No abstract

A total of six isoprotein and isolipid diets for Atlantic salmon, Salmo salar L., were prepared substituting from 0 to 100% of fish meal protein (0–68% of diet by dry weight) with meal from Antarctic krill (Euphausia superba). The feed produced from high inclusion levels of krill meal had lower ability to absorb lipid during vacuum coating than fish meal. Both amino acid and fatty acid compositions of the diets were fairly similar. The experiment commenced using salmon averaging 500 g and ended at a mean weight of 1500–1800 g (140 days of feeding). Moderate amounts of krill meal (20–60% of krill protein) in the diets increased growth during the first 71 days of feeding compared with the fish meal control, while no growth difference was observed during the last 69 days of feeding. This may, at least in parts, be explained by a feed‐attractant function of the krill meal. Muscle dry weight and lipid concentrations were unaffected by the diet. Feed conversion rate increased with high levels of krill meal in the diets (e.g. for the last period from 0.94 in the 0% diet to 1.26 in the 100% diet). This indicates that the fish were able to compensate by eating more to maintain growth. The apparent digestibility coefficients of dry matter and protein were not influenced by diet, but both faecal moisture and lipid had a tendency to increase at the highest inclusion level (all protein from krill meal). This may be related to chitin in the krill diet that is known to decrease lipid absorption and induce diarrhoea (increased water content in faeces). Chitin was not utilized to any major extent. Welfare parameters such as blood haemoglobin, red blood cell counts, plasma protein, cholesterol, triacylglycerols and glucose levels were unaffected by diets. Clinical indicators of cellular damage (alanine aminotransferase and aspartate aminotransferase) were similar indicating no diet‐induced tissue damage during the trial.

No abstract

Planktonic copepods of the genus Calanus play a central role in North Atlantic/Arctic marine food webs. Here, using molecular markers, we redrew the distributional ranges of Calanus species inhabiting the North Atlantic and Arctic Oceans and revealed much wider and more broadly overlapping distributions than previously described. The Arctic shelf species, C. glacialis, dominated the zooplankton assemblage of many Norwegian fjords, where only C. finmarchicus has been reported previously. In these fjords, high occurrences of the Arctic species C. hyperboreus were also found. Molecular markers revealed that the most common method of species identification, prosome length, cannot reliably discriminate the species in Norwegian fjords. Differences in degree of genetic differentiation among fjord populations of the two species suggested that C. glacialis is a more permanent resident of the fjords than C. finmarchicus. We found no evidence of hybridization between the species. Our results indicate a critical need for the wider use of molecular markers to reliably identify and discriminate these morphologically similar copepod species, which serve as important indicators of climate responses.

No abstract

Copepods of the genus Calanus play a key role in marine food webs as consumers of primary producers and as prey for many commercially important marine species. Within the genus, Calanus glacialis and Calanus finmarchicus are considered indicator species for Arctic and Atlantic waters, respectively, and changes in their distributions are frequently used as a tool to track climate change effects in the marine ecosystems of the northern hemisphere. Despite the extensive literature available, discrimination between these two species remains challenging. Using genetically identified individuals, we simultaneously checked the morphological characters in use for C. glacialis and C. finmarchicus identification to compare the results of molecular and morphological identification. We studied the prosome length (1); the antennules and the genital somite pigmentation (2); the morphology of the fifth pair of swimming legs and of the mandible (3). Our results show that none of these morphological criteria can reliably distinguish between C. glacialis and C. finmarchicus. This has severe implications for our current understanding of plankton ecology as a large part of our knowledge of Calanus may be biased due to species misidentification and may subsequently require reinvestigation with the systematic use of molecular tools.

