Exploring the effects of dietary inulin in rainbow trout fed a high‑starch,100%plant‑based diet

Background High dietary carbohydrates can spare protein in rainbow trout(Oncorhynchus mykiss)but may affect growth and health.Inulin,a prebiotic,could have nutritional and metabolic effects,along with anti-inflammatory properties in teleosts,improving growth and welfare.We tested this hypothesis in rainbow trout by feeding them a 100%plant-based diet,which is a viable alternative to fishmeal and fish oil in aquaculture feeds.In a two-factor design,we examined the impact of inulin(2%)as well as the variation in the carbohydrates(CHO)/plant protein ratio on rainbow trout.We assessed the influence of these factors on zootechnical parameters,plasma metabolites,gut microbiota,production of short-chain fatty acids and lactic acid,as well as the expression of free-fatty acid receptor genes in the mid-intestine,intermediary liver metabolism,and immune markers in a 12-week feeding trial.Results The use of 2%inulin did not significantly change the fish intestinal microbiota,but interestingly,the high CHO/protein ratio group showed a change in intestinal microbiota and in particular the beta diversity,with 21 bacterial genera affected,including Ralstonia,Bacillus,and 11 lactic-acid producing bacteria.There were higher levels of butyric,and valeric acid in groups fed with high CHO/protein diet but not with inulin.The high CHO/protein group showed a decrease in the expression of pro-inflammatory cytokines(il1b,il8,and tnfa)in liver and a lower expression of the genes coding for tight-junction proteins in mid-intestine(tjp1a and tjp3).However,the 2%inulin did not modify the expression of plasma immune markers.Finally,inulin induced a negative effect on rainbow trout growth performance irrespective of the dietary carbohydrates.Conclusions With a 100%plant-based diet,inclusion of high levels of carbohydrates could be a promising way for fish nutrition in aquaculture through a protein sparing effect whereas the supplementation of 2%inulin does not appear to improve the use of CHO when combined with a 100%plant-based diet.

Short-Term Stress Response of Juvenile Rainbow Trout Subjected to Two Different Rearing Densities

Juvenile rainbow trout Oncorhynchus mykiss were subjected to one of four treatments in a two-by-two experimental design: 1) fed at a density of 1.8 g/m3, 2) Fasted at 1.8 g/m3, 3) fed at 30.1 g/m3, and 4) fasted at 30.1 g/m3. Blood glucose and hematocrit were measured at 4, 6, 48, 168, and 336 hours after placement in one of the two rearing densities, with relative fin lengths and organosomatic indices recorded at 336 hours. Glucose levels over time were not significantly different among the density and feeding treatments. Hematocrit levels over time were also not significantly different. Total lengths, weight, hepatosomatic index, viscerosomatic index, and any of the relative fin lengths were not significantly different between the high and low densities. However, the hepatosomatic index was significantly greater in the fed fish compared to those fasted. The splenosomatic index was significantly greater in the higher density treatment. These results likely indicate no short-term stress response to the higher rearing density used in this short-term experiment and no interaction between starvation and density-related stressors.

Effects of full replacement of dietary fishmeal with insect meal from Tenebrio molitor on rainbow trout gut and skin microbiota

