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.     

Wheat grains fermented by fungal mycelia (<Emphasis Type="Italic">Pleurotus ostreatus</Emphasis> or <Emphasis Type="Italic">Lentinus edodes</Emphasis>) as alternative feed ingredients for juvenile rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

We investigated the effects of replacing non-fermented wheat grains with wheat grains fermented by fungal mycelia in the diet of juvenile rainbow trout (Oncorhynchus mykiss). We assessed growth performance, feeding parameters, and body composition in three experimental groups (0.33?±?0.01 g, in triplicates of 50 individuals each). The diets for all the groups contained ca. 43% protein and 19% lipids. Experimental diets were made by replacing the 100 g kg^?1 of wheat grains present in the basal diet (CTRL) with the same proportion of wheat grains fermented by Pleurotus ostreatus (PWD) or Lentinus edodes (LWD) mycelium. Fish were fed to apparent satiation twice a day for 56 days. Both, PWD and LWD, significantly increased fish body weight from day 28 onwards. Final body weight was 2.37?±?0.04 g (CTRL), 4.29?±?0.02 g (PWD), and 3.50?±?0.05 g (LWD), and feeding efficiency (%) was increased from 64.5?±?0.7 (CTRL) to 92.5?±?0.5 (PWD) and 84.8?±?1.5 (LWD). The experimental diets also improved nutrient retention efficiency (%): 30.0?±?0.5 (PWD), 27.7?±?1.1 (LWD), and 21.0?±?0.1 (CTRL), for crude protein; 40.3?±?0.6 (PWD), 31.0?±?1.8 (LWD), and 16.1?±?0.7 (CTRL), for ether extract; and 16.1?±?0.1 (PWD), 14.0?±?0.3 (LWD), and 11.6?±?0.6 (CTRL), for phosphorus. Body lipid content was highest for PWD followed by LWD and CTRL (81.4?±?1.4, 63.2?±?2.5, 42.3?±?2.6 g kg^?1, respectively), while viscerosomatic index was lowest for PWD (p?<?0.05). Liver glycogen in LWD and PWD fish (0.62?±?0.10 and 0.21?±?0.08% liver weight) was significantly higher than in CTRL fish (0.05?±?0.01% liver weight). Wheat-mycelium meals appear to be suitable dietary ingredients for improving juvenile rainbow trout growth and nutritional performance. These benefits vary according to the mushroom species used.     

Demographic and competition studies on <Emphasis Type="Italic">Brachionus ibericus</Emphasis> and <Emphasis Type="Italic">Proales similis</Emphasis> in relation to salinity and algal (<Emphasis Type="Italic">Nannochloropsis oculata</Emphasis>) density

We isolated the rotifers Brachionus ibericus and Proales similis from the sediment of shrimp tanks and studied their individual demographic characters and competition between them at two food levels (0.25?×?10⁶, 1.00?×?10⁶ cells ml^?1 of Nannochloropsis oculata at 25 °C) and salinities ranging from 10 to 30‰. Our hypothesis was that growth rates would be higher with increasing food levels and salinities. Observations were taken twice a day for life table studies and daily once for population growth experiments. Using survivorship and fecundity data, we derived various life history variables. Although the average life span (7.6?±?0.4 days) and gross reproductive rate (33.8?±?2.9 neonate female^?1 day^?1) of B. ibericus were higher than those of P. similis (average life span 5.4?±?0.6 days and gross reproductive rate 13.0?±?0.6 neonate female^?1 day^?1), the population growth experiments showed that P. similis had higher r values (0.32?±?0.005 day^?1) than B. ibericus (0.23?±?0.002 day^?1) at 1.0?×?10⁶ cells ml^?1 of N. oculata. The rotifer P. similis was more adversely affected due to the presence of B. ibericus than vice versa. The data are important for developing techniques for a large-scale culture of these rotifers as food in aquaculture.     

