Preventive efficacy of sodium hypochlorite against water mold infection on eggs of chum salmon Oncorhynchus keta

ABSTRACT:   To protect chum salmon eggs from water mold infection during incubation, the eggs were treated daily with sodium hypochlorite solution (NaOCl) at 10 mg/L residual chlorine concentration for 15 min during their developmental period from fertilization to eyed stages. The number of infected eggs and number of eyed eggs were observed on day 23 of incubation. The percentage of infected eggs to total eggs was significantly lower with NaOCl treatment (1.8 : 33.4%) than in the control (11.3 : 59.3%, P  < 0.01). The percentage of eyed eggs to total eggs was significantly higher with NaOCl (85.9 : 98.6%) than in the control (66.1 : 97.5%, P  < 0.01). The antifungal activity of NaOCl resulted in improving egg survival. Accordingly, NaOCl is a useful antifungal agent against water mold infection on chum salmon eggs.     

Changes in fertility of rainbow trout eggs retained in coelom

ABSTRACT:    Effects of prolonged retention time of ovulated eggs in the parental coelom on fertilization success were studied in rainbow trout Oncorhynchus mykiss using cryopreserved sperm with a uniform fertilizing ability. Proportions of successful fertilization, eyed eggs and hatched alevins were examined at different time periods up to a retention time of 14 days beyond the ordinary stripping time, and were compared with eggs incubated in artificial coelomic fluids (ACF). Eggs that were retained longer in the coelom showed gradual decreases in all the proportions of successful fertilization, eyed eggs and hatched alevins. The progress of cleavage after fertilization slowed with prolonged retention times. Eggs incubated in ACF lost their fertilizing ability much sooner than those retained in the coelom. The hatching rate of eggs retained for 2 weeks in coelom was 36%, while it was 1% in those eggs incubated for 4 days in ACF. Thus, eggs retained in the coelom showed higher fertilization success than those incubated in ACF.     

Evidence of concealment behavior by adult rainbow trout and brook trout in winter

Abstract – There has been little investigation of the winter ecology of adult trout during winter, especially in regard to concealment behavior. We compared day vs night underwater counts of adult rainbow trout and brook trout from four streams. At water temperatures between 1°C and 9°C, daytime counts accounted for 44% and 16% of nighttime snorkeling counts for rainbow trout and brook trout adults, respectively. As winter progressed, nighttime counts declined more so for brook trout than rainbow trout, but the decline was not significant for either species. Nocturnalism of both species was higher in streams with colder water temperatures. We observed few fish within concealment structure; however, by electrofishing concealment habitat during the day, we captured 10 times more adult trout than we counted immediately beforehand by snorkeling. Adult trout were concealed in cobble-boulder substrate and woody debris during the day. ^Note     

Competitive exclusion of brown trout Salmo trutta L., by rainbow trout Oncorhynchus mykiss Walbaum, in lake tributaries, New Zealand

Spawning runs of brown trout Salmo trutta L., and rainbow trout, Oncorhynchus mykiss Walbaum, were compared in three tributaries of two lakes for timing, numbers and redd characteristics. Redd characteristics for the two species in four other streams were examined. No significant differences in redd characteristics between the two species were observed, but in all lake tributaries the possibilities of superimposition of spring spawning rainbow trout on redds of brown trout were examined. A common feature was the high ratio of numbers of spawners to the area of preferred spawning gravel, and it was concluded that in the lake tributaries, superimposition resulted in increased mortality of brown trout eggs, and in one case elimination of the brown trout population. Management possibilities for control of the species proportions in comparable situations are discussed.     

