Nutritional composition of rotifers following a change in diet from yeast and emulsified oil to microalgae

Rotifers, Brachionus plicatilis, fed baker's yeast and a lipid emulsion (High DNA Super Selco, INVE Aquaculture NV Systems SA, Belgium), were harvested and fed Isochrysis galbana for 72 h, the nutrient composition was analysed during this period. The enrichment effect on the rotifers following transfer to I. galbana was most pronounced for ascorbic acid and thiamin. I. galbana seemed to contribute very little as a source of the lipid-soluble vitamins. Most of the minerals and trace elements were unaffected by the transfer to I. galbana, but Fe, Mn, As and Cd increased, Cu and Ni decreased whereas the effect on Cr and Mo were uncertain. The fatty acid composition of the rotifers changed towards the composition of I. galbana during the experimental period. Intermediate glycogen levels were measured in the rotifers at all sampling times. With the exception of lysine, serine and proline, all amino acid levels seemed to be unaffected by the transfer to I. galbana. This study showed that transfer of rotifers to microalgae (I. galbana) feeding had a positive effect on nutritional value. Macronutrients were maintained at adequate levels, and algal feeding improved the nutritional quality of rotifers with respect to water-soluble vitamins. Changes in rotifer nutrient composition are discussed in relation to nutritional requirements of fish larvae.     

Effect of fish meal quality on growth of juvenile wolffish, Anarhichas lupus L.

The objective of the present study was to evaluate the effect of fish meal quality on growth, feed conversion and protein utilization in common wolffish. Anarhichas lupus L. The study involved comparison between low-temperature-processed (Norse-LT) and regular fish meal (NorSeaMink) included in dry pellets. Results obtained for these dry feeds were compared with those obtained using moist feed containing squid mantle. The results show better growth rate, feed conversion factor, protein efficiency rate, (PER) and productive protein values (PPVs), when using low-temperature-processed meals compared with regular fish meals in feed to wolffish. No specific differences were found in growth rate and feed conversion factor between fish fed diets containing low-temperature-processed meal or squid mantle. Whole body lipid content was highly influenced by dietary content. No effect of dietary moisture content was demonstrated in this study.     

Chemical and sensory quantification of geosmin and 2-methylisoborneol in rainbow trout (Oncorhynchus mykiss) from recirculated aquacultures in relation to concentrations in basin water

Globally, aquaculture systems with water recirculation experience increasing problems with microbial taste and odor compounds (TOCs) such as geosmin and 2-methylisoborneol (MIB). This study investigated the content of geosmin and MIB in water and the flesh of 200 rainbow trouts from eight recirculated aquaculture systems in Denmark. TOC content in the fish flesh was measured by a dynamic headspace extraction method and was evaluated by a sensory panel. The results showed significant correlations between TOC content in water and fish and between chemical analysis and sensory perception. When geosmin exceeded 20 ng/L in the water, 96% of the fish had an intense muddy flavor, but below 10 ng geosmin/L, 18% of the fish (only 3% in special depuration ponds) had an intense muddy flavor. The results indicate that TOC levels <10 ng/L will ensure that a negligible portion of the fish obtains an unpalatable taste and flavor due to TOCs.     

Temperature modulates liver lipid accumulation in Atlantic salmon (Salmo salar L.) fed low dietary levels of long‐chain n‐3 fatty acids

Atlantic salmon (Salmo salar) were fed five graded levels of eicosapentaenoic acid (EPA, 20:5n‐3) and docosahexaenoic acid (DHA, 22:6n‐3), from 1.4 to 5.2% of total fatty acids (FA, 5–17 mg kg^?1 feed), and grew from ~160 g to ~3000 g, with the period from 1450 g onwards conducted both at 6 °C and at 12 °C. All fish appeared healthy, and there were no diet‐related differences in haematological or plasma parameters, as well as intestinal histological or gut microbiota analysis. Fish reared at 6 °C had higher accumulation of storage lipids in the liver compared to fish reared at 12 °C. Liver lipids also increased with decreasing dietary EPA + DHA at 6 °C, while there was no such relationship at 12 °C. Gene expression of SREBP1 and 2, LXR, FAS and CPT1 could not explain the differences in liver lipid accumulation. In liver polar lipids, DHA was found to be reduced when dietary EPA + DHA was <2.7% of FAs, while the level of EPA in the membranes was not affected. In conclusion, reducing dietary EPA + DHA from 5.2 to 1.4% of total FAs had a minor impact on fish health. Temperature was the factor that most affected the liver lipid accumulation, but there was also an interaction with dietary components.     

Correction to: Population genetic structure of lumpfish along the Norwegian coast: aquaculture implications

The original version of this article unfortunately contained an error where the figure caption for Figures 3 and 4 was mixed.     

渔业统计——渔业管理者和科学家的一个重要工具

FISHERIES STATISTICS： AN IMPORTANT TOOL FOR MANAGERS AND SCIENTISTS This presentation focuses on the type of information collected through fisheries statistics that could be useful to scientists and fisheries managers. In Norway the use of fisheries statistics as an analyzing tool for marine scientists can be dated back to around 1973. At that time the Directorate of Fisheries started to computerize information from logbooks of the trawl fleet. The fisheries managers started to use fisheries statistics as an analyzing tool by the late 1970's. Once again the computerization of sales notes information together with additional statistical information, enabled the manager to regroup the information according to new problems to be analyzed and new questions to be answered.     