Immunogene expression in head kidney and spleen of common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis> L.) following thermal stress and challenge with Gram-negative bacterium, <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis>

To evaluate the effect of thermal and microbial stress on the immune response of common carp (Cyprinus carpio L.), relative mRNA expression level of pro-inflammatory cytokines [tumor necrosis factor alpha (TNF-α) and interleukin (IL)-1β] and other genes related to immune or stress response [inducible nitric oxide synthase (iNOS), heat shock protein 70 (Hsp70), superoxide dismutase one (SOD1), and glucocorticoid receptor (GR)] was measured by quantitative PCR (qPCR). In addition, total protein and total immunoglobulin level in blood plasma of experimental common carp was also assayed. All the above parameters were estimated 24 h post-challenge with Gram-negative bacterium, Aeromonas hydrophila. Common carp (54.89?±?6.90 g) were initially exposed to 20 °C (control group) and 30 °C (thermal stress group) water temperature for 30 days, followed by experimental challenge with 2.29?×?10⁸ colony forming unit/mL (CFU/mL; LD₅₀ dose) of A. hydrophila. Exposure of fish to thermal stress and subsequently challenge with A. hydrophila significantly (P?<?0.05) increases the IL-1β mRNA expression in head kidney and spleen of common carp by ~?39.94 and ~?4.11-fold, respectively. However, TNF-α mRNA expression in spleen decreased ~?5.63-fold in control fish challenged with A. hydrophila. Thermal stress and challenge with bacterium suppresses the iNOS and GR mRNA expression in spleen of common carp. Moreover, significant (P?<?0.05) increase in total protein content of blood plasma (~?43 mg/g) was evident in fish exposed to thermal stress and challenged with A. hydrophila. In conclusion, our study highlights the importance of elevated temperature stress and microbial infection in differential regulation of expression of several immunogenes in common carp.     

Can the polyculture with South American catfish improve the feeding efficiency of rainbow trout culture?

The objective of this study was to determine if the South American catfish (Rhamdia quelen) is suitable to be farmed in polyculture with rainbow trout (Oncorhynchus mykiss) in intensive systems during the juvenile phase to maximize feed efficiency. Juveniles of rainbow trout (3.94?±?0.11 g) and South American catfish (2.07?±?0.04 g) were distributed in 16 tanks (100 L) with continuous water renewal at the density of 50 fish/tank. The experimental design was completely randomized with four treatments (proportions between species) and four replicates. The treatments were 100% trout (100T), 70% trout and 30% catfish (70T30C), 50% trout and 50% catfish (50T50C), and 100% catfish (100C). Fish were fed twice daily with pelleted commercial feed (45% crude protein) during an experimental period of 56 days. No feed was provided for the catfish in polyculture. The weight gained by the trout was higher in polyculture. Fish survival did not differ among the treatments. The average survival of the trout in all tanks was 99.6?±?1.0%, while the survival of the South American catfish was 97.9?±?2.7%. The total feed conversion ratio was lower in the 70T30J treatment, followed by the 100T treatment. Rainbow trout and South American catfish are compatible species for farming together in the first phase of their juvenile development. The different spaces occupied by these species inside tanks probably prevent competition or agonistic behavior. Catfish eat the non-ingested leftover diet from the trout, which improves feed conversion and increases sustainability.     

Increased water temperature altered hemato-biochemical parameters and structure of peripheral erythrocytes in striped catfish <Emphasis Type="Italic">Pangasianodon hypophthalmus</Emphasis>

The increase of water temperature due to global warming is a great concern of aquaculturists and fishery biologists. In the present study, we examined the effects of high temperature on hematological parameters and blood glucose levels in striped catfish, Pangasianodon hypophthalmus exposed to three temperature conditions (28, 32, and 36 °C) for 7 days. Fish were sacrificed at days 1, 3, and 7. Erythroblasts (Ebs), erythrocytic cellular abnormalities (ECA), and erythrocytic nuclear abnormalities (ENA) were assayed using peripheral erythrocytes of the sampled fishes. Hemoglobin (Hb) and red blood cell (RBC) significantly (P?<?0.05) decreased at 36 °C after 3 and 7 days of exposure, whereas white blood cell (WBC) showed opposite scenario. Blood glucose levels significantly (P?<?0.05) increased at 36 °C on day 3. Frequencies of Ebs, ECA, and ENA were found to be elevated at increased temperature. Differential leucocytes count showed significant increases in neutrophil and decreases in lymphocytes in the highest temperature (36 °C). Dissolved oxygen decreased and free CO₂ increased significantly (P?<?0.05) with increasing temperature, while the pH and total alkalinity of the water were almost unchanged throughout the study period. Therefore, the present study demonstrated that striped catfish feel better adaptation at 28 and 32 °C, while high temperature 36 °C is likely stressful to this fish species.     