Background:Aquaculture must continue to reduce dependence on fishmeal(FM)and fishoil in feeds to ensure sustainable sector growth.Therefore,the use of novel aquaculture feed ingredients is growing.In this regard,insects can represent a new world of sustainable and protein-rich ingredients for farmed fish feeds.Accordingly,we investigated the effects of full replacement of FM with Tenebrio molitor(TM)larvae meal in the diet of rainbow trout(Oncorhynchus mykiss)on fish gut and skin microbiota.Methods:A feeding trial was conducted with 126 trout of about 80 g mean initial weight that were fed for 22 weeks with two isonitrogenous,isolipidic,and isoenergetic extruded experimental diets.Partially defatted TM meal was included in one of the diets to replace 100%(TM 100)of FM,whereas the other diet(TM 0)was without TM.To analyse the microbial communities,the Illumina MiSeq platform for sequencing of 16S rRNA gene and Qiime pipeline were used to identify bacteria in the gut and skin mucosa,and in the diets.Results:The data showed no major effects of full FM substitution with TM meal on bacterial species richness and diversity in both,gut mucosa-and skin mucus-associated microbiome.Skin microbiome was dominated by phylum Proteobacteria and especially by Gammaproteobacteria class that constituted approximately half of the bacterial taxa found.The two dietary fish groups did not display distinctive features,except for a decrease in the relative abundance of Deefgea genus(family Neisseriaceae)in trout fed with insect meal.The metagenomic analysis of the gut mucosa indicated that Tenericutes was the most abundant phylum,regardless of the diet.Specifically,within this phylum,the Mollicutes,mainly represented by Mycoplasmataceae family,were the dominant class.However,we observed only a weak dietary modulation of intestinal bacterial communities.The only changes due to full FM replacement with TM meal were a decreased number of Proteobacteria and a reduced number of taxa assigned to Ruminococcaceae and Neisseriaceae families.Conclusions:The data demonstrated that TM larvae meal is a valid alternative animal protein to replace FM in the aquafeeds.Only slight gut and skin microbiota changes occurred in rainbow trout after total FM replacement with insect meal.The mapping of the trout skin microbiota represents a novel contribution of the present study.Indeed,in contrast to the increasing knowledge on gut microbiota,the skin microbiota of major farmed fish species remains largely unmapped but it deserves thorough consideration.

GFAP expression in the optic nerve and increased Н2S generation in the integration centers of the rainbow trout（Oncorhynchus mykiss） brain after unilateral eye injury

Hydrogen sulfide(H2S)is considered as a protective factor against cardiovascular disorders.However,there are few reports on the effects of H2S in the central nervous system during stress or injury.Previous studies on goldfish have shown that astrocytic response occurs in the damaged and contralateral optic nerves.Glial fibrillary acidic protein(GFAP)concentration in the optic nerves of rainbow trout has not been measured previously.This study further characterized the astrocytic response in the optic nerve and the brain of a rainbow trout(Oncorhynchus mykiss)after unilateral eye injury and estimated the amount of H2S-producing enzyme cystathionineβ-synthase(CBS)in the brain of the rainbow trout.Within 1 week after unilateral eye injury,a protein band corresponding to a molecular weight of 50 kDa was identified in the ipsi-and contralateral optic nerves of the rainbow trout.The concentration of GFAP in the injured optic nerve increased compared to the protein concentration on the contralateral side.The results of a quantitative analysis of GFAP+cell distribution in the contralateral optic nerve showed the largest number of GFAP+cells and fibers in the optic nerve head.In the damaged optic nerve,patterns of GFAP+cell migration and large GFAP+bipolar activated astrocytes were detected at 1 week after unilateral eye injury.The study of H2S-producing system after unilateral eye injury in the rainbow trout was conducted using enzyme-linked immunosorbent assay,western blot analysis,and immunohistochemistry of polyclonal antibodies again st CBS in the integrative centers of the brain:telencephalon,optic tectum,and cerebellum.Enzyme-linked immunosorbent assay results showed a 1.7-fold increase in CBS expression in the rainbow trout brain at 1 week after unilateral eye injury compared with that in intact animals.In the ventricular and subventricular regions of the rainbow trout telencephalon,CBS+radial glia and neuroepithelial cells were identified.After unilateral eye injury,the number of CBS+neuroepithelial cells in the pallial and subpallial periventricular regions of the telencephalon increased.In the optic tectum,unilateral eye injury led to an increase in CBS expression in radial glial cells;simultaneously,the number of CBS+neuroepithelial cells decreased in intact animals.In the cerebellum of the rainbow trout,neuroglial interrelationships were revealed,where H2S was released,apparently,from astrocyte-like cells.The organization of H2S-producing cell complexes suggests that,the amount of glutamate produced in the rainbow trout cerebellum and its reuptake was controlled by astrocyte-like cells,reducing its excitotoxicity.In the dorsal matrix zone and granular eminences of the rainbow trout cerebellum,CBS was expressed in neuroepithelial cells.After unilateral eye injury,the level of CBS activity increased in all parts of the cerebellum.An increase in the number of H2S-producing cells was a response to oxidative stress after unilateral eye injury,and the overproduction of H2S in the cerebellum occurred to neutralize reactive oxygen species,providing the cells of the rainbow trout cerebellum with a protective effect.A structural reorganization in the dorsal matrix zone,associated with the appearance of an additional CBS+apical zone,and a decrease in the enzyme activity in the dorsal matrix zone,was revealed in the zones of constitutive neurogenesis.All experiments were approved by the Commission on Biomedical Ethics,A.V.Zhirmunsky National Scientific Center of Marine Biology(NSCMB),Far Eastern Branch,Russian Academy of Science(FEB RAS)(approval No.1)on July 31,2019.

