Conditions fish encounter during embryogenesis and early life history can leave lasting effects not only on morphology, but also on growth rate, life-history and behavioural traits. The ecology of offspring can be affected by conditions experienced by their parents and mother in particular. This review summarizes such early impacts and their ecological influences for a variety of teleost species, but with special reference to salmonids. Growth and adult body size, sex ratio, egg size, lifespan and tendency to migrate can all be affected by early influences. Mechanisms behind such phenotypically plastic impacts are not well known, but epigenetic change appears to be one central mechanism. The thermal regime during development and incubation is particularly important, but also early food consumption and intraspecific density can all be responsible for later life-history variation. For behavioural traits, early experiences with effects on brain, sensory development and cognition appear essential. This may also influence boldness and other social behaviours such as mate choice. At the end of the review, several issues and questions for future studies are given.

Early environment influences later performance in fishes.

Towards a classification and an understanding of developmental relationships of vertebral body malformations in Atlantic salmon (Salmo salar L.).

A semantic model for overall welfare assessment of Atlantic salmon reared in sea cages is presented. The model, called SWIM 1.0, is designed to enable fish farmers to make a formal and standardized assessment of fish welfare using a set of selected welfare indicators. In order to cover all welfare relevant aspects from the animals’ point of view and to create a science-based tool we first identified the known welfare needs of Atlantic salmon in sea cages and searched the literature for feasible welfare indicators. The framework of semantic modelling was used to perform a structured literature review and an evaluation of each indicator. The selected indicators were water temperature, salinity, oxygen saturation, water current, stocking density, lighting, disturbance, daily mortality rate, appetite, sea lice infestation ratio, condition factor, emaciation state, vertebral deformation, maturation stage, smoltification state, fin condition and skin condition. Selection criteria for the indicators were that they should be practical and measureable on the farm, that each indicator could be divided into levels from good to poor welfare backed up by relevant scientific literature. To estimate each indicator’s relative impact on welfare, all the indicators were weighted based on their respective literature reviews and according to weighting factors defined as part of the semantic modelling framework. This was ultimately amalgamated into an overall model that calculates welfare indexes for salmon in sea cages. More importantly, the model identifies how each indicator contributes (negatively and positively) to the overall index and hence which welfare needs are compromised or fulfilled.

Salmon Welfare Index Model (SWIM 1.0): a semantic model for overall welfare assessment of caged Atlantic salmon: review of the selected welfare indicators and model presentation

Improving feed efficiency (FE) is key to reducing production costs in aquaculture and to achieving sustainability for the aquaculture industry. Feed costs account for 30–70% of total production costs in aquaculture; much work has been done on nutritional and husbandry approaches to improve FE but only a limited amount of research has been devoted to using genetics, despite its potential. This paper reviews past work to improve FE in fish using selective breeding and assess future directions. Direct selection on FE traits requires methods to measure individual feed consumption and estimate FE efficiently and accurately. This is particularly difficult to do in fish because of the environment in which they live. Many of the published studies on FE were found to be inaccurate because of methodological problems. The relatively low heritability estimates of FE traits in fish published to date are probably partly as a result of inaccurate measurements of feed intake. Improving ways to measure the individual feed intake with high accuracy will be critical to the successful application of genetics to improving FE. Indirect selection criteria that could be used to improve FE (including growth after starvation/refeeding, body composition, neuropeptides or hormone levels) are discussed. Promising approaches to measuring feed intake accurately that may enable these studies to be undertaken are identified. More work using these will be needed prior to assessing the practicality of the introduction of direct or indirect traits for FE in fish genetic improvement programmes.

/pdf/improving-feed-efficiency-in-fish-using-selective-breeding-a-2vjx8r2glf.pdf

Improving feed efficiency in fish using selective breeding: A review

Fish store large quantities of vitamin D in their liver and fat tissues, including the fat associated with muscle, and this makes fish an important dietary source of vitamin D. Fish do not synthesize vitamin D and are fully dependent on dietary sources to meet their requirement. Under natural circumstances planktonic vitamin D accumulates in the aquatic food chain. In aquaculture, formulated diets are used and vitamin D intake can be manipulated. The minimum dietary requirement for vitamin D has been established in several fish species. The role of vitamin D in fish physiology is still enigmatic. Till the 1970s there was consensus that fish accumulate but not metabolize vitamin D. There is substantial evidence now, four decades later, that fish have a vitamin D endocrine system with similar functions as in mammals. We here summarize the major characteristics of the fish vitamin D endocrine system. The hydroxylation of vitamin D to more polar metabolites, their plasma levels and protein-bound transport in blood plasma will be discussed. The vitamin D receptor profile, receptor distribution and responses to vitamin D are reviewed for the key target tissues (gill, intestine, kidney and bone). We will address the classical slower actions through transcription factors as well as the faster G-protein coupled (membrane) receptor mediated effects. We then review the dietary requirement of vitamin D in aquaculture and address some lesser known functions of the vitamin D endocrine system.