Changes in the physicochemical and microbiological properties of dried anchovy <Emphasis Type="Italic">Engraulis japonicus</Emphasis> during storage

This study investigated the changes in the pH, thiobarbituric acid (TBA) value, volatile basic nitrogen (VBN), color L*, a*, b*, shear force, and microbial content (total plate count; TPC) of dried anchovy Engraulis japonicus in a home refrigerator and freezer at 2, ??1, ??5, and ??20 °C. The TBA value and shear force significantly decreased with increasing storage duration at all of the tested temperatures (p?<?0.05), whereas the VBN and TPC values increased (VBN significantly so) with increasing storage duration (p?<?0.05). The anchovy L* values decreased, whereas the a* (redness) and b* (yellowness) values increased as the storage period was lengthened. The pH decreased after 9 months. The results suggest that the optimum storage period of the dried anchovy is within 6 months. It can be stored below 2 °C for 3 months, but for storage exceeding 3 months, it should be frozen at ??5 °C.     

Growth and maturation in sterlet <Emphasis Type="Italic">Acipenser ruthenus</Emphasis> under high concentrations of dissolved oxygen

This study investigates the effect of high dissolved oxygen concentrations (DO) on sterlet Acipenser ruthenus maturation. Two groups, each comprising 246 individuals of 8-month-old juvenile sterlets, were reared for 37 months under high DO (group H, mean DO of 11.2 mg/L) or normal DO (group C, mean DO of 7.3 mg/L). Significant differences in body weight were observed between group H (638.7?±?191.9 g) and group C (572.2?±?151.9 g) in 12 months (P?<?0.05). Growth until 12 months occurred at a specific growth rate of 0.6%/day for group H and at 0.5%/day for group C. The food conversion rate of groups H and C was 5.2 and 5.8, respectively. The gonadosomatic index of group H was 3.1?±?1.1 for females and 3.1?±?9.7 for males, and showed no significant difference with group C (3.0?±?0.7 for females and 2.8?±?8.9 for males, P?>?0.05) in 24 months. Significant differences in follicle diameter in mature females were also observed. Group H included 68 mature females, with an average follicle diameter of 2318.0?±?175.3 µm, whereas group C included 56 mature females, with a smaller average follicle diameter of 2152.3?±?287.0 µm (P?<?0.001). However, the polarization index in group H (0.194?±?0.049) was higher than that in group C (0.178?±?0.042) (P?<?0.05). These results suggest that, for sterlet, rearing conditions with high DO can affect growth of both the body and follicle diameter of fish compared to normal rearing conditions.     

Morphology,sex steroid level and gene expression analysis in gonadal sex reversal of triploid female (XXX) rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