An Effective Method of Prompting Juvenile Rainbow Trout (Oncorhynchus mykiss) to Cope with Heat Stress

In the present study,juvenile rainbow trout(Oncorhynchus mykiss)were acclimated at 5 temperatures.Fish in the control group(C0)were reared at a constant temperature(16℃);trout in four other treatments(A0,A3,A6,and A9)were acclimated to a high temperature(22℃)for 0,3,6,and 9 d,respectively,and then returned to normal temperature(16℃)for 7d.The temperature was then raised to 20℃and the fish were cultured for 40 d.The results showed that the growth rates of A3,A6,and A9 were higher than that of A0 but lower than that of C0.The growth rate of A9 was the highest among the 4 acclimation groups.The activities of serum transaminase and liver antioxidant enzyme significantly increased during acclimation.At the beginning of growth,the activities of enzymes were lower in A3,A6,and A9 with the lowest in A9.In addition,the transcript abundance of heat shock protein(HSP)60 gene in A9 was not significantly different from that of C0 during growth.HSP70 in A9 significantly increased at the beginning and returned to that of C0 at the end.Our findings indicated that pre-acclimation improved the high temperature tolerance with the best effectiveness observed at 22℃for 9 d.A possible mechanism underlining such phenomenon is the improvement of antioxidant defense system.

Effect of micro-algae Schizochytrium sp.supplementation in plant diet on reproduction of female rainbow trout(Oncorhynchus mykiss):maternal programming impact of progeny

Background:The broodstock diet,and in particular the lipid and fatty acid composition of the diet,is known to play a key role in reproductive efficiency and survival of the progeny in fish.A major problem when replacing both fish meal and fish oil by plant sources is the lack of n-3 long chain polyunsaturated fatty acids,such as eicosapentaenoic acid(EPA)and docosahexaenoic acid(DHA).To address this problem,we studied the effect of the plant-based diet supplemented with Schizochytrium sp.microalgae,source of DHA,compared to a conventional commercial diet rich in fish meal and fish oil on reproductive performance and egg quality and the consequences on progeny,in female rainbow trout broodstock.Results:The results demonstrated that DHA-rich microalgae supplementation in a plant-based diet allowed for the maintenance of reproductive performance and egg quality comparable to a conventional commercial feed rich in fish meal and fish oil and led to an increased significant fry survival after resorption.Moreover,when females were fed a plant-based diet supplemented with micro-algae,the 4-month-old progenies showed a significant higher growth when they were challenged with a similar diet as broodstock during 1 month.We provide evidence for metabolic programming in which the maternal dietary induced significant protracted effects on lipid metabolism of progeny.Conclusions:The present study demonstrates that supplementation of a plant-based diet with DHA-rich microalgae can be an effective alternative to fish meal and fish oil in rainbow trout broodstock aquafeed.

