Effects of experimental anaemia on intra-erythrocytic phosphate levels in rainbow trout, Oncorhynchus mykiss

The concentrations of intra-erythrocytic adenylates (ATP, ADP and AMP) and guanylates (GTP, GDP and GMP) were determined in rainbow trout subjected to 10% blood removal every 12 h for 96 h. Haemoglobin concentration, [Hb], decreased from 6·043±0·617 to 0·957 ± 0·195 g dl⁻¹. This decrease in [Hb] was followed by a continuous increase in total organic phosphates, e.g. adenylates plus guanylates. Intra-erythrocytic NTP (ATP plus GTP) levels increased significantly after 48 h when haemoglobin concentration was 2·427 ± 0·256 g dl⁻¹. Although a significant increase in GDP levels in animals with [Hb] less than 1·677 ± 0·235 g dl⁻¹ was observed, the general increase in guanylate level was mainly due to the GMP which increased about 85-fold during the experimental period. It is suggested that the erythrocytes of anaemic rainbow trout have the capacity to increase NTP/Hb₄ ratios which may represent an advantage for anaemic fish.     

Response of serum carotenoid levels to dietary astaxanthin and canthaxanthin in immature rainbow trout Oncorhynchus mykiss

Rainbow trout were fed a diet supplemented with astaxanthin (89 mg/kg) or canthaxanthin (116 mg/kg) in two different experiments: experiment 1 was designed to measure the kinetics of the appearance and disappearance of carotenoids in the serum; experiment 2 was undertaken to establish the serum dose-response to synthetic astaxanthin and canthaxanthin for immature rainbow trout. The serum carotenoid concentrations of immature rainbow trout increased when fish were fed carotenoid supplemented feed and then reached a plateau after 1 day of intake for astaxanthin and after 2 days for canthaxanthin. Circulating astaxanthin represented a value 2.3 times that of canthaxanthin. After dietary supplementation was discontinued, the serum carotenoid concentrations decreased within 3 days for both carotenoids. The average decreasing slopes for the two carotenoid pigments were parallel, indicating a similarity in the rate of which astaxanthin and canthaxanthin are utilized by rainbow trout. The serum dose-response of trout that received dietary keto-carotenoids increased with increasing pigment levels. The hypothesis that absorption of dietary carotenoids in 12.5–200 mg/kg range of concentration across the gut wall may be by passive diffusion is proposed.     

Microsatellite diversity in cultured populations of rainbow trout Oncorhynchus mykiss in China

Twenty microsatellite loci were examined to assess genetic variation among six cultured populations of rainbow trout introduced to China. Fourteen polymorphic loci showed moderate levels of diversity within and between populations.     

The effects of dietary protein:energy ratio and amino acid pattern on nitrogen utilization and excretion of rainbow trout Oncorhynchus mykiss (Walbaum)

This study was undertaken to investigate: (1) the effects of both deficiencies and excesses in essential amino acids (EAAs) from an estimated optimum dietary EAA pattern on nitrogen (N) utilization and excretion of rainbow trout Oncorhynchus mykiss, (2) the effects of dietary digestible protein (P_D): digestible energy (E_D) ratio (P_D:E_D) on N utilization and excretion of O. mykiss and (3) the potential interaction of these two factors. A 3 × 3 factorial experiment was conducted, with the two factors EAA pattern and P_D:E_D ratio. The three levels of EAA pattern were: (1) optimum EAA pattern, (2) 60% deficiencies in the three amino acids arginine, histidine and lysine, and (3) 60% excesses in the three amino acids arginine, histidine and leucine. The three levels of P_D:E_D ratio were 18, 21 and 24 g MJ^?1. Amino acid deficiencies from an optimum amino acid pattern caused reductions in mean N retention of 29 to 37%, with the greatest reduction associated with the lowest P_D:E_D ratio, and similar substantial increases in total N and ammonia‐N excretion at all of the dietary P_D:E_D ratios investigated. Amino acid excesses, however, did not negatively affect N retention or excretion. Increasing P_D:E_D ratio was associated with decreasing N retention and increasing N excretion over the range of dietary protein and lipid levels tested. Results of this study showed that a diet with optimum dietary amino acid pattern and lowest P_D:E_D ratio produced the highest N retention (47% of ingested N) and the lowest total N and ammonia‐N excretion of O. mykiss.     