In non-mammalian vertebrates, estrogens and expressions of cyp19a1 and foxl2 play critical roles in maintaining ovary differentiation and development, while dmrt1 and sox9 are male-specific genes in testicular differentiation and are highly conserved. In order to deeply understand the morphological change, sex steroids level and molecular mechanism of triploid female gonadal reversal in rainbow trout, we studied the ovary morphology, tendency of estradiol-17β (E2) and testosterone (T) levels and the relative expressions of dmrt1, cyp19a1, sox9 and foxl2 in juvenile and adult fish. Our results demonstrated that the development of triploid female gonads in rainbow trout went through arrested development, oocytes dedifferentiation, ovary reconstruction and sex reversal finally. During early gonadal development (154–334 days post-fertilization), the expressions of foxl2 and cyp19a1 increased linearly, while expressions of dmrt1 and sox9 were extremely suppressed, and E2 level was higher, while T level was lower. During the mid-to-late period of triploid female gonadal development (574–964 days post-fertilization), the expressions of dmrt1 and sox9 remained high and were very close to the quantity of diploid male genes, and T levels were even reaching diploid male plasma concentrations, while expressions of cyp19a1 and foxl2 were decreased, leading to decrease in E2 level. We realized that the development model of rainbow trout triploid female gonads was extremely rare, and the regulatory mechanism was very special. Genes involved in gonadal development and endogenous estrogens are pivotal factors in fish natural sex reversal.     

Immunomodulatory effects of <Emphasis Type="Italic">Rhodomyrtus tomentosa</Emphasis> leaf extract and its derivative compound,rhodomyrtone, on head kidney macrophages of rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

Rhodomyrtus tomentosa is a medicinal plant that shows biological effects including immunomodulatory activity on human and other mammals but not in fish. In this study, we evaluated the in vitro immunomodulatory effects of R. tomentosa leaf extract and its active compound, rhodomyrtone, on the immune responses, using rainbow trout (Oncorhynchus mykiss) head kidney (HK) macrophages as a model. The tested immune functions included the expression of genes involved in innate immune and inflammatory responses and the production of reactive oxygen species (ROS). Gene expression was evaluated after exposure to 10 μg mL^?1 of R. tomentosa and 1 μg mL^?1 of rhodomyrtone for 4 and 24 h. R. tomentosa and rhodomyrtone induced changes in the expression of pro-inflammatory cytokines (il1β, il8, and tnfα), anti-inflammatory cytokines (il10 and tgfβ), inducible enzymes (inos, cox2, and arginase), and an antioxidant enzyme (gpx1). Co-exposure of R. tomentosa with LPS resulted in a prominent reduction in the expression of genes related to an inflammatory process (il1β, il8, tnfα, inos, saa, hepcidin, and gpx1), suggesting anti-inflammatory effects. Similarly, co-exposure of rhodomyrtone with LPS led to a downregulation of inflammation-related genes (il1β, inos, saa, and hepcidin). In addition, exposure to both natural plant products caused a reduction in cellular ROS levels by HK macrophages. The present results indicate that R. tomentosa and rhodomyrtone exerted immunostimulatory and anti-inflammatory effects on fish macrophages, thus opening up the possibility of using these natural products to further develop immunostimulants for health management in aquaculture.     

The effects of starvation on fast-start escape and constant acceleration swimming performance in rose bitterling (<Emphasis Type="Italic">Rhodeus ocellatus</Emphasis>) at two acclimation temperatures

To investigate the effects of starvation and acclimation temperature on the escape ability of juvenile rose bitterling (Rhodeus ocellatus), we measured the fast-start escape and constant acceleration swimming performance of fish fasted for 0 (control), 1 and 2 weeks and half-lethal periods (6 or 4 weeks) at two temperatures (15 and 25 °C). Fish acclimated at a high temperature exhibited shorter response latency (R), higher maximum linear velocity (V _max) and longer escape distance during escape movement (D _120ms) than those at the low temperature. Starvation resulted in a significant decrease in V _max and D _120ms at either low or high temperature and a significant increase in R at only the high temperature in the half-lethal period groups (P < 0.05). The relationship between V _max (Y, m s^?1) and starvation time (X, week) was Y ₁₅ = ?0.062X + 1.568 (r = ?0.665, n = 36, P < 0.001) at low temperature and Y ₂₅ = ?0.091X + 1.755 (r = ?0.391, n = 40, P = 0.013) at high temperature. The relationship between U _cat (Y, cm s^?1) and starvation time (X, week) was Y ₁₅ = ?1.649X + 55.418 (r = ?0.398, n = 34, P = 0.020) at low temperature and Y ₂₅ = ?4.917X + 62.916 (r = ?0.793, n = 33, P < 0.001) at high temperature. The slopes of equations showed a significant difference between low and high temperature (F _1,63 = 9.688, P = 0.003), which may be due to the different energy substrate utilization when faced with food deprivation at different temperatures.     