Passive immunization of rainbow trout,Oncorhynchus mykiss (Walbaum), against Flavobacterium psychrophilum,the causative agent of bacterial coldwater disease and rainbow trout fry syndrome

Flavobacterium psychrophilum, the causative agent of bacterial coldwater disease (CWD) and rainbow trout fry syndrome (RTFS), causes high mortality in cultured salmonids. The present study was designed to determine the role antibody plays in conferring protection to rainbow trout fry, Oncorhynchus mykiss (Walbaum), by passive immunization with convalescent serum or serum from adult rainbow trout immunized with F. psychrophilum, and goat anti-F. psychrophilum serum. In each experiment, rainbow trout fry were injected intraperitoneally with antiserum and challenged by subcutaneous injection with a virulent strain (CSF-259-93) of F. psychrophilum 24-h post-immunization. Relative percentage survival (RPS) ranged from 9-42% when rainbow trout fry (mean weight 1.3 g) were injected with a 1:2 dilution of 25 microL of convalescent serum ranging in enzyme-linked immunosorbent assay antibody titres from 1600-102400. Rainbow trout fry (mean weight 1.0 g) passively immunized with 25 microL of serum from immunized adult fish exhibited RPS values of up to 57%. In each of these experiments, RPS increased with increasing antibody titres against F. psychrophilum. Passive immunization with 25 or 50 microL goat anti-F. psychrophilum serum, however, did not confer protection to fry (mean weight 1.3 g). These results suggest that trout antibody plays a role in conferring protection to F. psychrophilum, but antibody alone is unable to provide complete protection.     

Effects of egg aging on the metabolites of ovarian fluid in rainbow trout,Oncorhynchus mykiss

Nuclear magnetic resonance ‐based metabolomics was applied to study effects of egg aging on ovarian fluid metabolites in rainbow trout, Oncorhynchus mykiss. The eggs of three females were pooled and then assigned to three plastic vials for 18 days in vitro storage at 4°C. Ovarian fluid samples were taken 0, 6, 12 and 18 days after storage. Three groups of metabolites including amino acids, osmolytes and energy metabolites were found to change during storage period. The glucose levels of ovarian fluid showed significant decreases on days 12 and 18 after storage (p < .05). For acetoacetate and acetate, significant increases were observed, respectively, on days 12 and 18 after storage (p < .05). The creatine levels of ovarian fluid increased significantly on days 12 and 18 after storage (p < .05). Lactate levels in ovarian fluid elevated during storage period (p < .05). Glycerol levels showed a significant increase on days 12 and 18 after storage (p < .05). The values of osmolytes in ovarian fluid (e.g., betaine, taurine, trimethylamine‐N‐oxide, N,N‐dimethylglycine) showed a decreasing trend on day 12 which continued until the end of storage on day 18 (p < .05). Almost all amino acids elevated on days 12 and 18 after storage (p < .05). After an apparent elevation in isoleucine levels on days 6 and 12, this amino acid decreased on day 18 after storage (p < .05). The osmolytes might act as antioxidant against free‐radicals produced as a result of over‐ripening. Glucose can be used as energy resource for eggs and bacteria during ova storage. Also, change pattern of amino acids indicate hydrolysis of proteins as the time of storage increases.     

Modelling effects of climate change on Michigan brown trout and rainbow trout: Precipitation and groundwater as key predictors

Understanding how changes in stream temperature affect survival and growth of coldwater fishes, including brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss), is important for conserving coldwater stream fisheries in a changing climate. However, some contemporary stream temperature models assume spatially uniform (i.e. unrealistic) air–stream temperature relationships or demand hydrometeorological predictors (e.g. solar radiation and convection) that are expensive and often impractical for fisheries managers to measure. As such, we produced a relatively cost-effective, management-relevant modelling approach for predicting effects of changes in air temperature, precipitation and groundwater inputs on stream temperature and, consequently, the survival and growth of brown trout and rainbow trout in Michigan, USA. We found that precipitation- and groundwater-corrected stream temperature models (mean adjusted R² = .77, range = 0.65–0.88) performed better than linear air–stream temperature models (mean adjusted R² = .59, range = 0.21–0.80). Stream temperature was projected to increase by 0.07–3.88°C (1%–22%) with simulated changes in air temperature, precipitation and groundwater inputs. The greatest warming was predicted for surface runoff-dominated sites with limited groundwater-driven thermal buffering, where thermal habitat suitability for salmonid survival and growth declined 20%–40%. However, groundwater-dominated sites may not be immune to temperature warming, especially if groundwater temperature increases or groundwater inputs decline in a changing climate. Our modelling approach provides a reliable, cost-effective method for predicting effects of climate change on brown trout and rainbow trout survival and growth, allowing for strategic management actions to increase the thermal resilience and sustainability of salmonid populations (e.g. groundwater conservation and riparian/watershed rehabilitation).     