Effects of dietary astaxanthin supplementation on reproductive characteristics of rainbow trout (Oncorhynchus mykiss)

The effect of dietary astaxanthin supplementation on reproductive characteristics was investigated in five groups of female rainbow trout broodstock fed diets containing either 0.07, 12.46, 33.33, 65.06 or 92.91 mg astaxanthin kg^?1, respectively, and two groups of male rainbow trout broodstock fed diets supplemented with 0.07 and 33.33 mg astaxanthin kg^?1, respectively, for 6 months in an artificial photoperiod system until sexual maturation. The eggs from each group of female broodstock were divided into two equal batches. One batch was fertilized with homogenized sperm of four males fed diets with 0.07 mg astaxanthin kg^?1 and the other portion with sperm of four males fed diets with 33.3 mg astaxanthin kg^?1. The females produced eggs with astaxanthin concentrations ranging from 2.03 to 29.79 mg kg^?1. Dietary astaxanthin supplementation had positive effects on investigated reproductive traits. Significant differences in rate of fertilization, percentage of eyed and hatched eggs, and mortality of eyed eggs were found between treatments (P < 0.05), but no significant difference was found on percentage of mortality before hatching (P > 0.05). A significant difference (P < 0.05) in fertilization rate was found for male groups fed 0.07 and 33.3 mg astaxanthin kg^?1. The astaxanthin content in the eggs and fertilization rate, eyed‐egg percentage and percentage hatch were significantly correlated (P < 0.05). It is concluded that dietary supplements of astaxanthin are required for optimum reproduction in rainbow trout.     

Effects of dietary Ergosan on cutaneous mucosal immune response in rainbow trout (Oncorhynchus mykiss)

The effects of dietary Ergosan on the growth performance and mucosal immunity in rainbow trout skin were investigated. 60 rainbow trout (100-110 g) were randomly assigned to 2 groups in triplicates and fed one of the experimental diet formulated with 5 g kg⁻¹ Ergosan or control diet for 50 days. Results showed that on the 45th day of feeding trial, Ergosan supplementation significantly enhanced the growth performance compared to control group. Various enzyme activities, namely lysozyme, protease, alkaline phosphatase and esterase in treatment group were also enhanced on the 45th and 50th day. Skin mucus in Ergosan-fed fish showed the agglutination of erythrocytes while in control group, no visible agglutination was shown. In addition, skin mucus in treatment group showed strong antibacterial activity against Yersinia ruckeri. In conclusion, the major immune components of rainbow trout mucus that are involved in the non-specific immunity were enhanced by administration of Ergosan in 5 g kg⁻¹.     

Parental stress‐coping styles affect the behaviour of rainbow trout Oncorhynchus mykiss at early developmental stages

This work examined behavioural responses in yolk‐sac rainbow trout Oncorhynchus mykiss larvae originating from strains selected for high (HR) or low (LR) plasma cortisol response to a standardized stressor. The results showed that yolk‐sac larvae originating from the HR strain were more sensitive to environmental stressors, in that they showed a shorter reaction time to low oxygen levels. Previous studies on adult and juvenile individuals from these strains demonstrated a number of correlated physiological and behavioural differences. In yolk‐sac larvae, growth and development depended mainly on internal factors, which suggest that at least some aspects of stress‐coping styles are inherent to the individual, before factors such as social experience or variable access to food resources could modify behavioural strategy.     

Dietary carotenoid pigment supplementation influences hepatic lipid and mucopolysaccharide levels in rainbow trout (Oncorhynchus mykiss)

We assessed the effects of dietary carotenoid pigment supplementation on liver histochemistry in the rainbow trout. One hundred and eight rainbow trout (mean mass 266 ± 10 g) were assigned to each of three replicate tanks for each of three dietary treatments; astaxanthin, canthaxanthin, or control at a target dietary inclusion of 100 mg/kg, by top-coating a pigment-free commercially extruded basal diet (Trouw Aquaculture, U.K.). Fish were fed for 3 weeks at a ration of 1.2% body mass/day, in a recirculating freshwater system maintained at 16 °C. Frozen liver sections were stained for total lipids, unsaturated lipids, glycogen, mucopolysaccharides, glycogen phosphorylase and aspartate aminotransferase. Relative amounts were measured quantitatively by image analysis. Carotenoid treatment significantly (P < 0.05) altered the total lipid profile and hepatic mucopolysaccharide contents of livers of rainbow trout. Results are discussed in relation to the catabolic potential of the liver in carotenoid pigment metabolism.     