Effect of Stocking Density on Water Quality and(Growth, Body Composition and Plasma Cortisol Content) Performance of Pen-Reared Rainbow Trout(Oncorhynchus mykiss)

The goal of the study was to examine the effect of stocking density on the water quality of culture area, as well as the growth, body composition and cortisol content of rainbow trout(Oncorhynchus mykiss). Pen-reared trout were stocked in densities of 40, 60, 80 fish individuals m^(-3)(4.6, 6.6, 8.6 kg m^(-3), SD1, SD2 and SD3 groups, respectively) for 300 days. Compared to the water from SD1 and SD2, that from SD3 exhibited significantly higher NH_4^+-N content and COD(chemical-oxygen-demand), and a significant reduction of dissolved oxygen in day 180(40.6 kg m^(-3)). Stocking density was significantly associated with body weight, standard length, VSI(viscerosomatic index), CF(condition factor) and FC(food coefficient) in group SD3, particularly in day 240 and day 300(45 or 49.3 kg m^(-3)). Increased crude fat and decreased crude protein were displayed in high density group when the density reached to 36 kg m^(-3). As a cumulative effect of density-related stress, VSI, CF, FC, moisture, and crude protein content varied over time in each density group(SD1, SD2, and SD3). In summary, trout exhibited a better growth performance in low density(26.3 kg m^(-3)) than those reared in high densities(36 and 45 kg m^(-3)). The results indicate that rainbow trout(114.44 g ± 6.21 g, 19.69 cm ± 0.31 cm) initially stocked in 6.6 or 8.6 kg m^(-3) should be lightened to less than 36 kg m^(-3) after an intensive rearing for 240 days.

Novel Surgical Technique for Acoustic Transmitter Insertion in Rainbow Trout Reduces the Need for Surgical Training

The implantation of acoustic transmitters into the peritoneal cavity of fish is typically performed by experienced surgeons. This study compared the effectiveness of an experienced and inexperienced surgeon performing two different types of transmitter insertion techniques on rainbow trout (Oncorhynchus mykiss). The methods used were either a traditional sutured ventral incision or a novel unsutured lateral incision. There was no significant difference in surgical duration, tag retention, or fish survival between the experienced and naïve surgeon. The time to complete surgical wound closure was not significantly different between the fish operated on by an experienced or naïve surgeon, and surgeon experience had no significant effect on the duration of inflammation. However, there were significant differences between the two surgical techniques, regardless of surgeon experience. The ventral incision with sutures method took approximately three times longer to complete than the lateral incision-only method. However, complete wound closure was significantly faster in the sutured ventral incision treatment compared to the unsutured lateral treatment. Post-surgery inflammation was over seven times longer in the fish with sutures compared to those only receiving a lateral incision. Tag retention was not significantly different between the two surgical methods. The results of this study indicate that the unsutured lateral surgical technique used in this experiment can be completed with minimal training and surgical experience in contrast to the standard technique requiring sutures. These results also provide additional support to the use of sutureless surgical techniques for acoustic transmitter implantation.

Fatty Acid Composition and Digestive Enzyme Activities of Rainbow Trout in Response to Dietary Docosahexaenoic Acid(DHA)and Eicosapentaenoic Acid(EPA)During Salinity Acclimation

