Effects of different artificial photoperiods and temperatures on haematological parameters of rainbow trout (Oncorhynchus mykiss)

This study assessed the effects of two artificial photoperiods (LD 24:0 and LD 12:12) and three temperature regimes (9, 11, and 18°C) for 30 days on haematological parameters of trout (Oncorhynchus mykiss) kept in freshwater. Samples were taken at days 7, 14, and 30 during exposure to treatments. A higher mortality (22%) and lower oxygen concentration (<8.0 mg/l) were associated with the combination of photoperiod LD 24:0 and 18°C. The LD 24:0 photoperiod (independently of temperature) increased the haematocrit and the number of erythrocytes at days 7, 14, and 30 (P < 0.01). A temperature of 18°C (independently of photoperiod regimes) diminished the number of total leucocytes, lymphocytes and thrombocytes (P < 0.01). The LD 24:0 photoperiod (also independently of temperature) lowered the number of lymphocytes only after 14 days of experimentation (P < 0.01). Interaction between artificial photoperiod and temperature was only observed at day 14 for polychromatophils (P < 0.01). These results resemble the effects of stress caused by elevated temperatures and the application of continuous light photoperiods, indicating that survival risks may develop in trout farming when this combination is met.     

Effect of light intensity on self-feeding of rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> reared individually

The self-feeding abilities of individually reared rainbow trout Oncorhynchus mykiss were investigated under four different light intensities (7×10⁻², 1×10°, 5×10¹, and 7×10² lx). There was no significant effect of light intensity on self-feeder learning ability and food wastage (which did not exceed 0.5%). However, there was high individual variability in the ability irrespective of light intensity. The total number of trigger actuations was significantly higher at 1×10° lx than at 7×10⁻² and 5×10¹ lx. Feeding patterns during the light phase of a day were classified as early or late in relation to the timing of significant peaks in fish feeding, or non-steady. The last pattern was defined when significant peaks were not observed. Under 7×10⁻², 1×10°, or 7×10² lx, a non-steady feeding pattern was the most common. Early feeding appeared only under the 1×10° lx regime with the random pattern, while the late pattern was observed under 7×10⁻², 5×10¹, and 7×10² lx. Under 5×10¹ lx regime half of the fish fed in the afternoon. These results suggest that light intensity can affect the timing of feeding judged from the frequency of pulling bite tags, but does not affect waste or learning period.     

Effects of constant light on haematological parameters of cultured rainbow trout (Oncorhynchus mykiss) in the Southern Hemisphere

The effects of artificial photoperiod regimes on reproductive patterns have been studied in several species, as have haematological parameters. However, information on how artificial photoperiods may affect blood components is scarce, especially under field conditions. We have assessed the effects of constant light [long day (LD) photoperiod: 24 h (light):0 h (dark)] on haematological parameters of cultured rainbow trout in Chile (Southern Hemisphere). In the initial stage (March up to June), two groups of fish were maintained under similar conditions and under the ambient (natural) photoperiod (NP). One group was then placed under the LD photoperiod regime for 2 months (June/July), following which it was returned to␣the NP (August–January); the control group remained under the NP throughout the experiment (March–January). All fish were assessed for haematological parameters and growth performance at various times during the experiment. During the initial stage, no differences were found between groups. However, at the end of the LD 24:0 period, the LD fish had increased haematocrit values and erythrocyte numbers and diminished mean corpuscular haemoglobin. After the LD fish had been returned to the NP, they developed secondary sexual characteristics and had a 40–44% decrease in the number of leukocytes.     

