Juha Koskela

Optimal diet composition for European whitefish (Coregonus lavaretus): carbohydrate stress and immune parameter responses

Abstract A feeding trial was conducted on the European whitefish to study the effects of replacing fish meal with fish oil and corn starch on the stress response and immune system parameters. Nine diets with varying levels of fish meal (FM; 38–86%), fish oil (FO; 2–22%) and corn starch (CS; 0–33%), and fixed levels of wheat meal (10%) and vitamin–mineral premix (2%) were formulated and replicates were allocated among 25 tanks following the D-optimality criteria. Fish were fed the extruded diets to satiation for 10 weeks in a flow-through freshwater system at 15 °C. The liver and plasma were sampled at the termination of the trial, and the response surfaces were modeled as Scheffe polynomials specific for mixture designs. Liver glycogen and plasma glucose increased and plasma IgM decreased with increasing CS level. Plasma lysozyme levels decreased with an increase in FM. Plasma cortisol showed a linear response, with the highest values in high-FO, low-CS diets. Mortalities only occurred with high-CS diets. After the feeding trial, the effects of rapid water cooling on stress responses were measured in fish fed either a low-starch diet (66% FM, 22% FO, and 0% CS) or a high-starch diet (53% FM, 2% FO, and 33% CS). Initial plasma samples were collected at 15 °C, whereafter the temperature was reduced to 2 °C in 24 h. Plasma samples were withdrawn, and sampling was repeated after three more days at 2 °C. Cortisol increased from an initial 7 to a peak value of 70 ng ml −1 at the second sampling, and decreased thereafter to 20–30 ng ml −1 . Plasma glucose increased from an initial 3.9 to 4.8 mmol l −1 after 24 h, and further increased to approximately 7.8 mmol l −1 after three more days in cold water. The responses did not differ significantly between fish fed low-starch or high-starch diets. On overall, whitefish showed inadequate adaptation to high dietary carbohydrate levels.

Breeding salmonids for feed efficiency in current fishmeal and future plant-based diet environments

The aquaculture industry is increasingly replacing fishmeal in feeds for carnivorous fish with soybean meal (SBM). This diet change presents a potential for genotype-environment (G × E) interactions. We tested whether current salmonid breeding programmes that evaluate and select within fishmeal diets also improve growth and efficiency on potential future SBM diets. A total of 1680 European whitefish from 70 families were reared with either fishmeal- or SBM-based diets in a split-family design. Individual daily gain (DG), daily feed intake (DFI) and feed efficiency (FE) were recorded. Traits displayed only weak G × E interactions as variances and heritabilities did not differ substantially between the diets, and cross-diet genetic correlations were near unity. In both diets, DFI exhibited moderate heritability and had very high genetic correlation with DG whereas FE had low heritability. Predicted genetic responses demonstrated that selection to increase DG and FE on the fishmeal diet lead to favourable responses on the SBM diet. Selection for FE based on an index including DG and DFI achieved at least double FE gain versus selection on DG alone. Therefore, current breeding programmes are improving the biological ability of salmonids to use novel plant-based diets, and aiding the aquaculture industry to reduce fishmeal use.

Growth, bone mineralization, and heat and low oxygen tolerance in European whitefish (Coregonus lavaretus L.) fed with graded levels of phosphorus

Abstract Trials were conducted to determine the dietary phosphorus (P) requirement of European whitefish, and to assess the effects of sub-optimal P feeding on growth, bone mineralization, lipid accumulation in the body and on heat and low-oxygen tolerance. Four replicate groups of whitefish fingerlings were fed in excess with one of five semipurified diets containing 4.4 to 14.9 g P kg−1. The P requirement was estimated by nonlinear curve fitting to bone mineralization and growth rate data. Dietary P and energy availabilities were measured at the determined requirement level. Fish fed no P supplement showed typical hypophosphatemia in poorly mineralized bones, a low whole-body P content and a low plasma phosphate concentration. Hypophosphatemic fish grew slower and had elevated whole body lipid concentrations. To obtain 95% of the maximum vertebra ash concentration and maximum growth, respectively, 6.5- and 6.2-g available P kg−1 diet was required. Fish fed low dietary P contents had higher whole body lipid levels than fish fed P at or above the determined requirement level. Hypophosphatemic fish had slightly, although statistically significant, lower upper lethal temperature than fish fed with adequate P contents (28.8 vs. 29.4 °C). Tolerance of low dissolved oxygen did not differ between fish fed low or high P contents (1.47 vs. 1.45 mg l−1).

Optimal diet composition for European whitefish (Coregonus lavaretus): analysis of growth and nutrient utilisation in mixture model trials

Abstract Two feed mixture trials were conducted on the European whitefish. For both trials, nine diets with varying levels of fish meal (FM), fish oil (FO) and cornstarch (CS), and fixed levels of wheat meal and vitamin–mineral premix (12%), were formulated according to d -optimality criteria assuming a quadratic response surface. In the two trials, the proportions of the ingredients were, respectively: 38–86% and 43–85% for FM, 2–22% and 0–30% for FO, and 0–33% and 0–15% for CS. The extruded diets were fed to satiation for 72 and 85 days in a flow-through, freshwater system at 15 °C. Optimal allocation of replicates among 25 and 29 tanks was based on d -optimality criteria. The response surfaces were modelled as quadratic and super-cubic polynomials specific for mixture designs. The data from the trials were combined for the final analysis, which included the experiment as a random effect. Fish growth increased with increasing FM content up to 66.3% FM (16.7% FO and 5.0% CS). Protein growth peaked at a somewhat higher FM content of 72.0% (10.2% FO, 5.9% CS), and lipid deposition rate at the highest studied FO content (53.1% FM, 30.0% FO and 4.9% CS). Feed efficiency improved with decreasing CS content and the highest value was obtained with the mixture containing 58.0% FM, 30.0% FO and 0.0% CS. Protein retention efficiency was improved with decreasing FM content and peaked at a mixture of 50.2% FM, 30.0% FO and 7.8% CS. The diet inducing 95% of the maximum growth with the minimum FM content comprised of 51.2% FM, 30.0% FO and 6.8% CS. Based on the data from these two experiments, an area of optimal diet formulation can be assessed by graphically superimposing isobars of 95% growth, feed efficiency and dietary protein utilisation responses. This optimal composition for the European whitefish appears to be in the range of 53–61% FM, 24–30% FO and 0–7% CS together with the 12% wheat meal and vitamin–mineral premix. However, this optimisation is based on round weight and because high dietary lipid levels induced high lipid deposition rates, the practical optimum for dressed weight would be at a somewhat lower FO level. Mixture experimentation proved to be an efficient method to rapidly screen European whitefish diets for nutritional optimisation.