This physiological study aimed to evaluate the effects of dietary docosahexaenoic acid(DHA)and eicosapentaenoic acid(EPA)on the fatty acid composition and digestive enzyme activities of rainbow trout(Oncorhynchus mykiss)during salinity acclimation.Rainbow trout with an average initial weight of 90.61 g±9.25 g were fed diets with the quantities of DHA and EPA equaling to 0.54%,0.95%,1.40%and 1.79%(abbreviated as DE-0.54,DE-0.95,DE-1.40,and DE-1.79,respectively)for eight weeks,after which the gastric and intestinal fatty acids composition were analyzed.Subsequently,the fish underwent salinity acclimation.On days 1,4,7,and 14 after the freshwater was replaced by seawater and at the end of the 8-week period,gastric and intestinal digestive enzyme activities were determined.The results showed that the gastric and intestinal DHA and EPA contents of the fish were positively correlated to their dietary DHA and EPA levels.Low dietary DHA and EPA levels inhibited the protease activity of rainbow trout.Fish in the DE-0.54 group increased the lipase activity to enhance the utilization of lipids maybe due to the inadequate essential fatty acids for fish in this group.Hence,rainbow trout in the DE-0.54 group failed to maintain suitable activities of digestive enzymes after salinity acclimation.Therefore,a diet with minimum 0.95%DHA and EPA levels is necessary for rainbow trout during salinity acclimation.

Difference Analysis of Liver Metabolic Response Between Diploid and Triploid Rainbow Trout Oncorhynchus mykiss Under Fishing Stress

To elucidate the effects of fishing stress on the liver glucose metabolism of both diploid and triploid female rainbow trouts as well as differences in their stress response,blood and liver tissues were collected from 0 h to 24 h after the fishing stress.Blood indexes,such as the levels of white blood cells and red blood cells,cortisol,glucose and lactic acid,as well as activities of key enzymes of the glucose metabolism in the liver,were measured.Furthermore,the mRNA expressions of glucocorticoid receptors and enzymes related to energy metabolism were assessed.The results showed that fishing stress exerted significant effects on blood physiological and biochemical indexes and liver glucose metabolism.Differences were found between diploid and triploid female rainbow trouts in the liver glucose metabolism pathway,as well as the level and performance during stress.The basic glucose metabolism intensity of the triploid liver was higher than that of the diploid liver;however,the hepatic glycogen reserve was lower in the triploid liver.After fishing stress,triploid trouts entered the immunosuppressive state earlier than diploid trouts.Triploid trouts also showed an earlier and stronger stress reaction than diploid trouts,while their energy allocation ability and immune recovery ability were weaker than those of diploid trouts.These results showed that the regulatory ability of diploid female rainbow trouts in response to fishing stress was better than that of triploid trouts.

Thermal Tempering Does Not Impact Rainbow Trout and Brown Trout Survival

Hatchery-reared fish are frequently adjusted (tempered) to the higher water temperatures present in the water bodies where they are to be stocked. This study was undertaken to determine the necessity of such tempering practices. This study used rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) reared at 11.2°C. The first two trials for each species were designed to simultaneously determine the upper incipient lethal temperature and 100% lethal temperature over a 14-day period. The third trial for each species evaluated the effects of an exaggerated 12-hour tempering regime on fish survival after placement in elevated water temperatures. After transfer from a water temperature of 11.2°C, no rainbow trout survived at 26°C, and only 50% survived at 25°C. No brown trout survived at 22°C and only 50% at 20°C. Survival of rainbow trout was not improved by the 12-hour tempering regime where water temperatures were slowly increased from 11.2°C to either 25°C or 26°C. Similarly, tempering did not improve brown trout survival at either 20°C or 22°C. These results suggest that tempering is not needed when hatchery-reared trout are reared and stocked at the water temperatures within the range of those used in this study.

Sutureless Implantation of Acoustic Transmitters in Rainbow Trout Exceeding 2% Tag-to-Body Ratio

A novel sutureless surgical technique has been successfully used to implant acoustic transmitters in relatively large rainbow trout Oncorhynchus mykiss with a tag-to-body-ratio of 0.88%. This study examined the same technique in smaller rainbow trout in two, 12-week trials comparing both sutured and sutureless surgical techniques. In the first trial using a tag-to-body-ratio of 1.9% ± 0.04%, tag retention was only 16.6% in fish without sutures, which was significantly lower than the 83.3% retention with sutured incisions. Similarly, in the second trial with a tag-to-body-ratio of 3.2% ± 0.03%, tag retention was 55.5% without sutures, which was significantly lower than the 90.0% retention using sutures. Mortality was not significantly different between treatments in either trial. The results of this study indicate that sutures must be used during surgeries to implant acoustic transmitters in relatively smaller fish with tag-to-body-ratios at or above 1.9%.