Polypolar spindle formation during first cell cycle in rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> embryos after heat-shock treatment

ABSTRACT:   Heat shock has been used to inhibit cleavage for the induction of monogenic diploids or tetraploids in animals, but usually the success rate is low. Heat-shocked rainbow trout Oncorhynchus mykiss embryos were used in this histological study to clarify the causes of this low success rate. Embryos treated with hydrostatic pressure were used for comparison. After heat shock had disorganized the spindles, polypolar (tripolar or tetrapolar) spindles in addition to bipolar spindles were often reassembled soon after treatment. The embryos then completed tripolar or tetrapolar division at the first mitosis, and directly turned into three- or four-cell embryos as a result of the first cleavage. During the second mitosis, a monopolar spindle was formed in each blastomere of four-cell embryos and approximately 60% of three-cell embryos. In the remaining three-cell embryos, two of the three blastomeres formed a monopolar spindle, and the third one formed a bipolar spindle. The formation of polypoles is assumed to be caused by insufficient disorganization of daughter centrioles and splitting from the mother centriole by heat shock. Polypolar division is considered to be the cause of aneuploidy and the low success rate of chromosome set doubling. In the case of hydrostatic pressure treatment, the regenerated spindles were bipolar in almost all embryos.     

Effect of a mannan oligosaccharide on the growth performance and immune status of rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

The objective of these experimental trials was to determine the effect of a mannan oligosaccharide (MOS) derived from the outer cell wall of Saccharomyces cerevisiae strain 1026 on the growth performance and immune status of rainbow trout. Two experiments were conducted, one with eight net cages and the other with eight raceways. The net cage experiment (42 days) involved 14,400 fish with an initial average weight of 30 g. The raceway experiment (90 days) was conduced with 40,000 fish with an initial average weight of 101 g. Both experiments compared a commercial extruded diet with and without 2,000 ppm MOS supplementation. The calculated daily feed was supplied in six equal rations. Body weight, feed intake, and mortality were recorded and samples were taken for analysis of indicators of immune status. All data were subjected to ANOVA, with a net cage or raceway regarded as an experimental unit. Significantly improved performance and immune status were observed in the net cage trial—improved weight gain of 13.7% (P < 0.01), reduced feed conversion ratio (FCR) (P < 0.05), reduced mortality (P < 0.01), and improved indicators of immune status (P < 0.01) for fish fed the MOS supplement compared with controls. Similar significantly improved performance was observed for the MOS-treated groups in the raceway trial—9.97% improved weight gain (P < 0.01), lower FCR (P < 0.01), and reduced mortality compared with the control treatment. In the raceway trials, however, only the indicators of immune status lysozyme concentration, APCA, and CPCA were significantly improved by MOS treatment (P < 0.05). These experimental trials demonstrated the ability of MOS to improve the growth performance, survival, and immune status of rainbow trout produced in net cages or raceways.     

The effect of collagenase,water and calcium chloride on the removal of <Emphasis Type="Italic">Salmo salar</Emphasis> (salmon) and <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> (trout) pin bones

The aim of this study was to determine the influence of the fillet structure on the deboning force required to remove salmon and trout pin bones. Salmon and trout fillets with differing fillet structure were used, in order to study the importance of the fillet structure on the deboning process. In the first test naturally gaping and non-gaping fillets were compared. To confirm the role that the collagen plays within the fillet structure, the fillets underwent series of treatments. Fillets were put into (i) a collagenase solution to remove the collagen in the fillet and (ii) a calcium chloride solution to determine if collagen was the main influential factor. Both treated salmon and trout fillets were again compared to untreated fillets from the same batch. The results indicate that collagenase and calcium chloride have a large interaction on deboning force compared to water or no treatments.     

Supplemental effect of bile salts to soybean meal-based diet on growth and feed utilization of rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

A feeding experiment was conducted to evaluate the supplemental effect of bile salts to a defatted soybean meal-based non-fish meal diet for rainbow trout Oncorhynchus mykiss. A fish meal-based diet (FM) and two non-fish meal diets with and without bovine bile salts (SC+B and SC, respectively) were fed to fish (13 g initial weight) for 10 weeks. Fish fed diet SC showed inferior growth and feed efficiency, while bile salt supplementation improved the parameters to the same levels as fish fed diet FM. Crude fat and starch digestibility of diet SC-fed fish decreased after the 10-week feeding trial compared to the data obtained with fish that had no experience of the diet. Total biliary bile salt content and intestinal maltase activity of fish fed diet SC were the lowest among treatments, while these parameters were improved by bile salt supplementation. Morphological changes occurred in the distal intestine and liver of the diet SC group, although the histological features of fish fed diet SC+B were similar to those of fish fed diet FM. These results suggest that bile salt supplementation to a soybean meal-based diet improves the nutrient utilization by normalizing digestive processes in rainbow trout.     