Effects of dietary thymol‐carvacrol on growth performance,hematological parameters and tissue composition of juvenile rainbow trout,Oncorhynchus mykiss

Growth performance, carcass quality, survival and hematological responses of Oncorhynchus mykiss juveniles (initial weight 8.4 ± 0.1 g) fed diets containing thymol‐carvacrol powder at the levels of 0, 1.0, 2.0, 3.0 g kg^?1 were tested. Thymol‐carvacrol powder originated from Origanum vulgare, a Mediterranean plant, added to diets. Each diet was fed to triplicate groups of fish for 45 days. Fish fed diets containing thymol‐carvacrol had significantly higher final weight and growth than the control group. Food conversion ratio in fish fed diets containing 2.0 and 3.0 g kg^?1 thymol‐carvacrol was statistically better than in other treatments. Survival was not different among all treatments. The number of lymphocytes increased when thymol‐carvacrol was used at higher levels. Furthermore, whole body lipid content was higher in fish fed 1.0 and 2.0 g kg^?1 thymol‐carvacrol than the other groups, but body protein in the group fed 3.0 g kg^?1 was higher than in other groups. Also, body ash in control and 1.0 g kg^?1 was higher than in other groups. Whole body dry matter was not affected by dietary treatments. These results indicated that dietary administration of thymol‐carvacrol can influence some growth, hematological parameters and tissue composition in rainbow trout juveniles.     

Cannibalism in non‐native brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss stream‐dwelling populations

Introduced and allopatric populations of brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss were sampled in Slovenia for stable isotope analysis to assess dietary niche shifts through ontogeny and estimate the propensity for cannibalism. Both S. trutta and O. mykiss are cannibals, with higher average relative contribution of conspecific assimilated energy for S. trutta (27·9%) compared with O. mykiss (7·7%). The smallest cannibal was 166 mm in the S. trutta population and 247 mm in the O. mykiss population.     

Effects of low protein intake on extra-hepatic gluconeogenic enzyme expression and peripheral glucose phosphorylation in rainbow trout (Oncorhynchus mykiss)

The objective of the study described here was to analyze in rainbow trout (Oncorhynchus mykiss) the effects of low protein intake on peripheral glucose phosphorylation capacities and gluconeogenic enzymes in kidney and intestine. Fish were food-deprived for 14 days or kept under a low and a high protein intake regime using a pair feeding protocol in order to maintain constant carbohydrate and lipid intakes. We analyzed the effect of protein restriction on (i) hepatic, renal and intestinal fructose-1.6-bisphophatase (FBPase) and glucose-6-phosphatase (G6Pase) enzymes at the molecular and enzymatic levels and (ii) glucose phosphorylation activities (hexokinases) in the liver, peri-visceral adipose tissue, red muscle and white muscle. Irrespective of the nutritional status, we observed the same levels of hexokinase activities in all the tissues studied. Renal G6Pase and FBPase gene expression and activities were not modified among the groups. In contrast, there was increased intestinal FBPase gene expression in fish under a low protein intake and higher G6Pase activities in both groups of fed fish. This result differs from what is observed in rats and suggest a role of intestine in the regulation of postprandial gluconeogenesis in fed trout. In conclusion, our data did not demonstrate any specific effect of low dietary protein intake to either gluconeogenic capacities or glucose phosphorylation capacities in rainbow trout.     