Correlation between Leukocyte Numbers and Body Size of Rainbow Trout

Immune cells in rainbow trout Oncorhynchus mykiss comprise granulocytes (neutrophils, basophils and eosinophils), macrophages/monocytes and lymphocytes (B- and T-cells). These cellular elements occur early during the ontogenetic development of trout and allow both innate and adaptive responses towards an antigen to be initiated even in fry. The number of leukocytes in individual fish at different developmental stages is likely to influence the capacity of the fish to respond simultaneously to several antigens (pathogens and vaccine components). This parameter may therefore be crucial for both wild and cultured fish and we show that the size of the leukocyte population increase exponentially with body size of rainbow trout. Four groups (5 fish/ group) of naive rainbow trout (Oncorhynchus mykiss) with a mean body weight of 2-4 g (group I), 4-6 g (group II), 25-30 g (group III), and 650-780 g (group IV) were investigated. The number of lymphocytes was generally higher in head kidney compared to blood and spleen but they dominated in all samples (blood, head kidney, and spleen) and their numbers increased exponentially with fish size. Percentages of lymphocytes in relation to neutrophils and macrophages were higher in spleen (98%-99%) compared to blood and head kidney in all groups. Fish fry is therefore equipped to respond specifically against one or a few vaccine antigens but the capacity to raise protective responses against a repertoire of pathogens may be limited until the larger fingerling stage has been reached. The implications for vaccination of early fry are discussed.

Evaluation of Growth Performance of a Genetically Characterized F1 Rainbow Trout,Oncorhynchus mykiss in a Recirculating Aquaculture System

The growth performance of a selected F1 rainbow trout genetically characterized as polymorphic with locus Omy207UoG (NA = 13, PIC = 0.891, HE = 0.9003) was evaluated in a recirculating aquaculture system (RAS). A set of 157 rainbow trout of 37.8 g of mean body weight and 14.6 cm mean total length per tank, were introduced in each of six fish tank of 5 m3 connected to a recirculating aquaculture system (RAS). The trout was rearing during 317 days. Growth performance indicators and water quality were evaluated during the experiment. The genetically selected F1 rainbow trout showed a tendency towards homogeneity in growth performance along the culture period, reaching a mean total weight of 552.2 g. The length-weight relationship indicated an isometric growth (>3.0). This study presents the basis to establish a long-term marker-assisted selection program for rainbow trout culture in a subtropical region.

Immune response,stress resistance and bacterial challenge in juvenile rainbow trouts Oncorhynchus mykiss fed diets containing chitosan-oligosaccharides

Effects of dietary supplementation of chitosan-oligosaccharides(COS)on the growth performance,immune response,stress resistance,and disease resistance of juvenile rainbow trout Oncorhynchus mykiss were studied.Four experimental diets containing 0,20,40,or 60 mg/kg COS(COS0,COS20,COS40,and COS60,respectively)were fed to juvenile rainbow trout(initial weight=5.2±0.3 g)for 8 weeks.By the end of the feeding trial,representative groups of fish from each dietary treatment were challenged with stressor(30 sec air exposure)and pathogen exposure(intraperitoneal injection with Aeromonas hydrophila).Results showed that supplementation of COS in diets did not affect production performance and body composition of rainbow trout.However,fish fed the COS40 diet demonstrated improved phagocytic activities,respiratory burst activities and decreased serum cortisol level.Additionally,survival following A.hydrophila challenge was significant higher among fish fed the COS-supplemented feeds,although there was no difference based on the level of supplementation.The present study suggests that COS can be used as an immuno-stimulant in rainbow trout feeds.