Comparison of fatty acid contents of wild and cultured rainbow trout <Emphasis Type="Italic">Onchorhynchus mykiss</Emphasis> in Turkey

Abstract:   The total lipid content and fatty acid composition were determined in the flesh and skin of wild and cultured rainbow trout in Turkey. The effect of diet content was also investigated on cultured trout. Gas chromatography-mass spectrometry (GC-MS) was used for fatty acid analyses. Total lipid content of skin was higher than flesh in both types and when compared appreciably higher in cultured fish. The predominant fatty acid was palmitic acid (C16:0) in saturated fatty acids and oleic acid (C18:1n-9) in monounsaturated fatty acids. The amount of eicosapentaenoic acid was double in wild and docosahexaenoic acid (DHA) 1.5 times higher in cultured fish flesh. The n-3/n-6 ratio was higher in cultured fish than wild fish. The levels of palmitic, oleic, linoleic (C18:2n-6) and palmitoleic (C16:1n-7) acids were high in skin. The level of EPA was the same in skin of wild fish but 5.5 times higher in cultured fish, whereas the proportion of DHA in skin was lower for wild and 3.5 times higher in cultured fish. Wild fish had a high level of linoleic, arachidonic (C20:4n-6) and linolenic (C18:3n-3) acids. The total amount of n-3 and n-6 polyunsaturated fatty acids was higher in flesh of wild fish than cultured fish, contrary to skin of cultured fish. The data obtained demonstrated that fatty acid composition of cultured fish did not depend on that of feed.     

Probiotic bacteria <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis> influences the blood profile in rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> (Walbaum)

This paper reports the effect of feeding probiotic diets on blood profiles in rainbow trout. Two experiments were performed: in the first, fish of average weight 75 g were offered either a commercial feed or the same incorporated with 10⁹ CFU g⁻¹ of lactic acid bacteria Lactobacillus rhamnosus for 30 days; in the second study performed for a similar duration, fish of average weight 126 g were offered formulated diets that either contained the same bacteria in heat-killed or freeze-dried form (nearly 10¹¹ CFU g⁻¹), or the basal diet without the bacteria. Blood samples were collected at different times after commencement of probiotic feeding to determine the total cholesterol, triglyceride contents, the plasma alkaline phosphatase activity, plasma protein and hematocrit value. The plasma cholesterol significantly increased upon probiotic feeding in the first experiment. A significant elevation (P < 0.05) of plasma cholesterol and triglyceride and alkaline phosphatase activity level was found in the freeze-dried probiotic fed groups at 20 and 30 days postfeeding. This was concomitant with the increased plasma protein and hematocrit values in FD group at 20 and 30 days. Likewise, the heat-killed probiotic fed group registered significantly high values of triglycerides, alkaline phosphatase activity, and plasma protein compared to the control diet fed groups after 20 days of feeding. Thus, alterations in the blood profiles could serve as supplementary information when examining the benefits of probiotics for fish.     

Developmental rates,structural asymmetry,and metabolic fingerprints of steelhead trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) eggs incubated at two temperatures

