Ivar Lund

Genetic variation for growth rate, feed conversion efficiency, and disease resistance exists within a farmed population of rainbow trout

Abstract The objective of this study was to test that additive genetic (co)variation for survival, growth rate, feed conversion efficiency, and resistance to viral haemorrhagic septicaemia (VHS) exists within a farmed population of rainbow trout. Thirty sires and 30 dams were mated by a partly factorial mating design. Each sire was mated to two dams, and each dam was mated to two sires, producing 50 viable full-sib families (29 sires, 25 dams). The fish from these families were reared for a 215-day growout period, and were assessed for survival between days 52 and 215, growth rate (i.e., body weight on days 52, 76, 96, 123, 157, 185, and 215, and body length on days 52 and 215); feed conversion efficiency between days 52–215, 52–76, 77–96, 97–123, 124–157, 158–185, and 186–215, and VHS resistance. REML estimates of additive genetic variation for the body weights, body lengths, and feed conversion efficiencies were obtained by fitting univariate linear (reduced) animal models. Additive genetic variation for VHS resistance was estimated by fitting a Weibull, sire–dam frailty model to time until death of fish challenged with VHS. Genetic correlations were estimated among the body weights, body length, and feed conversion efficiencies that expressed additive genetic variation, while genetic correlations between VHS resistance and the body weights, body length, and feed conversion efficiencies were approximated as product–moment correlations among predicted breeding values of the sires and dams. Additive genetic variation was found to be very low for survival, body weight on days 52 and 76, body length on day 52, and feed conversion efficiency between days 185 and 215. However, additive genetic variation was detected for body weight on days 96, 123, 157, 185, and 215 [coefficient of additive genetic variation (CV)=8.4–28.4%, heritability (h2)=0.35 for body weight on day 215], body length on day 215 (CV=6.9%, h2=0.53), feed conversion efficiency between days 52–215, 52–76, 77–96, 97–123, 124–157, and 158–185 (CV=4.0–13.9%), and VHS resistance (additive genetic variance for log-frailty=0.24, h2 on the logarithmic-time scale=0.13). Genetic correlations among the body weights, body length, and feed conversion efficiencies that expressed additive genetic variation were generally favourable and moderate-to-very strong (0.55–0.99), though there were unfavourable correlations (−0.01 to −0.33) between the predicted breeding values for VHS resistance and the predicted breeding values for the body weights, body length, and feed conversion efficiencies. These results demonstrate that additive genetic (co)variation for growth rate, feed conversion efficiency, and VHS resistance does exist within the farmed population of rainbow trout, and indicates that selective breeding for these traits can be successful.

Dietary supplementation of essential fatty acids in larval pikeperch (Sander lucioperca); short and long term effects on stress tolerance and metabolic physiology.

The present study examined the effects of feeding pike perch larvae Artemia, enriched with either docosahexanoic acid (DHA), arachidonic acid (ARA), oleic acid (OA), olive oil (OO) or a commercial enrichment DHA Selco (DS) on tissue lipid deposition, stress tolerance, growth and development, and metabolic rate. There was higher tissue retention of ARA than DHA at comparable inclusion levels. No differences were observed between diets on the percentage contribution of ARA or DHA to the fatty acid profile of tissues (head and trunk). Total fatty acid content (mgg(-1)) was significantly higher in the head, reflecting its high content of neural tissue. Observations on larval erratic behaviour and mortality following exposure to salinity stress suggested that high inclusions levels of DHA had an alleviating effect, while ARA did not. Particularly larval groups reared for 16 days on diets enriched with OO and OA had mortality rates approaching 100% within two hours. Interestingly, this tendency, although not as pronounced, was also apparent in juvenile fish after 120 days of rearing on a common diet. Standard metabolic rate in larvae on an OO enriched diet was significantly elevated, but otherwise no groups had significant changes to their respiratory physiology. In addition to increased stress challenge sensitivity, early feeding with OA had long term impact on pike perch neural development indicated by a smaller brain size in juvenile fish. In conclusion, lack of DHA in the diet of pikeperch larvae suggests that this long chain polyunsaturated fatty acid is involved in processes that increase stress tolerance and that lack of dietary DHA in early larval stage caused increased stress sensitivity and long-term impaired neural development, while it does not appear to affect metabolic rate at rest.