The significance of vitamin D for fish: a review.

The expressions of trypsin and chymotrypsin in the pyloric caeca of Atlantic salmon (Salmo salar L.) were studied in three experiments. Two internal (trypsin phenotypes, life stages) and three common external factors (starvation, feeding, temperatures) influencing growth rates were varied. Growth was stimulated by increased temperature and higher feeding rate, and it was depressed during starvation. The interaction between trypsin phenotype and start-feeding temperature affected specific activity of trypsin, but not of chymotrypsin. Trypsin specific activity and the activity ratio of trypsin to chymotrypsin (T/C ratio) increased when growth was promoted. Chymotrypsin specific activity, on the other hand, increased when there was a reduction in growth rate whereas fish with higher growth had higher chymotrypsin specific activity resulting in lower T/C ratio value. During a rapid growth phase, trypsin specific activity did not correlate with chymotrypsin specific activity. On the other hand, a relationship between specific activities of trypsin and chymotrypsin could be observed when growth declined, such as during food deprivation. Trypsin is the sensitive key protease under conditions favouring growth and genetically and environmentally affected, while chymotrypsin plays a major role when growth is limited or depressed. Trypsin specific activity and the T/C ratio value are shown to be important factors in the digestion process affecting growth rate, and could be applicable as indicators for growth studies of fish in captive cultures and in the wild, especially when food consumption rate cannot be measured.

/pdf/different-expressions-of-trypsin-and-chymotrypsin-in-o247johx77.pdf

Different expressions of trypsin and chymotrypsin in relation to growth in Atlantic salmon (Salmo salar L.)

An earlier study demonstrated that under-yearling (0+) Atlantic salmon (Salmo salar L.) smolt had a lower vertebral mineral content and mechanical strength and higher prevalence of vertebral deformities than 1+ smolt during the early seawater (SW) phase. The present study aimed to examine if commercial extruded high-energy diets need to be supplemented additional minerals for proper bone mineralization and prevention of bone deformities in fast growing 0 +  smolts. We studied vertebral morphology with radiology, and bone mineral content and mechanical strength in 60 g 0+ smolt fed diets with a normal (NM) or elevated (HM) bone mineral (P and Ca) contents from SW transfer (week 0) until 10 times weight increase at week 17. Thereafter, both groups were fed a commercial diet until a mean slaughter weight of 4100 g after 57 week. There were no differences in body weight and length between the dietary groups during the study, while the condition factor differed significantly at the final sampling (NM 1.40; HM 1.29). The most common bone deformity observed was compressions in the tail region of the vertebral column. Lower incidences of vertebral deformities (percent individuals with one or more deformed vertebrae) was observed in the HM group in week 17 (HM 20%; NM 47%) and week 57 (HM 37%; NM 73%), also reflected by higher vertebral length/dorso-ventral diameter ratio in weeks 17 (HM 0.99; MN 0.92) and 57 (HM 0.97; NM 0.88). The HM group had significantly higher vertebral mineral content (HM 550 g kg−1; NM 480 g kg−1) and mechanical strength (HM 9050 g mm−1; NM 4600 g mm−1) than the NM group after 8 week feeding. Plasma levels of Ca, P and D-vitamin metabolites recorded in week 8 reflected changes in P homeostasis, but could not explain the preventive effect of the HM diet on development of bone deformities. The results suggest that elevated dietary mineral content during the early SW phase may reduce the prevalence of vertebral deformities in fast growing 0 +  salmon smolts.

Supplementation of dietary minerals during the early seawater phase increase vertebral strength and reduce the prevalence of vertebral deformities in fast‐growing under‐yearling Atlantic salmon (Salmo salar L.) smolt

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Different expressions of trypsin and chymotrypsin in relation to growth in Atlantic salmon (Salmo salar L.)

Supplementation of dietary minerals during the early seawater phase increase vertebral strength and reduce the prevalence of vertebral deformities in fast‐growing under‐yearling Atlantic salmon (Salmo salar L.) smolt