Temperature stress on developing steelhead (Oncorhynchus mykiss) was evaluated using asymmetry of skeletal characters, fish condition factor, and metabolic fingerprints. Eggs from three female hatchery steelhead were fertilized by a single male. The eggs from each female were divided into two groups and incubated at either 8°C or 18°C. Mortality, growth, and condition factor were measured at stage 6 (32 cells), stage 20 (eyed), and stage 21 (caudal flexing). In addition, ¹H-nuclear magnetic resonance (NMR) spectroscopy was used to establish metabolic fingerprints of developing eggs at the three stages. After hatching, all alevins were moved to tanks at 18°C and allowed to develop to 60 days post-emergence (DPE), at which point they were examined for structural asymmetry. Eggs incubated at 18°C experienced higher mortality, with all eggs from one hen dying at the higher temperature. Eggs incubated at the higher temperature that did survive hatched as larger larval fish than eggs incubated at the lower temperature. Fish incubated at the higher temperature exhibited greater structural asymmetry than fish incubated at the lower temperature. A principle components (PC) analysis of the metabolic fingerprints indicated that PC1 and PC2 accounted for 60% of the variance in the metabolites. Separation along PC1 corresponded to differences in developmental stage, and separation along PC2 corresponded to differences in hen. Eggs incubated at 18°C lagged behind eggs incubated at 8°C along PC1, indicating a potential problem with embryo staging. PC1 scores were highly correlated with the accumulated thermal units during development, indicating that scores along PC1 were a robust measure of developmental stage.     

Effects of chronic high stocking density on liver proteome of rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

The main aim of the present study was to assess the effects of chronic high stocking density on liver proteome of rainbow trout. Rainbow trout juveniles (42.6 ± 2.3 g average body weight) were randomly distributed into six tanks at two stocking densities (low stocking density (LD) = 20 kg m^?3 and high stocking density (HD) = 80 kg m^?3). Both treatments were performed in triplicate tanks for a period of 60 days. High stocking density caused a reduction in the growth performance compared with LD fish. Lysozyme activity increased with stocking density, while serum complement activity presented the opposite pattern. Serum cortisol and total protein levels did not show significant differences (P > 0.05) between experimental groups. The fish reared at high stocking density showed significantly lower osmolality and globulin values but higher albumin level. The HD group had significantly higher activities of catalase, glutathione peroxidase and superoxide dismutase, and malondialdehyde content in the liver when compared to the LD group. Comparative proteomics was used to determine the proteomic responses in livers of rainbow trout reared at high stocking density for 60 days. Out of nine protein spots showing altered abundance (>1.5-folds, P < 0.05), eight spots were successfully identified. Two proteins including apolipoprotein A-I-2 precursor and mitochondrial stress-70 protein were found to increase in HD group. The spots found to decrease in the HD group were identified as follows: 2-peptidylprolyl isomerase A, two isoforms of glyceraldehydes-3-phosphate dehydrogenase, an unnamed protein product similar to fructose-bisphosphate aldolase, 78 kDa glucose-regulated protein, and serum albumin 1 protein.     

Molecular characterization of PRR13 and its tissue-specific expression in rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

The proline-rich protein 13 (PRR13) is reported to be a key regulator of the resistance to cytostatica by decreasing the copy number of the proapoptotic gene thrombospondin-1. We isolated and characterized the complete PRR13 gene sequence of rainbow trout (Oncorhynchus mykiss). The gene comprises four exons and three introns, the latter of comparatively short lengths (100–811 bp). The full-length PRR13 cDNA consists of 1,101 nucleotides, including an open reading frame of 563 bp, which is predicted to encode a 187 amino acid protein with a molecular mass of 18.8 kDa. A continuous stretch of ten serine residues at the C-terminus is highly conserved and characteristic for vertebrate PRR13, but not for other known proline-rich proteins. Phylogenetic analyses suggest a clear separation of teleostean PRR13 proteins and those from mammalian and reptilian species. Comparison of the tissue-specific PRR13 mRNA abundance in two strains of the rainbow trout coastal form (TCO Steelhead II-WA vs. BORN Steelhead II-Germany) revealed an increased expression in the BORN trout in nearly all examined tissues. The major expression differences were detected in gill (2.29-fold) and in liver tissue (2.16-fold). Hence, the increased PRR13 expression in BORN trout might cause improved protection from natural cytostatica and therefore support our assumption that PRR13 is a candidate gene possibly involved in the varying ability of the two rainbow trout strains to handle environmental stress under local conditions of the Southern Baltic.     