Differential expression of heat-shock proteins in F2 offspring from F1 hybrids produced between thermally selected and normal rainbow trout strains

Rainbow trout Oncorhynchus mykiss is a cold-water aquaculture species, and a thermally selected strain has been developed by multigenerational high-temperature breeding in Japan. We examined the expression of heat-shock proteins as candidates responsible for thermotolerance in rainbow trout using F2 offspring from F1 hybrids produced between thermally selected and normal strains. From F2 offspring, two groups were selected for western blot analysis, namely, low- and high-thermotolerance groups (times to loss of equilibrium were <30 and ??60?min, respectively). We demonstrated that the expression levels of Hsp70, Hsp60, and Hsp40 in tail fin tissues were significantly higher in the individuals with high thermotolerance than in those with low thermotolerance under non-heat-shock conditions. In particular, Hsp70 was expressed only in the individuals with high thermotolerance. These results suggest that Hsp70 is a major protein responsible for conferring thermotolerance in rainbow trout.     

Effect of dietary chitosan on growth performance,hematological parameters,intestinal histology and stress resistance of Caspian kutum (<Emphasis Type="Italic">Rutilus frisii kutum</Emphasis> Kamenskii, 1901) fingerlings

This study was conducted to investigate the effects of dietary chitosan on growth performance, hematological parameters, intestinal histology, stress resistance and body composition in the Caspian kutum (Rutilus frisii kutum, Kamenskii, 1901) fingerlings. Fish (1.7 ± 0.15 g) were fed diets containing chitosan at different levels (0, 0.25, 0.5, 1 and 2 g kg^?1 diet) for a period of 60 days. Results showed that the feed conversion ratio significantly decreased in fish fed diet containing 1 g kg^?1 of chitosan compared to the other groups (P < 0.05), but there were no significant differences between treatments in terms of specific growth rate and condition factor (P > 0.05). Leukocyte increased in fish fed diet containing 2 g kg^?1 of chitosan compared to the other groups (P < 0.05). Lymphocytes, eosinophils and neutrophils did not significantly change among dietary treatments (P > 0.05). Also, the chitosan supplementation did not affect the whole-fish body composition (P > 0.05). Light microscopy demonstrated that the intestinal villus length increased in fish fed diet containing 1 g kg^?1 of chitosan compared to control group (P < 0.05). While 11 and 13 ‰ salinity and 30 °C thermal stress had no effect, 1 g kg^?1 of chitosan (P < 0.05) showed highest survival rate (70 %) in 34 °C thermal stress. The results showed that chitosan in the diet of the Caspian kutum fingerlings could improve feed conversion ratio, the nonspecific defense mechanisms and resistance to some of the environmental stresses.     

Effects of salinity,stocking density,and algal density on growth and survival of Iwagaki oyster <Emphasis Type="Italic">Crassostrea nippona</Emphasis> larvae