Selective predation of threespine stickleback by rainbow trout

Abstract – Threespine stickleback (Gasterosteus aculeatus) with divergent pelvic phenotypes from Wallace Lake, Alaska, were exposed to rainbow trout (Oncorhynchus mykiss) to test for selective predation. Trout more often successfully preyed upon individuals with pelvic reduction, which supports the hypothesis that robust pelvic girdles are maintained in stickleback populations because of selection by fish predators. Stickleback with complete pelvic girdles experienced a higher incidence of wounds from unsuccessful predation attempts, although this finding was not statistically significant, possibly because of low frequencies of wounded individuals. Spines likely facilitate postcapture defence, although stickleback with spines may also be less targeted by trout. This study supports the hypothesis that stocked rainbow trout pose a conservation threat to pelvic‐reduced stickleback populations.     

Morphological, physiological and biochemical parameters characterizing the over-ripening of rainbow trout eggs

In rainbow trout (Oncorhynchus mykiss) freshly ovulated eggs and over-ripened eggs which had been retained in the coelomic cavity for 7, 14 and 21 days were investigated in aspects of morphology, physiology and biochemistry. Egg viability was significantly reduced from 85.9±16.4% in freshly ovulated eggs to 25.1±21.9% in over-ripened eggs which had been retained in the coelomic cavity for 21 days. Further during over-ripening in the ovarian fluid the pH significantly decreased, while the levels of proteins, of esterified and non esterified fatty acids and the activities of aspartate aminotransferase and acid phosphatase significantly increased. Also egg parameters changed: the wet weight of the unhardened eggs increased, the weight increase during hardening and the levels of esterified and of non esterified fatty acids significantly decreased. In freshly ovulated eggs the yolk consisted of a homogenous mass and the perivitelline space was small, but in over-ripened eggs the yolk was non homogenous with numerous vesicular inclusions and the perivitelline space was enlarged. When freshly ovulated eggs were incubated in water the cortical reaction was detectable within 5 min, in over-ripened eggs hardly no extrusion of cortical vesicles was visible and the width of the perivitelline space was very irregular.For the investigated freshly ovulated and over-ripened samples the egg viability significantly correlated with ovarian fluid parameters (pH, protein, non esterified fatty acids, esterified fatty acids, aspartate aminotransferase, acid phosphatase) and egg parameters (weight increase during hardening, weight of the hardened eggs).     

Dietary requirements of rainbow trout for tryptophan,lysine and arginine determined by growth and biochemical measurements

Three separate studies were performed to determine the dietary requirements of rainbow troutSalmo gairdneri for tryptophan (Trp), lysine (Lys) and arginine (Arg) from both growth and biochemical data. The growth studies were carried out over a 12 week period. From graphical plots of % mean weight gain against % amino acid in diet the following requirement values were obtained, Trp 0.25% diet (0.4% dietary crude protein); Lys 1.9% diet (4.3% dietary protein); and Arg 1.6–1.8% diet (3.6–4% dietary protein). Plasma and liver amino acid concentrations measured 20h after feeding did not prove useful for determination of requirement values. Hepatic activities of Trp pyrrolase (TP), Lys ketoglutarate reductase (LKGR) and arginase were not significantly affected by varying levels of Trp, Lys and Arg respectively in the diet. TP has a cytosolic location and a Km of 0.2 mM for Trp; LKGR is mitochondrial and the Km for Lys is 7.3 mM; arginase is also mitochondrial and has a Km of 4.9 mM for arginine. Measurements of expired¹⁴CO₂, after injection of a tracer dose of¹⁴C amino acid, did allow estimates of requirement levels to be made. The values obtained from the oxidation studies reinforced the values obtained from the growth data but were not precise enough to justify using this method on its own.     

