A pilot study of halibut larvae (Hippoglossus hippoglossus L.) reared from start feeding to metamorphosis on diets of wild zooplankton and Artemia

Halibut larvae ready to start feed were placed in two outdoor tanks of 7 m^3. The larvae in one tank were fed wild zooplankton throughout the whole period, and the larvae in the other tank were fed wild zooplankton from day one to day seven and Artemia thereafter. Measurements of growth, gut content and content of fatty acids were made of the larvae. Number and species of phytoplankton and zooplankton, as well as abiotic parameters were measured during the experiment. Larval myotome height and dry weight were significant higher for the group supplied wild zooplankton and Artemia than for the group supplied only wild zooplankton, at day 22 after first feeding. For the larval group supplied only wild zooplankton the myotome height and length, at day 43 (the end of the experiment), were significant higher than the group supplied both wild zooplankton and Artemia. Fatty acids analysis did not show significant differences between the larvae in the two feeding groups. There was not observed differences in larval pigmentation either

Sensitivity towards elevated pCO2 in great scallop (Pecten maximus Lamarck) embryos and fed larvae

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Differential developmental toxicity of crude oil in early life stages of Atlantic halibut (Hippoglossus hippoglossus)

To further understand the complexity of developmental toxicity of dispersed oil and importance of exposure timing on fish early life stages, Atlantic halibut (Hippoglossus hippoglossus) were exposed to environmentally relevant concentrations through two embryonic developmental windows: the first period occurred during the epiboly process (named as “early embryonic exposure”) and the second period overlapped the ontogenesis and cardiogenesis processes (named as “late embryonic exposure”). Following 72 hour oil exposure, embryos were transferred to clean seawater and a toxicity screening was performed in the yolk-sac larvae until first-feeding stages (56 days). The current study demonstrated that the exposure timing is essential for the development of toxic effects of crude oil in Atlantic halibut. Neither embryonic exposures (early or late) showed notable acute toxicity during exposure, yet both showed global latent teratogenic effects during yolk sac stages. Fish exposed during organogenesis (late) displayed stronger and more severe toxic effects than fish exposed during epiboly process (early), including reduced condition, severe craniofacial deformities and cardiovascular disruptions. The uptake level of polycyclic aromatic hydrocarbons into larval tissue and metabolic activity were greater following the late embryonic exposure and remained high during the depuration period at the highest exposure concentration. Overall, the long yolk sac stage development timing of Atlantic halibut makes this species a good candidate for evaluation of embryonic crude oil toxicity and its mechanisms.publishedVersio

Functional modifications associated with gastrointestinal tract organogenesis during metamorphosis in Atlantic halibut (Hippoglossus hippoglossus)

Background: Flatfish metamorphosis is a hormone regulated post-embryonic developmental event that transforms a symmetric larva into an asymmetric juvenile. In altricial-gastric teleost fish, differentiation of the stomach takes place after the onset of first feeding, and during metamorphosis dramatic molecular and morphological modifications of the gastrointestinal (GI-) tract occur. Here we present the functional ontogeny of the developing GI-tract from an integrative perspective in the pleuronectiforme Atlantic halibut, and test the hypothesis that the multiple functions of the teleost stomach develop synchronously during metamorphosis. Results: Onset of gastric function was determined with several approaches (anatomical, biochemical, molecular and in vivo observations). In vivo pH analysis in the GI-tract lumen combined with quantitative PCR (qPCR) of α and β subunits of the gastric proton pump (H+/K+-ATPase) and pepsinogen A2 indicated that gastric proteolytic capacity is established during the climax of metamorphosis. Transcript abundance of ghrelin, a putative orexigenic signalling molecule produced in the developing stomach, correlated (p < 0.05) with the emergence of gastric proteolytic activity, suggesting that the stomach’s role in appetite regulation occurs simultaneously with the establishment of proteolytic function. A 3D models series of the GI-tract development indicated a functional pyloric sphincter prior to first feeding. Observations of fed larvae in vivo confirmed that stomach reservoir function was established before metamorphosis, and was thus independent of this event. Mechanical breakdown of food and transportation of chyme through the GI-tract was observed in vivo and resulted from phasic and propagating contractions established well before metamorphosis. The number of contractions in the midgut decreased at metamorphic climax synchronously with establishment of the stomach’s proteolytic capacity and its increased peristaltic activity. Putative osmoregulatory competence of the GI-tract, inferred by abundance of Na+/K+-ATPase α transcripts, was already established at the onset of exogenous feeding and was unmodified by metamorphosis.Conclusions: The functional specialization of the GI-tract was not exclusive to metamorphosis, and its osmoregulatory capacity and reservoir function were established before first feeding. Nonetheless, acid production and the proteolytic capacity of the stomach coincided with metamorphic climax, and also marked the onset of the stomach’s involvement in appetite regulation via ghrelin.Peer Reviewe

Change in nutrient composition of Artemia grown for 3–4 days and effects of feeding on-grown Artemia on performance of Atlantic halibut (Hippoglossus hippoglossus, L.) larvae

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A comparison of growth rate of halibut larvae (Hippoglossus hippoglossus L.) fed wild zooplankton and enriched Artemia