To determine the optimal salinity, stocking density, and algal density for hatchery culture of the Iwagaki oyster Crassostrea nippona larvae, three experiments with salinities of 14, 18, 22, 26, 30, and 34 practical salinity unit (PSU); stocking densities of 0.5, 1, 2, 4, 8, and 12 larvae ml^?1; and algal densities of 10, 20, 40, and 100?×?10³ cells ml^?1 were designed, which included the developmental stages from newly hatched D-larvae to pediveligers. Results showed that larval growth of C. nippona was the fastest at a salinity of 26 PSU, and when salinity was adjusted to a level that was lower or higher than this salinity, survival and growth rate of larvae declined (P <?0.05), resulting both in a decreased mean shell length and a high mortality. Larval growth decreased significantly with increasing stocking density. Larvae reared at 4 larvae ml^?1 had the smallest shell length (198.9 μm) and lowest survival rate (7.9%), whereas larvae reared at 0.5 larvae ml^?1 had the largest shell length (245 μm) and highest survival rate (66.3%) on day 13. And the shell length of larvae reared at 0.5 and 1 larvae ml^?1 was significantly (P?<?0.05) larger than the values in other treatments, except those reared at 2 larvae ml^?1 (P?>?0.05). When feeding the single-algal diet of Isochrysis galbana (clone T-ISO), the shell length of larvae increased markedly as the algal density was increased. Larvae reared at the highest algal density (100?×?10³ cells ml^?1) had the largest mean shell length; however, under the conditions of our experiment, there was no significant difference (P?>?0.05) in growth and survival rates between the treatments at algal densities of 40?×?10³ and 100?×?10³ cells ml^?1. For a large-scale culture, based on the results of this study, a salinity of 26 PSU, stocking density of 0.5–1 larvae ml^?1, and algal density of 40?×?10³ cells ml^?1 are recommended for an early development of C. nippona.     

Effect of stocking density on growth performance,serum biochemical parameters,and muscle texture properties of genetically improved farm tilapia, <Emphasis Type="Italic">Oreochromis niloticus</Emphasis>

The objective of this study was to assess the effects of stocking density on growth performance, serum biochemical parameters, and muscle texture properties of genetically improved farmed tilapia (Oreochromis niloticus, GIFT). Juvenile GIFT with an average initial weight of 12.54?±?0.45 g (mean?±?SD) were randomly stocked in 16 tanks (80 L) in a recirculation aquaculture system at four densities of 10 (D1), 20 (D2), 30 (D3), and 40 (D4) fish per tank for 56 days, with quadruplicate for each density. There were no significant differences in water temperature among the four treatments (P?>?0.05). D4 had the significantly lowest dissolved oxygen content (5.52 vs 5.69–6.09 mg L^?1) (P?>?0.05) and pH (6.63 vs 6.87–7.20) (P?<?0.05). NO₂-N and NH₄-N concentrations significantly increased with increasing stocking density (P?<?0.05). Weight gain (WG) and specific growth rates (SGR) decreased with increasing stocking density. The lowest WG (617.20 vs 660.45–747.06%), SGR (3.52 vs 3.62–3.81% day^?1), and highest feed conversion ratio (1.68 vs 1.53–1.58) were observed in D4. Fish at D4 had significantly lower condition factor (3.11 vs 3.29–3.37%) and survival rate (91.25 vs 97.50%) than those from D1 and D2 (P?<?0.05). With increasing stocking density, serum total cholesterol, triglyceride, and total protein concentrations decreased (P <?0.05) and aspartate aminotransferase and alanine aminotransferase activities increased (P <?0.05). D4 fish had higher moisture content (78.80 vs 76.97%) and lower crude protein content (18.14 vs 19.39%) in muscle than D1 fish (P?<?0.05). Compared to D1 and D2, D3 and D4 had lower muscle hardness (1271.54–1294.07 vs 1465.12–1485.65 g), springiness (0.62–0.65 vs 0.70–0.72), gumminess (857.33–885.32 vs 1058.82–1079.28 g), and chewiness (533.04–577.09 vs 757.53–775.69 g) (P <?0.05). High stocking density resulted in growth inhibition, declines in flesh quality, and disturbance to several serum biochemical parameters.     

Correlation between C-reactive protein level,immunology, and hematology of a <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> infected with <Emphasis Type="Italic">Lactococcus garvieae</Emphasis>