Primary culture and histological characterization of phagocytic cells from rainbow trout Oncorhynchus mykiss

In this study the pronephros of rainbow trout Oncorhynchus mykiss was explanted and cultured. The morphology of cultured cells suggested they were leukocyte derived. To confirm this, cells were incubated with non-opsonized fluorescent beads and human apoptotic polymorphonuclear leukocytes (PMN) to establish that they were capable of phagocytosis and that they became activated following exposure to apoptotic bodies. The cells were studied using light microscopy, transmission electron microscopy and a live cell observer system. Cells in culture were also stained with phalloidin to identify actin reorganization following activation. Cultured cells ingested the inert beads and apoptotic PMNs and c . 80% of cells became activated following exposure to the apoptotic PMN, evidenced by enhanced filopodial extensions. This methodology may play a role in future studies, in particular, the competence of macrophages following exposure to radiation can now be tested.     

Amitosis‐like nuclear division in erythrocytes of triploid rainbow trout Oncorhynchus mykiss

This work shows that the atypical erythrocytes in triploid rainbow trout Oncorhynchus mykiss were morphologically similar to those of toads. The nuclei of the cells can be bell‐shaped, constricted or irregular. It is presumed that such nuclear division is probably amitosis.     

Evaluation of tissue changes following intramuscular infiltration of lidocaine in rainbow trout Oncorhynchus mykiss

Rainbow trout Oncorhynchus mykiss were infiltrated with either saline or lidocaine adjacent to the dorsal fin to assess histopathological changes. Infiltration was done as if it were being used as a local anaesthetic. Tissue lesions and associated tissue healing were examined over a period of 30 days. Most changes occurred at the cranial site of where the solution was first infiltrated. The infiltration of a dose of 10 mg kg^?1 of lidocaine appears to have damaged the skeletal muscle and connective tissues more than a similar volume of saline, especially during the first 15 days. The primary changes included haemorrhage, inflammation and muscle degeneration and necrosis. By day 30 post‐infiltration inflammatory lesions were either nearly or completely absent, signs of myofibre regeneration were noted in only one fish. This experiment shows local anaesthetics and saline can produce localized tissue damage, especially during the first 2 weeks post infiltration. Care should be taken to allow the fish to heal for at least 30 days and probably more, no matter the solution administered, especially if giving repeated injections or infiltrations at the same site.     

Priming of host resistance to protect cultured rainbow trout Oncorhynchus mykiss against eye flukes and parasite‐induced cataracts

In the present study, immunologically naive rainbow trout Oncorhynchus mykiss were experimentally exposed to a low‐level Diplostomum spathaceum (Trematoda) infection to stimulate acquired resistance and, along with unexposed controls, were subsequently exposed to natural infection for 8 weeks. The priming of the host resistance, designed to simulate a procedure applicable in aquaculture, decreased the number of establishing parasites compared to untreated controls by the end of the experiment. This effect was slow and did not protect the fish against the parasite‐induced cataracts. The results suggest that this type of priming of host resistance is probably inefficient in preventing the deleterious effects of D. spathaceum infection in aquaculture conditions.     

Environmental influences on cardiovascular variables in rainbow trout, Oncorhynchus mykiss (Walbaum)

Two groups of wild (lakedwelling and anadromous), and a group of hatchery-reared Oncorhynchus mykiss (Walbaum) (rainbow trout) were sampled in order to measure cardiac morphometrics, haemoglobin concentration, and the DNA and protein concentration in cardiac muscle. A combination of these variables was used to distinguish wild fish from domestic ones.
The wild fish had significantly higher levels of haemoglobin (for male fish, 10.10 and 10.07 g 100 ml⁻¹ vs. 7.69 g d⁻¹) and larger relative ventricle mass (females, 0.091 and 0.099% ofbody mass vs. 0.073%; males, 0.108 and 0.134% vs. 0.102%; immatures, 0.086 and 0.094% vs. 0, 072%, respectively) than the domestic fish. The anadromous and domestic fish had significantly higher amounts of compact tissue when compared with lake fish (females, 43 and 47% of ventricle mass vs. 34%, respectively). Ventricle size distinguished wild fish from domestic fish, except male anadromous and male domestic fish which were distinguished only by haemoglobin and compact tissue values. Immature fishes from all groups had lower total protein levels in the ventricle, lower compact tissue levels, and less haemoglobin. Points regarding the potential environmental influences in determining these cardiovascular trends are discussed.