Histological alterations in the liver of sea bream, Sparus aurata L., caused by short- or long-term feeding with vegetable oils. Recovery of normal morphology after feeding fish oil as the sole lipid source

This study evaluated the effects of fish oil (FO) replacement by vegetable oils [soybean oil (SO), rapeseed oil (RO), linseed oil (LO)] and subsequent feeding with FO on the liver morphology of sea bream. A short-term trial (3 months) and long-term trial (6 months) were carried out feeding sea bream with the following experimental diets: FO100%; SO60% + FO40%; RO60% +FO40%; LO60% + FO40%; SO + RO +LO60% + FO40%. Finally, all groups from the long-term trial were fed with FO100% for 95 days (washout period). Liver samples were taken for histological and biochemical studies. In both the short- and long-term trials, livers of sea bream fed LO60% and SO + RO + LO60% showed a similar hepatic morphology to that observed in fish fed FO100%. In contrast, sea bream fed SO60% showed an intense steatosis, with foci of swollen hepatocytes containing numerous lipid vacuoles. After the washout period, a considerable reduction of the cytoplasmic vacuolation and the lipid vacuole accumulation were observed in the livers of fish fed the different experimental diets. The results of this study suggested that the type of non-essential fatty acid, characteristic of vegetable oils, induces the appearance of steatosis in the following order: linoleic acid > linolenic acid > oleic acid. However, the liver alterations found during the experimental periods with vegetable oils are reversible when the fish are re-fed with a balanced diet (FO100%), indicating the non-pathological character of these histological changes.     

Effect of feed composition and feeding frequency on growth, feed utilization and nutrient retention in juvenile Atlantic cod, Gadus morhua L.

Juvenile Atlantic cod (Gadus morhua) were fed extruded feeds formulated to contain 360–660 g kg^?1 protein, 80–280 g kg^?1 lipid and 80–180 g kg^?1 starch at feeding frequencies of either once per day or every second day to satiation. The trial was conducted at 8 °C and lasted for 28 weeks during which fish were weighed five times at regular intervals. Sampling for proximate analysis was performed at the start, after 12 weeks and at the end of the trial. Fish grew from an average weight of 192 g to between 750 and 866 g, with growth being negatively affected by low dietary protein concentration. High dietary starch concentrations had some negative effects on growth, whereas changes in dietary fat concentration had no significant effect on growth. Liver indices (at the end of the experiment) varied between 80 and 170 g kg^?1, and there was a negative correlation between the ratio of protein to fat and liver index. Feed conversion ratio (FCR) ranged between 0.74 and 0.88, and feed utilization improved with increasing concentrations of dietary protein and fat. Increasing dietary starch concentrations resulted in poorer feed utilization. To achieve good growth and protein retention, and avoid excessive liver size in juvenile cod, feeds should contain 500–600 g kg^?1 crude protein, 130–200 g kg^?1 lipid and <150 g kg^?1 starch.     

Dietary lipid sources for seabream and seabass: growth performance, tissue composition and flesh quality

Due to its traditionally good availability, digestibility and high content of n ? 3 HUFA, fish oil is the main lipid source in fish feeds. However, world demand for this product has grown significantly in recent years, whereas its production, based on fisheries landings, is static. The purpose of the present study was to assess the effect of partial replacement of fish oil in compound diets for gilthead seabream and seabass, by several vegetable oil sources, on growth, dietary fatty acid utilization and flesh quality. Five iso‐energetic and isoproteic experimental diets were formulated (25% lipid content). Fish oil was the only added lipid source in the control (FO) diet, and it was included in the other experimental diets at a level high enough (40% of FO diet) to keep the n ? 3 HUFA levels well over 3% in order to cover the essential fatty acid requirements of these species. Fish oil was replaced by soyabean oil (SO), rapeseed oil (RO) and linseed oil (LO) or a mixture (Mix) of them. Feed intake in all dietary groups was in the range of results obtained for commercial diets in both species, and growth and feed utilization were very good. The results show that, providing a minimum content of essential fatty acids in the diet, it is possible to replace up to 60% of the fish oil by SO, LO and RO or a mixture of them in diets for seabream and seabass, without compromising fish growth. Fatty acid composition of liver and muscle reflected that of the diet, but utilization of dietary lipids differed between these two tissues and was also different for the different fatty acids. Despite reduction in dietary saturated fatty acids by the inclusion of vegetable oils, their levels in fish liver were as high as in fish fed the fish oil diet, whereas, in muscle, levels were reduced according to that in the diet. Linoleic and linolenic acids were accumulated in the liver proportionally to their levels in the diet, suggesting a lower oxidation of these fatty acids in comparison to other 18C fatty acids. Regarding eicosapentaenoic acid (20 : 5n ? 3; EPA), docosahexaenoic acid (22 : 6n ? 3; DHA) and arachidonic acid (20 : 4n ? 6; ARA), these essential fatty acids were reduced in the liver at a similar rate, whereas DHA was preferentially retained in the muscle in comparison with the other fatty acids, denoting a higher oxidation particularly of EPA, in the muscle. Some other PUFA increased despite their low dietary levels in seabream fed LO diets and in seabass fed SO diet, suggesting the stimulation of delta‐6 and delta‐5 desaturase activity in marine fish. Despite differences in fatty acid composition, fillet of fish fed vegetable oils was very well accepted by trained judges when assessed cooked.