'Atlantic salmon, Salmo salar, utilizes wax ester-rich oil from Calanus finmarchicus effectively' by R. E. Olsen, R. J. Henderson, J. Suotonama, G. AbstractAgainst a background of decreasing availability of fish oils for use in aquaculture, the present study was undertaken to examine whether a wax ester -rich oil derived from the calanoid copepod Calanus finmarchicus, could be used effectively by Atlantic salmon when supplied in their diet. Individually tagged Atlantic salmon of initial weight around 500g were divided into replicate tanks of two dietary groups and fed either a fish oil supplemented diet, or an experimental diet coated with Calanus oil. Wax esters accounted for 37.5% of the lipids in the Calanus oil diet but were absent from the fish oil diet in which triacylglycerols (TAG) were the major lipid class. Over the feeding period (140 days) the salmon fed fish oil displayed a greater increase in length, but there was no significant difference between the two groups in weight gained. The specific growth rates (0.75) and the feed conversion ratio of fish fed the two diets were similar throughout the study.No differences were observed in the apparent digestibility coefficients (ADC) of fish fed Calanus oil or fish oil. The ADC of fatty acids decreased with chain length and increased with unsaturation. Long-chain alcohol utilization showed a similar tendency although there was a notable difference in that saturated long-chain alcohols were utilized better than the comparable fatty acid homologue. In fecal lipid of fish fed Calanus oil, the content of 16:0 alcohol decreased in both the free long-chain alcohol and wax ester fractions, while the corresponding fatty acid increased in the feces of both dietary groups of fish. In contrast, the proportion of the 22:1n-11 alcohol increased in both fecal wax esters and free long-chain alcohol fractions whereas 22:1n-11 fatty acid displayed no accumulation. The observed patterns of fatty acid and long-chain alcohol compositions in fecal lipid compared to those of the initial dietary lipid are consistent with the digestive lipases of salmon preferentially hydrolyzing esters containing PUFA moieties. The wax esters of Calanus oil contained substantial amounts of the n-3 PUFA, 20:5n-3 and 22:6n-3, that were effectively deposited in muscle and liver tissues. No major differences were seen in either lipid content/lipid classes or in gross fatty acid composition of these tissues between the two dietary groups. It is concluded that that Atlantic salmon in seawater can effectively utilize diets in which a major lipid component is derived from zooplankton rich in wax ester without any detrimental change in growth or body lipid composition. This finding gives support to the use of lipid from zooplankton from high latitudes as an alternative or as a supplement to fish oil and a provider of long chain n-3 PUFA in diets for use in salmon aquaculture.

The aim of this study is to examine the reproduction and development of Calanus finmarchicus, C. glacialis and C. hyperboreus in relation to the timing and progress of the phytoplankton spring bloom in different water masses of the Barents Sea. From 1986 to 1988, 8 cruises were conducted, covering Atlantic water in central parts of the Barents Sea and the Polar front region in the north. Dunng the cruises hydrography, nutrients, chlorophyll and abundances of eggs, nauplii and copepodites were mapped. In the Polar front region stabilisation of the water column was caused by ice melting and a surface layer of melt-water. The phytoplankton bloom was initiated in April, more than a month earller than in Atlantic water. A close relationship was found between phytoplankton spring bloonl development and egg production of C. gladalis Egg production of C. finmarchicus did not match the spnng bloom and peaked here dunng the decline of the bloom, probably due to late development of the overwintered stock. Mis-match between egg production and the phytoplankton bloom due to late development may be the main factor m a h n g C. finmarchcus an expatriate in the Arctic. In Atlantic water masses stabhation of the water column was probably caused by formation of a thermocline due to atmospheric warming, and development of the phytoplankton spring bloom was closely related to this process. A strong correlation between rate of egg production and water column chlorophyll content and a high fraction of adult females in the populations before spawning of both C. finmarchicus and C. glacialis indicated a functional relationship between egg production and food supply. C. finmarchicus had a predominantly 1 yr life cycle withln the study area. From copepodite stage distribution the population of C. glacialis was judged to contain individuals having both 1 yr and 2 yr life cycles, and CIV to be a resting stage during winter. The fraction of the population having a life cycle shorter than 2 yr was highest in Atlantic water masses. C. hyperboreus started reproducing before February, showing a pre-bloom spawning strategy. Nauplii older than NIII, which may be the first feeding stage, did not occur in the samples u n t~l the food concentrations increased during the spring bloom. A secondary egg production during the bloom was probably important, and part of the population seemed to have a reproductive strategy similar to that of C. finmarchicus and C. glacialis.