R.D FitzGerald

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.

Stocking density, growth and growth variation in juvenile turbot, Scophthalmus maximus (Rafinesque)

Abstract Although high stocking densities of turbot have been achieved in culture using supplementary oxygenation, this rearing strategy ignores the possibility that high densities may interfere with behavioural interactions between individuals and thereby affect biomass gain. This study describes the effect of stocking density on the growth of juvenile turbot populations. Groups of juvenile turbot were reared at four different densities (initial densities: 0.7, 1.1, 1.5 and 1.8 kg/m 2 ) for 45 days. Treatment density had a significant effect on turbot growth rates over the experimental period. Fish held at the highest density showed lower growth rates and mean weights at the conclusion of the study than fish held at lower densities. The dispersion in fish weights was also affected by stocking density. The variation in fish weights was greatest in the highest density group and as stocking densities increased the growth of some individuals was suppressed. It is concluded that growth of juvenile turbot can be significantly increased and more homogeneous weights achieved by stocking the fish at lower densities than previously reported.

Stability of astaxanthin and canthaxanthin in raw and smoked Atlantic salmon (Salmo salar) during frozen storage

Abstract The objective of the present study was to establish the effect of frozen storage and smoking on the stability of astaxanthin and canthaxanthin in farm raised salmon. Salmon samples were obtained from two sea farms where they had been maintained on commercial feeds containing either astaxanthin or canthaxanthin. The results showed that there was no significant change in visual colour score or carotenoid content of astaxanthin-fed fish during frozen storage for up to 12 weeks. However, smoking fish from this group after frozen storage for 6 and 12 weeks significantly decreased pigment content from an initial level of 9.39 ± 0.23 to 7.99 ± 0.08 and 7.26 ± 0.07 mg kg−1, respectively. Furthermore, Hunter L and a∗ values of raw fish were affected at 6 weeks but not at 12 weeks of storage. Significant changes were measured in canthaxanthin-fed fish stored for up to 12 weeks at −20 °C. Visual colour scores decreased and carotenoid content of the flesh decreased from 10.6 ± 0.27 to 4.36 ± 0.2 mg kg−1. Hunter L values increased, while a∗ values decreased. Smoking canthaxanthin-pigmented fish had no significant effect on the carotenoid content.

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.

Rainbow trout primary epidermal cell proliferation as an indicator of aquatic toxicity: an in vitro/in vivo exposure comparison.

Little or no work has been carried out on primary cell cultures in terms of cellular proliferation and toxicity studies. Cell proliferation represents one of the most relevant cellular functions. Anti-PCNA antibodies have aroused considerable interest recently as potential immunocytochemical markers of proliferation for use in toxicity studies. In this study, PCNA methodology, which was developed primarily for mammalian tissues, was adapted to rainbow trout (Oncorhynchus mykiss (R.)) primary cultured epidermal cells exposed in vivo i.e. whole animal exposures and in vitro for the study of the ecotoxicological potential of the aromatic amine, 2,4-dichloroaniline (2,4-DCA), a member of a little studied and widespread class of aquatic pollutants. There are many approaches to assess the proliferative activity of cells. Immunocytochemical methods offer a high sensitivity and specificity. The immunohistochemical avidin-biotin complex (ABC) method was used for the detection and quantification of PCNA, one of the best-known endogenous proliferation markers, applying the mammalian monoclonal antibody PC-10 to formalin-fixed primary cultures of rainbow trout skin. Here we describe our experience with the immunocytochemical detection and quantification of this proliferation marker. Results indicate that the antibody cross reacts with the corresponding rainbow trout epitope and that the alterations in PCNA labelling in the in vivo and in vitro exposed cultures followed similar patterns. This paper presents data on the validation of rainbow trout primary epidermal culture as an in vitro ecotoxicity model with epidermal proliferation as an endpoint. It can be concluded that cellular proliferation could be used as an indicator of the aquatic toxicity potential of xenobiotics. Correlations between cellular proliferation responses in primary cultures derived from in vivo exposed rainbow trout and primary cultures exposed in vitro were assessed. A dose-response was evidenced in both approaches, however the in vivo exposures appeared to be approximately two orders of magnitude more sensitive than the in vitro exposures. Responses in vitro occurred between 200 and 1000 micro M while in vivo responses were between 2 and 10 micro M. The good qualitative correspondence between the in vitro and in vivo results indicates that studies using trout epidermal cells allow the identification of xenobiotic effects in fish skin. However, further work is required before quantitative predictions i.e. effective concentrations in vivo, can be made from in vitro studies. This study suggests that the in vitro exposed rainbow trout primary cultured cell model with proliferation as an endpoint can be used as an alternative testing procedure to the whole animal assay.

The interrelation of growth and disease resistance of different populations of juvenile Atlantic halibut (Hippoglossus hippoglossus L.)