Humoral and mucosal defense molecules rhythmically oscillate during a light-dark cycle in permit, Trachinotus falcatus.

Circadian rhythm provides organisms with an internal system to maintain temporal order in a dynamic environment. This is typified by a 24-h cycle for a number of physiological processes, including immunity. The present study characterized the humoral and mucosal defense molecules and their dynamics during a light-dark (LD) cycle in juvenile permit, Trachinotus falcatus. All studied defense molecules were constitutively identified in serum and skin mucus. Serum generally exhibited higher levels of these defenses than skin mucus, with the exception of anti-protease (ANTIPRO). The difference in ANTIPRO, lysozyme (LYZ), esterase (ESA) and catalase (CAT) levels between serum and skin mucus was not affected by the phase of the daily cycle. However, a clear phase-dependent difference was observed in protease (PRO), globulin (GLOB), myeloperoxidase (MPO), alkaline phosphatase (ALP) and glutathione peroxidase (GPX) levels. Activities of ALP and GPX displayed significant daily rhythmicity in both serum and skin mucus. Circadian profile of ALP was identical in both biofluids, but an antiphasic feature was exhibited by GPX. GLOB and MPO levels also exhibited significant daily oscillation but only in serum with acrophases registered at ZT 14.5 and 6.15, respectively. Mucus PRO and serum ANTIPRO demonstrated significant temporal variations during a daily cycle albeit not rhythmic. Cluster analysis of the defense molecules in serum and skin mucus revealed two different daily profiles suggesting a possibility of distinct circadian control between humoral and mucosal immunity. These observations indicate that LD cycle had a remarkable impact in the defense molecules characterizing the humoral and mucosal immunity in permit. Daily rhythmic patterns of these defense molecules contribute to our understanding of the barely explored interplay of immunity and circadian rhythm in teleost fish. Lastly, the results could be useful in developing aquaculture practices aiming at modifying the immune functions of permit for improved health.

Influence of Dietary Lipid and Protein Sources on the Sensory Quality of Organic Rainbow Trout (Oncorhynchus mykiss) After Ice Storage

The influence of dietary protein and lipid sources on the quality of organic rainbow trout (Oncorhynchus mykiss) was studied. The protein and oil sources were fishmeal, fish oil, and organic vegetable protein and oils. Sensory profiling was performed during 3 to 14 days of ice storage along with lipid analyses of the fillet. Overall, the results showed that the sensory characteristics of the trout were affected in different ways during ice storage. The source of lipid seemed to affect the sensory quality at the beginning of the storage period, while the protein source seemed to have a more pronounced impact at the end of the storage period.

Effects of organic plant oils and role of oxidation on nutrient utilization in juvenile rainbow trout (Oncorhynchus mykiss)