Thermal tolerance of a rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> strain selected by high-temperature breeding

ABSTRACT:   Thermal tolerance was studied in a rainbow trout strain successively selected through high temperature breeding at 20–27°C since 1966 in Miyazaki Prefecture, Japan. The hatching rate and fry mortality at high temperatures were examined in the selected strain along with normal strains cultured at water temperature of 9–17°C. The hatching rate of embryos fertilized at either 10 or 14°C and subsequently subjected to high temperatures in the blastula or neurula stage of the selected strain, was marginally higher than that of the normal strain counterparts. The upper 50% lethal temperatures (LT₅₀) for embryos in the early segmentation, blastula and neurula stages of the selected strain were also higher than those of the normal strain counterparts. Death temperatures and LT₅₀ of fries acclimated to 20°C of the selected strain were significantly higher than those of the normal strains. However, no difference in the critical thermal maximum was detected between the different strains. These results suggest that the selected strain of rainbow trout established by selecting successively for many generations at high temperatures acquired a degree of thermal tolerance.     

Effects of dietary <Emphasis Type="SmallCaps">l</Emphasis>-carnitine and chromium picolinate supplementations on performance and some serum parameters in rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

An experiment was conducted to determine the effects of supplemental dietary l-carnitine, chromium picolinate (Cr-Pic) and their combination on growth performance and serum total protein, cholesterol, triglyceride and glucose of rainbow trout (Oncorhynchus mykiss). A total of 276 rainbow trout were randomly allocated to four groups. Fish (average initial body weight = 151 ± 1.69 g) were fed a basal diet without supplemental l-carnitine and chromium picolinate in the control group. The basal diet was supplemented with either 500 mg/kg l-carnitine, 1.6 mg/kg chromium picolinate or 500 mg/kg l-carnitine plus 1.6 mg/kg chromium picolinate for experimental groups 1 (C), 2 (Cr-Pic) and 3 (C + Cr-Pic), respectively. Fish were fed twice a day to apparent satiation for 58 days. Weight gain, growth rate, feed consumption and feed conversion ratio (feed/gain) were calculated for the whole period. At the end of the study, six fish were chosen randomly from each tank to represent the experiment and frozen at −20°C for subsequent dorsal muscle analysis. The results showed no significant differences in final body weight, weight gain or feed conversion ratio among groups. There were also no significant differences in serum total protein, cholesterol, triglyceride or glucose concentrations among groups. Significantly higher lipid concentration of dorsal muscle was observed in experimental groups 1 and 3. In conclusion, supplemental dietary l-carnitine, chromium picolinate and their combination have no beneficial effects on improving growth performance and feed conversion ratio in rainbow trout. However, dietary l-carnitine slightly increased lipid concentration in dorsal muscle of rainbow trout.     

Medicinal plant extracts modulate respiratory burst and proliferation activity of rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) leukocytes

The present study was designed to investigate the immunomodulatory effects of Aloe vera, Curcuma longa, Echinacea purpurea, Lavandula officinalis, Origanum vulgare, Panax ginseng, and Rheum officinale extracts on leukocytes purified from rainbow trout (Oncorhynchus mykiss) head kidney. The cells were cultured in a medium containing increasing doses of extracts; afterwards, they were tested for reactive oxygen species production after stimulation with phorbol myristate acetate (PMA) and proliferation in the presence or absence of phytohemagglutinin from Phaseolus vulgaris (PHA-P). After a 2-h exposure, the extracts of L. officinalis, O. vulgare, and R. officinale strongly reduced the oxidative burst activity of PMA-stimulated leukocytes, in a dose-dependent manner (P ≤ 0.05). A. vera, C. longa, E. purpurea, and P. ginseng extracts reduced this response with lower efficacy and especially at lower concentrations. On the contrary, the highest concentration of ginseng extract stimulated the respiratory burst of leukocytes compared to untreated control cells. After a 72-h exposure, the extracts of L. officinalis, R. officinale, C. longa, E. purpurea, and P. ginseng had a clear dose-dependent stimulatory effect on leukocyte proliferation (P ≤ 0.05). The results suggest that these medicinal plants can be considered as reliable sources of new antioxidants or immunostimulants to be used in aquaculture.     