Abstract Growth of juvenile Atlantic halibut from three areas of the North Atlantic (Canada, Iceland and Norway) was studied in an experiment using individual tagged fish reared at 15°C for 85 days. Fish from each population were subsequently split into two groups and acclimatised to either 12°C or 18°C. The fish were then injected intra-peritoneally with a Vibrio anguillarum bacteria suspension and mortality monitored for 4 weeks. Growth rates of the Canadian population ranked lowest, whereas the Norwegian population had the highest mean growth rates (SGR=1.70% day −1 , 1.62% day −1 and 1.53% day −1 for the Norwegian, Icelandic and Canadian populations, respectively). The halibut from Norway had the best survival following bacterial challenge (80%, 50% and 55% survival for the Norwegian, Icelandic and Canadian populations, respectively). Mortality was higher at 18°C than at 12°C in the Icelandic (62% at 12°C and 27% at 18°C) and Canadian (56% at 12°C and 32% at 18°C) fish, whereas a smaller difference between temperatures was observed in the Norwegian fish (25% at 12°C and 13% at 18°C). Fish that survived the challenge test were those that had grown fastest in the growth trial. Low, but significant, correlations between survival and size and growth were seen, but these correlations varied between populations. In the Canadian population, no correlation between size and growth and survival were seen; only size was correlated ( r =0.27) with survival in the Icelandic population, whereas both size ( r =0.18) and growth ( r =0.17) were correlated with survival in the Norwegian population.

A Novel Method of Microsatellite Genotyping-By-Sequencing Using Individual Combinatorial Barcoding

This study examines the potential of next-generation sequencing based ‘genotyping-by-sequencing’ (GBS) of microsatellite loci for rapid and cost-effective genotyping in large-scale population genetic studies. The recovery of individual genotypes from large sequence pools was achieved by PCR-incorporated combinatorial barcoding using universal primers. Three experimental conditions were employed to explore the possibility of using this approach with existing and novel multiplex marker panels and weighted amplicon mixture. The GBS approach was validated against microsatellite data generated by capillary electrophoresis. GBS allows access to the underlying nucleotide sequences that can reveal homoplasy, even in large datasets and facilitates cross laboratory transfer. GBS of microsatellites, using individual combinatorial barcoding, is potentially faster and cheaper than current microsatellite approaches and offers better and more data.

Comparative composition and shelf-life of fillets of wild and cultured turbot (Scophthalmus maximus) and Atlantic halibut (Hippoglossus hippoglossus)

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 <0.001) levels of α-tocopherol into fillets than turbot. Over 14 days ofstorage on ice, fillets from Atlantic halibut exhibited significantly lower (P =0.020) levels of lipid oxidation than those of turbot. However, malondialdehyde(MDA) concentrations were generally very low, never exceeding 0.6 μgg−1 fillet. Turbot maintained a significantly higher (P< 0.001) pH over the storage period. The lightness (L* values) offillets from both species increased over 14 days of storage, but wassignificantly higher (P < 0.001) in Atlantic halibut than in turbot. Turbotdeveloped a relatively intense yellow colour during storage (decrease in hueangle and increase in b* values), whereas this was not the case forAtlantic halibut. The results of this study demonstrate that fillets of wildAtlantic halibut stored on ice, were less prone to lipid oxidation anddiscolouration than those of wild turbot. However, quality changes in turbotwere very small showing that both fish have tremendous shelf-life capacities interms of lipid oxidation. These findings are considered in the context of knownmaterial for farmed fish.

Embryonic development in ballan wrasse Labrus bergylta

Eight primary embryonic developmental stages were assigned to eggs of ballan wrasse Labrus bergylta using key morphological features following standardized nomenclature: Ia, Ib, II, III, IV, V, VI and VI+, reared from single family clutches under comparable environmental conditions in Ireland and Norway. Development in L. bergylta is typical of demersal marine finfish species with a short egg stage. Hatching occurred c. 123 h post-fertilization (hpf) equivalent to 62·5 degree days at 12·2 ± 1·10° C (mean ±S.D.), after which the larvae swam intermittently near the surface of the water column.

The relationship between individual consumption and growth in juvenile turbot, Scophthalmus maximus

The development of feeding hierarchies was investigated in juvenile turbot, Scophthalmus maximus (Rafinesque) held at two rearing densities for 82 days. Individual biometrics were measured on five occasions and a diet labelled with ballotini glass beads was used in combination with a noninvasive radiographic technique to estimate consumption rates. The results demonstrate that the inclusion of the radio-opaque glass beads in the diet did not significantly reduce consumption by turbot. A significant relationship was found between individual consumption and growth of juvenile turbot. A weight differential within groups increased with time and was largely explained by inter-individual variation in food consumption. This differential was driven by an uneven distribution of food within groups, where individuals of a higher weight than the group average consistently consumed a greater than average share of the group meal, and showed less day to day variation in consumption than their smaller counterparts. The results demonstrate that in captive turbot groups, size hierarchies are mediated, at least in part, through inter-individual differences in food consumption.