The garlic component,allicin, prevents disease caused by Aeromonas hydrophila in rainbow trout,Oncorhynchus mykiss (Walbaum)

Allicin was fed at 0 (= control), 0.5 and 1.0 mL of Allimed^® liquid 100 g^?1 of feed for 14 days to rainbow trout, Oncorhynchus mykiss (Walbaum), fingerlings before infection with Aeromonas hydrophila with a resultant reduction in mortalities from 80% in the controls to 8% [relative percentage survival (RPS) = 90%] and 0% (RPS = 100%) among the treated fish. Allicin was strongly antibacterial compared to the control, with a minimum inhibitory concentration (MIC) of >400 μL mL^?1 of Allimed^® liquid. Use of allicin led to a lower number of white blood cells (132.0 ± 0.4 × 10³) compared to 175.0 ± 0.1 × 10³ in the controls, but elicited increased phagocytic activity, i.e. a phagocytic value of 39.2% compared to 13.6% in the controls, and serum lysozyme activity, which showed significant (P > 0.05) differences compared to the control at 15 and 30 min after the first reading at 0 min of incubation.     

Effects of the extensive culture system as finishing production strategy on biometric and chemical parameters in rainbow trout

The effect of finishing extensive farming period, to reduce fat content and manipulate the fatty acid profile of fish muscle, was evaluated in rainbow trout. Fish were stocked in an artificial lake, in which fish were fed only on naturally available nutrients with no supply of artificial feed, for different lengths of time from 0 to 120 days. No weight loss was noted during the whole finishing period while total length increased from 228±7 to 269±3 mm and the condition factor decreased from 1.41±0.04 to 0.89±0.02. The total fat content of the fillets decreased considerably from 4.7±0.6% at the beginning to 2.4±0.4% and 0.7±0.2% after 45 and 120 days respectively. Fillet fatty acid composition was affected by the time of stocking in the extensive farm. In contrast to the reduction in C18:1n‐9, C18:2n‐6, total monounsaturated fatty acid and total n‐6 percent values, an increase in the C20:5n‐3, C22:6n‐3, total polyunsaturated fatty acid and total n‐3 percent values was observed. It was shown that while other finishing strategies for salmonids have some disadvantages, the extensive culture system seems to be a potentially useful tool for increasing the general quality of the end product.     

In vitro and in vivo antifungal activity of Satureja cuneifolia ten essential oil on Saprolegnia parasitica strains isolated from rainbow trout (Oncorhynchus mykiss,Walbaum) eggs

In the present study, the chemical composition and the antifungal properties against Saprolegnia parasitica (in vitro and in vivo) of the essential oils of thyme (Satureja cuneifolia) from Mediterranean region of Turkey were evaluated for the first time. The composition of oils was analysed using gas chromatography/mass spectrometry (GC/MS). The major constituents of oil of S. cuneifolia were cavracrol (46,84%) and cymene (16.90%). Antifungal effects of S. cuneifolia essential oil against S. parasitica strains (A1 and E1) were detected by disc diffusion and tube dilution assays. The antifungal effect of S. cuneifolia was determined to be stronger against S. parasitica E1 isolate (MIC 50 μL mL^?1, MLC 250 μL mL^?1) compared with S. parasitica A1 isolate (MIC 50 μL mL^?1, MLC 500 μL mL^?1). Following in vitro assays, effective doses of S. cuneifolia for disease control in rainbow trout eggs experimentally infected with S. parasitica were investigated. For this aim, infected eggs were treated with the essential oil (0, 5, 10, 20 and 50 ppm) during incubation period (21 days) after fertilization. Formalin (5 mL L^?1) was used as positive control. Hatching rate of eggs at the end of incubation period were calculated. The highest hatching rates were recorded in S. parasitica E1 strain at 5 and 10 ppm concentrations of S. cuneifolia and in S. parasitica A1 strain at 10 and 20 ppm (P < 0.05).