The aim of this experiment was to evaluate the symptoms, variation, and correlation of hematological factors and some parameters of the innate immune response of the infected rainbow trout (Oncorhynchus mykiss) fish with Lactococcus garvieae bacteria. A total of 270 fish were divided into three groups including infected fish with a high and low concentration of L. garvieae and a control group without infection. The blood and tissue (brain, head, kidney, and spleen) samples were collected from each group (n?=?6 fish) at 0, 3, 14, and 21 days after treatment. The most observed symptoms during infection were lethargy, exophthalmia, and ascites. The mortality rates for the high and low dose-infected fish were defined as 60 and 25%, respectively. The infected groups had significantly (p?<?0.05) higher activity of serum lysozyme, myeloperoxidase, classical and alternative pathways of complement, serum bactericidal effects, and the specific antibody titer. Also, a significant (p?<?0.05) lower hematocrit and hemoglobin levels and higher white blood cell numbers were observed in the infected groups. A significant correlation was observed between the CRP levels and some of the hematological and immunological indices as bactericidal effects, classical complement pathways, lysozyme activity myeloperoxidase activity, white blood cell numbers, and hematocrit levels. The clinical symptoms, immune responses, and hematological indices variation among L. garvieae-infected fish are dependent on the duration and bacterial dose of the infection.     

Nitrogen removal characteristics of <Emphasis Type="Italic">Pseudomonas stutzeri</Emphasis> F11 and its application in grass carp culture

This study was designed to investigate the denitrification characteristics of Pseudomonas stutzeri F11 under different environmental conditions and to evaluate the effect of these characteristics on nitrogen removal and the water microbiome in an experimental grass carp aquaculture system. The results showed that the optimal growth conditions of strain F11 were (1) ammonia-nitrogen (N), nitrite-N, or nitrate-N as sole N source; (2) initial ammonia-N concentration of 10–30 mg N/l; (3), initial nitrite-N concentration of 200 mg N/l; (4) sodium citrate as carbon source; (5) rotation (r) speed of 200 r/min; a C:N ratio of between 2 and 10; (6) culture at 32–37 °C. The addition of P. stutzeri F11 to the experimental grass carp aquaculture system reduced the levels of ammonia-N, nitrite-N, and total N in the water over an extended range, but had no effect on nitrate-N level. Results of the 454 pyrosequencing analysis indicated that the structure of the microbial community in the aquaculture water changed significantly after the addition of P. stutzeri F11 preparations. The addition of P. stutzeri F11 to the aquaculture system also altered the microbiome metabolism in the water, especially the bacteria involved in nitrogen metabolism. These results suggest that the addition of P. stutzeri F11 to an experimental grass carp aquaculture system decrease nitrogen levels and alter the microbial community structure of the water; as such, this bacterial strain could be a potential candidate for the regulation of water quality in aquaculture systems.     

Dietary supplementation of yeast (<Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>) improves growth,stress tolerance,and disease resistance in juvenile Nile tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>)

The yeast Saccharomyces cerevisiae is one of the commonest probiotics incorporated in aquafeeds. An 84-day feeding trial was conducted to evaluate the effects of varying dietary inclusions of S. cerevisiae, 0% (control), 3% (YF3), 5% (YF5), and 7% (YF7), on growth, stress tolerance, and disease resistance in juvenile (body mass ~?21 g) Nile tilapia (Oreochromis niloticus). Fish were randomly distributed in groups of 20 into 12 1-m³ hapas and fed isoenergetic (~?17 kJ g^?1 gross energy) and isonitrogenous (~?300 g kg^?1 crude protein) diets at 3% of their bulk weight daily. Specific growth rates were significantly higher for the yeast-fed fish (0.77–0.78% day^?1) than for the control fish (0.60% day^?1) and resulted in significantly higher mean final weights for the yeast-treated groups. Protein and lipid retention efficiencies were also significantly higher in the yeast-fed fish than in the control group. In subsequent stress challenge trials, the yeast-fed fish had greater tolerance to acute heat as well as hypoxia exposure than the control fish. Survival rates of the yeast-treated groups following sudden exposure to elevated water temperature (40 °C) ranged from 82.5 to 100% compared to 15% for the control. Mean survival rates following a 24-h hypoxia exposure were also generally significantly higher for the yeast-fed fish. The probiotic groups recorded a relative percent survival (RPS) of 75% after a 14-day Aeromonas hydrophila infection challenge. The results of this study indicate that S. cerevisiae as an additive in Nile tilapia diets has beneficial impacts on growth, stress tolerance, and disease resistance.