Stress response of juvenile rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)to chemical cues released from stressed conspecifics

The objective of this study was to determine whether exposure of rainbow trout (Oncorhynchus mykiss) to water containing a stressed trout or skin extract from stressed and non-stressed trout would elicit a stress response in conspecifics. Juvenile rainbow trout were exposed for 1 hour to water containing a stressed fish, homogenized skin extracts from a non-stressed fish, skin extract from a stressed fish and water with none of these factors. The stress response was measured over a 24-h period (1, 6, 12, 24 h after exposure). Plasma cortisol levels increased at 12 h in fish exposed to water from a stressed fish and skin extract from a stressed fish. Plasma glucose and hepatic hsp70 levels were not affected by treatments. The results suggest that rainbow trout elicit a stress response when exposed to stress-related alarm cues released from conspecifics.     

Effect of follicle cell autophagy on gonadal development of triploid female rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

Autophagy is a cellular process which occurs in eukaryotic cells. To study the mechanism regulating polyploid fish growth and development is of significance in genetic, because of its growth advantages and economic values. This study focused on triploid female rainbow trout (RBT) which discusses the effects of autophagy on gonadal development of polyploid fish. Autophagy-related genes of RBT lc3b, atg12, atg4b, gabarap1, and bcl2 were cloned, and autophagy gene expressions in gonads were analyzed at different developmental period. Gonadal ultrastructures were observed under transmission electron microscopy. To detect autophagy protein expression and localization, antibodies of RBT-LC3B and RBT-ATG12 were produced. Results showed clear evidence that autophagy-related genes were highly expressed during 200–300 days post fertilization (dpf), in which autophagosome structures were identified. In this stage, the conversion of LC3B-I to LC3B-II was greater than those in other stages. Immunolabeling-manifested autophagy occurred intensively in the cytoplasm of follicular cells. The morphology of follicular cells was gradually changed, leading to gonadal fibrosis and regression. This autophagic research is a new study area on gonadal development of polyploid fish.     

Sperm quality analysis of normal season (NG) and out-season by photoperiod manipulation (PG) of male rainbow trout broodstock (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

Sperm quality parameters in rainbow trout (Oncorhynchus mykiss) were investigated during normal season spawning (November–January) and out-season spawning (July–August) treated with artificial photoperiod manipulation. Normal spawning males (n?=?15) were kept in an open concrete pond under natural condition. Out-season spawning males (n?=?15) were treated with artificial LED light (50 lm/m²) in a closed concrete pond. In these two experimental groups, five fish were used in each of three spawning periods. The mean weight and body length of males (2?+ years, n?=?30) were 1213.43?±?39.43 g and 45.08?±?0.62 cm, respectively. Sperms were collected from July to August 2016 in the out-season spawning or photoperiod-manipulated group (PG) (water temperature 14.21?±?0.31 °C) and from December 2016 to January 2017, in the normal season spawning group (NG) (water temperature 8.81?±?1.03 °C). Volume of sperm, osmolality of seminal plasma, density of sperm, percentage of motile spermatozoa (MOT), curvilinear velocity (VCL), and duration of motility were measured for each male. Seminal plasma osmolality, density of sperm, and the motility of duration were 358.47?±?37.24 and 308.87?±?44.09, 4.37?±?2.10 and 9.8?±?1.56, and 8.8?±?2.42 and 24.6?±?6.76 in PG and NG, respectively. Fertilization rate was 37.79?±?9.37% and 94.51?±?1.33% in PG and NG, respectively. Sperm quality parameters showed significant differences in most of the cases (p?<?0.05) and fertilization rate at eyed egg stage (150–160 degree-days) was significantly higher in normal season spawning group than the photoperiod-manipulated group (p?<?0.05). Though the rate of fertilization was low in out-season, it was able to get enough gametes in summer using only artificial light having no changes in other parameters.