An initial investigation replacing fish meal with a commercial fermented soybean meal product in the diets of juvenile rainbow trout

The inclusion of PepSoyGen (PSG), a commercially-available fermented soybean meal product, was evaluated with juvenile rainbow trout, Oncorhynchus mykiss in an initial 70-day feeding trial, with a supplemental trial involving a subset of the experimental diets continuing for an additional 40 d. Six diets containing 0%, 10%, 20%, 30%, 40%, or 50% PSG, with the PSG directly replacing fish meal, were used in the first trial. There were no significant differences in weight gain or feed conversion ratio between the fish meal-based control diet and diets containing up to 30% PSG. However, weight gain was significantly reduced and feed conversion ratio significantly increased with the 40% and 50% PSG diets. No health assessment differences were observed in fish receiving any of the diets, and no evidence of gross gut inflammation was evident. There were no significant differences in weight gain or feed conversion ratio among the four dietary treatments ranging from 0% to 30% PSG which were fed for an additional 40 d after the initial 70-d trial (110 days total). Based on these results, juvenile rainbow trout diets can contain up to 30% PSG without any loss of rearing performance, thereby replacing at least 60% of the fish meal.

ANNUAL CHANGES IN PLASMA LEVELS OF CORTISOL AND SEX STEROID HORMONES IN MALE RAINBOW TROUT, ONCORHYNCHUS MYKISS

The profiles of cortisol, testosterone, 11 ketotestosterone and 17α, 20β dihydroxy 4 pregnene 3 one in male rainbow trout reared under constant water temperature and natural photoperiod were determined by radioimmunoassay. Gonads of male rainbow trout reached maturity when the fish were two years old. Changes in the plasma levels of both sex steroid hormones and cortisol were closely related to the GSI. Plasma levels of testosterone, 11 ketotestosterone and 17α, 20β dihydroxy 4 pregnene 3 one showed a clear peak in the annual breeding season, when the GSI reached their maxima. Plasma cortisol levels also showed clearly seasonal changes in both two and three year old fish. The results suggest that the elevated plasma levels of cortisol may not just be due to stresses during the breeding season but have certain physiological functions in the reproduction of rainbow trout.

Neurolin expression in the optic nerve and immunoreactivity of Pax6-positive niches in the brain of rainbow trout(Oncorhynchus mykiss) after unilateral eye injury

In contrast to astrocytes in mammals, fish astrocytes promote axon regeneration after brain injury and actively participate in the regeneration process. Neurolin, a regeneration-associated, Zn8-labeled protein, is involved in the repair of damaged optic nerve in goldfish. At 1 week after unilateral eye injury, the expression of neurolin in the optic nerve and chiasm, and the expression of Pax6 that influences nervous system development in various brain regions in the rainbow trout(Oncorhynchus mykiss) were detected. Immunohistochemical staining revealed that the number of Zn8+ cells in the optic nerve head and intraorbital segment was obviously increased, and the increase in Zn8^+ cells was also observed in the proximal and distal parts of injured optic nerve. This suggests that Zn8^+ astrocytes participate in optic nerve regeneration. ELISA results revealed that Pax6 protein increased obviously at 1 week post-injury. Immunohistochemical staining revealed the appearance of Pax6^+ neurogenic niches and a larger number of neural precursor cells, which are mainly from Pax6^+ radial glia cells, in the nuclei of the diencephalon and optic tectum of rainbow trout(Oncorhynchus mykiss). Taken together, unilateral eye injury can cause optic nerve reaction, and the formation of neurogenic niches is likely a compensation phenomenon during the repair process of optic nerve injury in rainbow trout(Oncorhynchus mykiss).