Quality and production trait genetics of farmed European whitefish, Coregonus lavaretus.

We present here phenotypic and genetic parameters for the major quality and production traits of farmed European whitefish. A total of 70 families were produced by mating each of 45 sires to an average of 1.6 dams and each of the 52 dams to an average of 1.3 sires. A total of 2,100 individuals were recorded for survival, and 507 individuals for growth and quality-related traits. The 4 major results were as follows: first, all traits exhibited nonzero heritabilities except for fillet gaping and fillet protein%. The heritabilities for the production traits were harvest weight (0.42 ± 0.10), gutted weight (0.40 ± 0.10), fillet weight (0.36 ± 0.09), maturity score (0.27 ± 0.11, on liability scale), survival (0.19 ± 0.05, on liability scale), carcass% (0.14 ± 0.07), and fillet% (0.11 ± 0.06). The heritabilities for the quality traits were condition factor (0.49 ± 0.10), fillet lipid% (0.37 ± 0.10), muscle texture (0.30 ± 0.09), Distell lipid reading (0.26 ± 0.09), fillet lightness (0.16 ± 0.07), fillet gaping (0.04 ± 0.06), and fillet protein% (0.04 ± 0.06). Second, the quality traits that were significantly genetically correlated with each other were all related to lipid deposition. Increasing fillet lipid% (an undesired change in whitefish) was genetically related to desired lighter fillet color [genetic correlation (r(G)) = 0.70 ± 0.22] and to undesired greater condition factor (0.39 ± 0.17). None of the other genetic correlations between condition factor, fillet lipid%, muscle texture, fillet lightness, fillet gaping, and fillet protein% were significant. Third, BW and gutted weight were genetically related to the quality traits that were genetically related to lipid deposition. Increasing harvest weight was genetically related to high fillet lipid% (r(G) = 0.59 ± 0.14), lighter fillet color (0.61 ± 0.25), and to greater condition factor (0.60 ± 0.12). All other genetic correlations of harvest weights with the quality traits were nonsignificant, indicating that rapid growth was not genetically related to gaping and softer flesh. Fourth, none of the genetic correlations of carcass%, fillet%, maturity, and survival with the quality traits were significant, implying weak genetic integration between the traits. Yet, marginally significant genetic correlations were found for fillet lipid% with maturity score (r(G) = -0.46 ± 0.24) and survival (0.36 ± 0.19). These results provide the genetic basis for assessing the potential to improve product quality via selective breeding.

Genetic potential for the regulation of variability in body lipid and protein content of European whitefish ( Coregonus lavaretus )

Animals may have target levels for lipid and protein stores which they try to maintain by feedback mechanisms. Thus, variation in initial body composition may be related to subsequent feed utilisation, for animals to maintain body composition in homeostasis. We assessed whether such relationships are genetically determined within a farmed population of European whitefish (Coregonus lavaretus) grown either on fishmeal or soyabean-meal diets. Soyabean meal is an increasingly-used ingredient in aquaculture feeds. Fish from thirty-five paternal families were analysed for initial body lipid and protein content, and for subsequent daily weight gain, daily feed intake, feed efficiency and their lipid and protein components. The results showed that none of the correlations of initial body lipid percentage with subsequent growth and feed utilisation were statistically significant. In contrast, low initial protein percentage was related to increased subsequent weight gain, protein gain and protein retention efficiency. This led to reversed ranking of families during growth for body protein percentage. Thus, mechanisms maintaining stable body lipid percentage across the population were weak, whereas the mechanisms stabilising body protein percentage were strong and successful. This explains the observations that cascades of lipid deposition occur during fish growth, leading to high amounts of phenotypic and genetic variation for percentage body lipid. In contrast, protein percentage remains phenotypically and genetically more invariable, reducing the potential for selective breeding. The soyabean-meal diet, in turn, induced only weak genotype x diet interactions, aiding in the genetic improvement of farmed fish to adapt to future feeds.

Economic values of supply chain productivity and quality traits calculated for a farmed European whitefish breeding program

ABSTRACT Economic values of different fish traits are needed to direct breeding programs to optimize economic benefits for aquaculture industry. The aim of this article is to highlight and calculate how different traits affect the value of farmed fish supply chain. Supply chain approach is needed to calculate economic impact of fish traits because several fish traits affect costs and returns not only in fish farming but also at the processing and retail level. In this article, economic values are calculated for 14 productivity and product quality traits in European whitefish (Coregonus lavaretus). Productivity affecting traits, such as growth, mortality and different yields, are included in the study. In addition, economic values are calculated for several quality traits like fillet gaping, appearance and fat content of flesh. Productivity traits had the highest economic importance if the traits could be improved. However, quality traits may cause even higher economic losses, if the quality decreases. Thus, the management of the breeding program should pay simultaneous attention to both quality and productivity traits.