Halibut larvae at an age of 267 day degrees post hatching, were reared through first feeding, outdoors in 100 l plastic bags. There were three feeding regimes: wild zooplankton, Artemia enriched on the algae Isochrysis galbana and Artemia enriched with "Super Selco". The larval growth was very low the first three weeks probably due to low temperature and high larval age at onset of exogenous feeding. At Day 16 the mean myotome height and dry weight were significantly higher for the group fed wild zooplankton, than for the Artemia groups, and the larvae fed Super Selco enriched Artemia had a significant higher myotome height and dry weight than the larvae fed Isochrysis enriched Artemia. There were no significant differences in larval size at Day 23. The low survivals of the two groups fed Artemia, could have been caused by the incomplete digestion of Artemia

Iodine nutrition and toxicity in Atlantic cod (Gadus morhua) larvae

-Copepods as feed promote better growth and development in marine fish larvae than rotifers. However, unlike rotifers, copepods contain several minerals such as iodine (I), at potentially toxic levels. Iodine is an essential trace element and both under and over supply of I can inhibit the production of the I containing thyroid hormones. It is unknown whether marine fish larvae require copepod levels of I or if mechanisms are present that prevent I toxicity. In this study, larval Atlantic cod (Gadus morhua) were fed rotifers enriched to intermediate (26 mg I kg-1 dry weight; MI group) or copepod (129 mg I kg-1 DW; HI group) I levels and compared to cod larvae fed control rotifers (0.6 mg I kg-1 DW). Larval I concentrations were increased by 3 (MI) and 7 (HI) fold compared to controls during the rotifer feeding period. No differences in growth were observed, but the HI diet increased thyroid follicle colloid to epithelium ratios, and affected the essential element concentrations of larvae compared to the other groups. The thyroid follicle morphology in the HI larvae is typical of colloid goitre, a condition resulting from excessive I intake, even though whole body I levels were below those found previously in copepod fed cod larvae. This is the first observation of dietary induced I toxicity in fish, and suggests I toxicity may be determined to a greater extent by bioavailability and nutrient interactions than by total body I concentrations in fish larvae. Rotifers with 0.6 mg I kg-1 DW appeared sufficient to prevent gross signs of I deficiency in cod larvae reared with continuous water exchange, while modelling of cod larvae versus rotifer I levels suggests that optimum I levels in rotifers for cod larvae is 3.5 mg I kg-1 DW

A biotest system for optimalization of environmental parameters for production of halibut fry

A system for controlled testing of different environmental parameters in seawater was made. Both the biotest system and an experimental setup using larvae of the Atlantic Halibut (Hippoglossus hippoglossus L.) are described

Green water in larviculture - An experiment with natural phytoplankton in tanks for first feeding of halibut larvae (Hippoglossus hippoglossus L.)

At 232 day degrees, halibut larvae were transferred from indoor tanks to 1.7 m^3 outdoor tanks for first feeding. The number in each tank was approximately 750. Three tanks were continuously given algal suspension ("green water") and supplied nonenriched Artemia instar II. Six tanks were given filtered deep water ("clear water"). Three of the six were supplied nonenriched Artemia, and three were supplied Artemia prefed in green water. Feeding incidence at day 3 was 47 % in green water and 0 % in clear water. Larval growth was significantly higher in green water compared to clear water, while no significant difference was found between the clear water groups given prefed and nonenriched Artemia. The mean myotome heights for all groups were 0.75 - 0.78 mm at day 7. At day 14 and 21, the mean heights were 1.49 and 1.86 mm in the green water group and 0.84 and 1.05 mm in the clear water groups. The survival rates were also much higher in green water. Out of a total of approximately 2250 halibut larvae in the green water tanks, 684 larvae were found alive at the end of the experiment. Corresponding numbers for the clear water tanks were 57 out of 4500. Preliminary results indicate no nutritional effect of the algae

Effect of water temperature and exposure duration on detachment rate of salmon lice (Lepeophtheirus salmonis); testing the relevant thermal spectrum used for delousing

Thermal delousing has become the most applied method for treatment against salmon lice. However, the temperature range used is strongly aversive for salmonids, and the method is associated with increased mortality. Treatment temperature × duration combinations should be tailored to maximise delousing efficiency and minimize welfare impacts on the host fish. We tested the detachment rate of sessile, pre-adult and adult male and female salmon lice (Lepeophtheirus salmonis) as a function of ambient temperature (11–16 °C), exposure temperature (28–36 °C), and exposure duration (0–120 s). Dead Atlantic salmon (Salmo salar) hosts were used to avoid negative fish welfare and detachment of lice due to fish behaviour. Within the range tested, higher exposure temperatures were associated with higher detachment rates among pre-adult and adult lice, while no sessile lice detached at any temperature. Moreover, no treatment combination detached 100% of lice of any stage, and at 28 °C, detachment of adult females was negligible. Most detachments occurred within the first 30 s of exposure. We conclude that for a given delousing efficiency, lower temperatures must be compensated for by considerably longer exposure durations. This may be a higher risk for the welfare of the host fish than higher temperatures and shorter exposure durations.publishedVersio