Influence of Maternal and Larval Immunisation against <i>Lactococcus garviae</i>Infection in Rainbow Trout <i>Oncorhynchus mykiss</i>(Walaum) Lysozyme Activity and IgM Level

This study evaluated efficacy of maternal and larval immunisation against Lactococcus garviae infection and on the lysozyme and immunoglobulin (IgM) levels in rainbow trout Oncorhynchus mykiss (Walaum). Forty-eight-day-old larvae (mean weight 96 mg) originating from injected weekly with letrozole and immunised, only immunised and non-immunised parents were experimentally infected with the L. garvieae, and the mortality rate was recorded daily. Larvae were vaccinated by immersion at 58 days post hatch with live L. garvieae (109 cells/mL) for 15 min. Every third day post larvae vaccination, two larvae from each group were collected for analysis lysozyme (by a method based on the ability of lysozyme to lyse the bacterium Micrococcus lysodeikticus) and IgM (by enzyme-linked immunosorbent assay (ELISA)) parameters. Vaccinated and control larvae were tested for protection against L. garvieae 30 days post larvae immunization when the larvae were 88 days old. Larvae were challenged by bath exposure with live L. garvieae (109 cells/mL) for 2 min and monitored for mortality for at least 10 days following challenge. The challenge experiment with L. garvieae showed a significant reduction in larvae from immunised (54.44% ± 0.64%) and injected weekly with letrozole and immunised fish (52.96% ± 0.97%) compared to larvae from control fish (62.96% ± 2.22%). Vaccinated larvae originated from injected weekly with letrozole and immunised parents showed significantly higher lysozyme activity compared to other fish groups. Vaccinated larvae showed significantly less mortality compared to controls. The relative percent survival (RPS) values of larvae from only immunised, injected weekly with letrozole and immunised and non-immunised parents vaccinated with L. garvieae were 67.36% ± 0.9%, 68.05% ± 0.66% and 48.27% ± 2.79% respectively. The results indicate that the effect of maternal immunization rainbow trout against L. garvieae infection by eliciting the immune responses as indicated by an increase in the IgM level and lysozyme activity.

Effects of varying densities on serum reproductive parameters in pen-reared juvenile female rainbow trout Oncorhynchus mykiss farms

The primary goal of this study was to assess the effect of varying densities on serum reproductive parameters of immature rainbow trout Oncorhynchus mykiss. Experimental trout were maintained in intensive, pen-reared farms for 300 days in fresh water reservoirs. Initial densities were 4.6, 6.6, and 8.6 kg/m^3(40, 60, 80 ind./m^3), indicated as SD1, SD2, SD3, and final densities were 31.1, 40.6, 49.3 kg/m^3, respectively. A summary of the ovarian stages were observed by histological examination. Serum E 2(estradiol), T(testosterone) were evaluated by radioimmunoassay and FSH(follicle-stimulatinghormone), LH(luteinizing-hormone), vitellogenin, 17α,20β-P(17α,20βdihydroxy4-pregnen-3-one) were measured by enzyme-linked immunosorbent assay. Our findings demonstrated that ovarian development were retarded(from stage Ⅲ to stage Ⅳ) at highest rearing density(SD3) after 180 days of intensive culture(over 40.6 kg/m^3). In addition, we observed an inverse relationship between serum reproductive parameters and rearing density. Furthermore, compared to serum reproductive parameters of SD1, E 2, T, FSH, vitellogenin, 17α,20β-P, GSI and LH of two higher density groups decreased firstly and significantly at 60(over 15.9 kg/m^3), 180(over 31.7 kg/m^3), 180(over 40.6 kg/m^3), 240(over 36 kg/m^3), 240(over 36 kg/m^3), 240(over 45 kg/m^3) and 300(over 49.3 kg/m^3) days, respectively. Comparing serum reproductive parameters within the same ovarian development stage of rainbow trout from varying densities revealed that higher population density also led to significantly lower overall serum reproductive parameters. Overall, this study presents the reproductive, endocrinological parameters of juvenile female rainbow trout at high rearing densities and indicates the need for rainbow trout(114.44±5.21 g, 19.69±0.31 cm) that are initially stocked at 6.6 or 8.6 kg/m^3 should be classified and subdivided into lower density after 180 days of farming(not over 31.7 kg/m^3).