E. Schram

The impact of elevated water nitrite concentration on physiology, growth and feed intake of african catfish clarias gariepinus (burchell 1822)

The nitrate threshold concentration in rearing water of African catfish (Clarias gariepinus) was assessed. Female African catfish with an initial mean (SD) weight of 154.3 (7.5) g were exposed to 0.4 (Control), 1.5, 4.2, 9.7 and 27.0 mM nitrate for 42 days. Mean (SD) plasma concentrations of nitrate increased from 71 (29) to 6623 (921) lM at the highest ambient nitrate level. Mean (SD) plasma nitrite concentration ranged from 1.2 (0.5) to 7.9 (9.0) lM. Haematocrit, plasma concentrations of non-esterified fatty acids (NEFA), cortisol, glucose, lactate, osmolality, gill morphology and branchial Na/K-ATPase activity were not affected. Feed intake and specific growth rate were significantly reduced at the highest nitrate concentration. We advise not to exceed a water nitrate concentration of 10 mM (140 mg L 1 NO3-N) to prevent the risk of reduced growth and feed intake in African catfish aquaculture.

Selenium speciation in different organs of African catfish (Clarias gariepinus) enriched through a selenium-enriched garlic based diet

Speciation of Se in fish is needed to elucidate the metabolism of this element in living organisms in the marine environment. In this paper, selenium concentration and its species distribution in several organs and tissues (liver, gills, kidney, muscle and gastrointestinal tract) of African catfish fed with a selenium-enriched garlic based diet was studied. The intention of this paper is focused on both the investigation of selenium distribution in the soluble protein fraction and the detection of selenoaminoacids. Thus, two different procedures have been developed. In the first procedure, screening of selenium in proteins in the Tris-buffer soluble fraction of different tissues was carried out by size exclusion chromatography-inductively coupled plasma-mass spectrometry (SEC-ICP-MS) and by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) after sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) separation and electroblotting onto membranes. For the amino acid analysis, several sample treatments for Se-species extraction, based on enzymatic hydrolysis, were compared. The best results were obtained for incubation at controlled temperature. Application of several sample treatments in conjunction with different chromatographic techniques (reverse phase, anion exchange and ion exchange/size exclusion) was crucial to unambiguous Se-species identification. In Se-enriched African catfish a noticeable increase in the content of selenium in different organs was observed, except for the liver, where the Se level remained unaltered. The kidney was the Se-target organ in animals fed with enriched Se food. Selenomethionine (SeMet) was the main Se species identified in fillet extracts, whereas the presence of selenocysteine (SeCys) was detected in the liver and both SeMet and SeCys were present in the kidney.

Thermal preference of juvenile Dover sole (Solea solea) in relation to thermal acclimation and optimal growth temperature.

Dover sole (Solea solea) is an obligate ectotherm with a natural thermal habitat ranging from approximately 5 to 27°C. Thermal optima for growth lie in the range of 20 to 25°C. More precise information on thermal optima for growth is needed for cost-effective Dover sole aquaculture. The main objective of this study was to determine the optimal growth temperature of juvenile Dover sole (Solea solea) and in addition to test the hypothesis that the final preferendum equals the optimal growth temperature. Temperature preference was measured in a circular preference chamber for Dover sole acclimated to 18, 22 and 28°C. Optimal growth temperature was measured by rearing Dover sole at 19, 22, 25 and 28°C. The optimal growth temperature resulting from this growth experiment was 22.7°C for Dover sole with a size between 30 to 50 g. The temperature preferred by juvenile Dover sole increases with acclimation temperature and exceeds the optimal temperature for growth. A final preferendum could not be detected. Although a confounding effect of behavioural fever on temperature preference could not be entirely excluded, thermal preference and thermal optima for physiological processes seem to be unrelated in Dover sole.

Tailor-made functional seafood for consumers: dietary modulation of selenium and taurine in farmed fish.

Publisher Summary The primary role of a diet is to provide sufficient nutrients to meet the nutritional requirements of an individual. There is an increasing amount of scientific evidence to support the hypothesis that some foods and food components have beneficial health effects beyond the provision of basic nutrients. Scientific and technological developments in the field of food have led to a marked shift in how consumers deal with food and health. There is a growing awareness among consumers that the dietary source and form of food might affect their overall health. The role of food as an agent for improving health has initiated the development of new classes of tailor-made food – functional foods. Functional foods must remain food and must demonstrate their effects from amounts that can normally be consumed in the diet. A functional food can be produced from a food by natural enhancement of the health beneficial components through growing conditions. Addition of the component to the food in order to provide the benefits is another option. The removal of component(s) to reduce any reverse health effect can be regarded as a process for functional foods. Chemical modification of one or several components in the food or changing the bioavailability of its healthy components to improve absorption is another tool to develop functional foods. Natural enhancement of health-beneficial components via the feed during farming is an ideal opportunity to develop new functional foods. This natural enhancement might be better accepted by consumers than addition of the health-beneficial component to the final product.

Welfare interventions in flatfish recirculation aquaculture systems and their economical implications

WELFARE INTERVENTIONS IN FLATFISH RECIRCULATION AQUACULTURE SYSTEMS AND THEIR ECONOMICAL IMPLICATIONS Oliver Schneider a , Edward Schram a , Jeoren Kals a , Jan van der Heul a , Markus Kankainen b & Henk van der Mheen a a IMARES, Yerseke, The Netherlands b Finnish Game and Fisheries Research Institute, Turku Game and Fisheries Research, Turku, Finland Version of record first published: 30 Nov 2012.

Changes in health beneficial components during ice storage of African catfish (Clarias gariepinus).

Ice-storage is the most common method of preserving fresh fish. The aim of this work was to study whether ice storage had an effect on contents at selenium, taurine and fatty acid composition in farmed African catfish (Clarias gariepinus). Gutted fish (n = 40) were stored in melting ice for 21 days, and 5 fish were at regular time intervals randomly drawn from the pool, filleted and freeze-dried. The samples were analyzed for contents of selenium, taurine and fatty acids. During ice storage, water content at fillets increased due to influx of water from melted ice. Only concentrations of water soluble taurine were found to decrease significantly, approximately 25 %, whereas concentration of selenium and the fatty acid profile did not substantially change during storage.