeding and increased stereotypic swimming activity. When floating food was replaced by sinking food, proactive fish that exhibited frequent surface swimming turned into “well-adapted” fish. The indication of different coping styles in individual halibut and the ability of fish applying a stress coping style to adapt when the situation changes suggests the possibility of improving halibut farming by both selective breeding and tailoring the tank environment to the demands of the fish.

Chilled storage of semen from Atlantic halibut, Hippoglossus hippoglossus L. II: Effect of spermiation advancement, catheterization of semen, and production-scale application

A method for in vitro storage of Atlantic halibut Hippoglossus hippoglossus L. semen can facilitate seed production. The study aimed at determining the effect of male spermiation advancement on viability of chilled stored spermatozoa. The use of catheterization of semen from the sperm duct was examined. Also, large volumes of semen were stored under sub-optimal production-like conditions in order to determine the suitability of the method into practical use. Semen was collected from two broodstocks: natural photoperiod males, being at the first phase of the reproductive season and 3-month advanced photoperiod males, being at the end of the reproductive season. Semen samples were diluted 1:5 (v/v) with modified Hanks’ Balanced Salt Solution supplemented with antibiotics, and stored in Ziploc bags filled with air. Sperm motility parameters, assessed by computer-assisted sperm analysis (CASA), were assessed weekly. Experimental and production-scale fertilization trials were performed. Sperm samples from natural photoperiod males showed significantly longer viability under in vitro storage conditions than sperm from advanced photoperiod males. In the natural photoperiod group, the decrease in spermatozoa motility, curvilinear velocity and straight-line velocity occurred on day 50, 14, and 28 of storage, respectively. Spermatozoa from one of five males were still motile on day 80 of storage, and fertilization rates and embryo survival rates obtained using semen stored for 70 days did not differ from control values and they were significantly higher than values obtained with the use of fresh semen of the same male, but being at the end of reproductive season. Catheterization of semen showed no advantage to stripping the semen without a catheter, even for samples stored undiluted for 1 day of collection, before dilution. Under sub-optimal conditions, spermatozoa stored in large volumes (10–100 mL of diluted semen) without any special treatments except for weekly swirling, remained viable for more than 1 month. Production-scale fertilizations with samples stored for 5–21 days resulted in high survivals of embryos and hatchlings. Because of its simplicity and efficiency, the method shows a high potential for use in commercial Atlantic halibut farming. It has already been applied to a halibut breeding programme for the next reproductive season at our research station.

Pericarditis and myocarditis in farmed Atlantic halibut Hippoglossus hippoglossus.

Farming of Atlantic halibut Hippoglossus hippoglossus is a growing industry in Norway. This study comprises the first description of heart morphology in fish from one Atlantic halibut farm. Fish with no clinical signs of disease were randomly sampled (8 to 12 mo old, weight 1 to 50 g). The hearts were studied by light and electron microscopy and samples were taken from the kidney and pericardial cavity for bacteriological examination. Slight to severe changes were found in most hearts at all samplings. The most serious pericardial and myocardial changes were seen in larger fish (15 to 50 g). In some of the hearts the affected pericardium formed multifocal protrusions. Eight fish had an adhesion between the apex of the ventricle and the parietal wall of the pericardial cavity. Results of bacteriology and immunohistochemistry investigations for common disease agents were negative.

Vaccination of Atlantic halibut Hippoglossus hippoglossus L., and spotted wolffish Anarhichas minor L., against atypical Aeromonas salmonicida

Atypical furunculosis caused by atypical Aeromonas salmonicida is an increasing problem in commercial halibut farming, and a potential problem in farming of spotted wolffish in Norway. Halibut, Hippoglossus hippoglossus L., and spotted wolffish, Anarhichas minor L., vaccinated with oil-emulsified vaccines against atypical furunculosis, demonstrated a relative percent survival (RPS) of approximately 90 when challenged with homologous isolates. Bath and aqueous injection vaccines failed to protect against disease when challenged 10 weeks post-vaccination. High antibody titres were produced in both species after vaccination with oil-emulsified vaccines, and the major antibody response were against A-layer, LPS and some minor outer membrane (OM) proteins.