Producing organic fish diets requires that the use of both fishmeal and fish oil (FO) be minimized and replaced by sustainable, organic sources. The purpose of the present study was to replace FO with organic oils and evaluate the effects on feed intake, feed conversion ratio (FCR), daily specific growth rate (SGR) and nutrient digestibility in diets in which fishmeal protein was partly substituted by organic plant protein concentrates. It is prohibited to add antioxidants to organic oils, and therefore the effects of force-oxidizing the oils (including FO) on feed intake and nutrient digestibility was furthermore examined. Four organic oils with either a relatively high or low content of polyunsaturated fatty acids were considered: linseed oil, rapeseed oil, sunflower oil and grapeseed oil. Substituting FO with organic oils did not affect feed intake (P > 0.05), FCR or SGR (P > 0.05) despite very different dietary fatty acid profiles. All organic plant oils had a positive effect on apparent lipid digestibility compared with the FO diet (P < 0.05), whereas there were no effects on the apparent digestibility of other macronutrients when compared with the FO diet (P > 0.05). Organic vegetable oils did not undergo auto-oxidation as opposed to the FO, and the FO diet consequently had a significantly negative effect on the apparent lipid digestibility. Feed intake was not affected by oxidation of any oils. In conclusion, the study demonstrated that it is possible to fully substitute FO with plant-based organic oils without negatively affecting nutrient digestibility and growth performance. Furthermore, plant-based organic oils are less likely to oxidize than FOs, prolonging the shelf life of such organic diets.

No evidence for a bioenergetic advantage from forced swimming in rainbow trout under a restrictive feeding regime

Sustained swimming at moderate speeds is considered beneficial in terms of the productive performance of salmonids, but the causative mechanisms have yet to be unequivocally established. In the present study, the effects of moderate exercise on the bioenergetics of rainbow trout were assessed during a 15 week growth experiment, in which fish were reared at three different current speeds: 1 BL s−1, 0.5 BL s−1 and still water (≈ 0 BL s−1). Randomly selected groups of 100 fish were distributed among twelve 600 L tanks and maintained on a restricted diet regime. Specific growth rate (SGR) and feed conversion ratio (FCR) were calculated from weight and length measurements every 3 weeks. Routine metabolic rate (RMR) was measured every hour as rate of oxygen consumption in the tanks, and was positively correlated with swimming speed. Total ammonia nitrogen (TAN) excretion rates showed a tendency to decrease with increasing swimming speeds, yet neither they nor the resulting nitrogen quotients (NQ) indicated that swimming significantly reduced the fraction of dietary protein used to fuel metabolism. Energetic budgets revealed a positive correlation between energy expenditure and the current speed at which fish were reared, fish that were forced to swim and were fed restrictively consequentially had poorer growth and feed utilization. The results show that for rainbow trout, water current can negatively affect growth despite promoting minor positive changes in substrate utilization. We hypothesize that this may be the result of either a limited dietary energy supply from diet restriction being insufficient for both covering the extra costs of swimming and supporting enhanced growth.

Rhythmicity and plasticity of digestive physiology in a euryhaline teleost fish, permit (Trachinotus falcatus)

Digestive physiology is considered to be under circadian control, but there is little evidence in teleost fish. The present study explored the rhythmicity and plasticity to feeding schedules of enzymatic digestion in a candidate aquaculture fish, the permit (Trachinotus falcatus). The first experiment identified the rhythms of digestive factors throughout the light-dark (LD) cycle. Gastric luminal pH and pepsin activity showed significant daily variation albeit not rhythmic. These dynamic changes were likewise observed in several digestive enzymes, in which the activities of intestinal protease, chymotrypsin and lipase exhibited significant daily rhythms. In the second experiment, the existence of feed anticipatory activity in the digestive factors was investigated by subjecting the fish to either periodic or random feeding. Anticipatory gastric acidification prior to feeding was identified in periodically fed fish. However, pepsin activity did not exhibit such anticipation but a substantial postprandial increase was observed. Intestinal protease, leucine aminopeptidase and lipase anticipated periodic mealtime with elevated enzymatic activities. Plasma melatonin and cortisol demonstrated robust daily rhythms but feeding time manipulations revealed no significant impact. Plasma ghrelin level remained constant during the LD cycle and appeared to be unaffected by differing feeding regimes as well. Taken together, the digestive factors of permit were highly dynamic during the LD cycle. Periodic feeding entrained digestive physiology and mediated anticipatory gastric acidification and intestinal enzymatic activities. This knowledge will be essential in developing feeding protocols and husbandry-related welfare strategies that will further advance this candidate finfish as an aquaculture species.