Effects of dietary vitamin B₁ (thiamine) and magnesium on the survival, growth and histological indicators in lake trout (Salvelinus namaycush) juveniles

An interaction of two essential nutrients, thiamine and magnesium (Mg) has been documented in in vitro and in vivo studies in mammalian metabolism. However, the role of this association in poikilothermic vertebrates, such as fish, remains elusive. The purpose of this study was first to investigate the effects of dietary thiamine and Mg, and their interaction in lake trout and second to better understand the mechanism leading to early mortality syndrome (EMS), which is caused by a low thiamine level in embryos of many species of salmonids in the wild. Semi-purified diets (SPD) were prepared to accomplish 2 × 2 factorial design that were either devoid of or supplemented with thiamine mononitrate (20 mg/kg diet), magnesium oxide (700 mg/kg diet), or both. Lake trout alevins at the swim-up stage were fed for 10 wk one of the SPD diets or a commercial diet at the same rate (2.0-1.5%) based on recorded biomass. Our results showed that the concentrations of thiamine in the trunk muscle and Mg of whole body were closely associated with the dietary level of two nutrients. The interaction of low dietary Mg and thiamine resulted in apparently worsened overt symptoms of thiamine deficiency in lake trout leading to a higher mortality of fish during the seven week long trial (P<0.05). The fish fed a thiamine-devoid and Mg-supplemented diet were presumed to survive longer (10 wk) than the fish fed diets devoid of both nutrients (discontinued after 7th wk due to high mortality). However, we did not observe histopathological changes in the brain and liver corresponding to thiamine concentrations in tissues. These data suggest that Mg enhanced utilization of the thiamine remaining in the fish body and its interdependence was consistent with observations in mammals. EMS severity might be worsened when Mg is deficient in parental diets (and consequently in yolk sac) and/or first feed.     

Egg lipid and thiamine vary between early and late spawning lake sturgeon

Nutritional deficiency associated with reduced thiamine (vitamin B1) and reduced natural reproduction of salmonid species in the Great Lake Region is well established. The negative relationship between egg thiamine and lipid concentration to post-hatch larval growth and survival in teleost species, coupled with the limited research of egg thiamine in Acipenseriform species of conservation concern, including lake sturgeon, indicates that study of thiamine concentrations lake sturgeon eggs is warranted. Eggs were collected from females (N = 12) during the early and late portion of the spawning run in 2007 in a wild population from Black Lake, MI. Concentrations of thiamine, lipid and fatty acid concentration were measured along with female biological information (body size and egg size) and characteristics of larvae at hatch. Significant differences in egg thiamine concentrations were observed between early- and late-spawning females (mean ± SD: 2.36 nmol·g⁻¹ ± 1.09 vs. 0.73 ± 0.25 nmol·g⁻¹, W = 0.05, p < .01). No significant relationships were observed between female body size or egg size and egg lipid or thiamine concentration. Differences in lipid and thiamine concentrations were not predictive of larval body size or yolk sac volume at hatch. Total and phosphorylated thiamine were correlated with n-3 polyunsaturated fatty acids, suggesting that dietary items were likely partially responsible for provisioning of essential compounds. Given the negative effects of low egg thiamine concentration on larval survival in other fish species globally, results indicate that further research in areas of nutrient acquisition and thiamine effects on larval survival, natural recruitment, and hatchery feeding strategies is warranted for lake sturgeon.     

Immunoprophylactic effects of shiitake mushroom (Lentinula edodes) against Bordetella bronchiseptica in mice

Antimicrobials are used as feed additives to improve growth performance and to prevent subclinical disease challenge in industrial animals. However, these drugs can lead to the development of resistant strains of bacteria. Shiitake mushrooms (SM) (Lentinula edodes) have long been popular as a health food in East Asia. Moreover, SM-derived polysaccharides are well-known as immunostimulants that possess antimicrobial properties. The aim of the present study was to evaluate the immunoprophylactic effects of SM against Bordetella bronchiseptica infection in mice as an initial step towards the development of eco-friendly feed additives to reduce the use of antimicrobials. Although SM had no effect on body weight gain under the un-infected conditions, SM alleviated progressive weight loss and helped in the recovery of body weight in B. bronchiseptica infected mice. Dietary supplementation with SM reinforced bacterial clearance in the infected mice. Of note, SM markedly increased the percentage of various T lymphocytes and the relative mRNA expression levels of tumor necrosis factor-α and interferon-γ in the bronchial lymph node early in the infection. Taken together, these findings suggest that SM could help in the improvement of body weight gain during B. bronchiseptica infection and may enhance the protective immune activity against a subclinical disease challenge, such as B. bronchiseptica infection in mice, probably by a strong stimulation of non-specific immune responses. Hence, SM may provide an alternative to reduce use of antimicrobials. Confirmation of the beneficial effects of SM as a feed additive is now required in industrial animals.     

Bacterial Communities in Ground-and Surface Water Mixing Zone Induced by Seasonal Heavy Extraction of Groundwater

The water curtain (WC) system has been applied to the greenhouse agricultural practice as an additional heat source during the cold season in South Korea. Thus, heavy groundwater extraction induces a drawdown of the groundwater level and an influx of adjacent surface water into the aquifers. Along with many reports on physicochemical transitions caused by groundwater–surface water mixing, not much knowledge exists about the resulting possible shifts and/or transitions of the subsurface and/or groundwater microbial community structures. Here, we studied a WC system's active site during a winter season to evaluate potential shifts of microbial community structures across the groundwater and surface water by next generation sequencing in combination with conventional physicochemical monitoring of groundwater. We found that there were shifts of groundwater microbial communities at groundwater (WJ-1 and WJ-2) near the adjacent stream, but there was a relatively delayed response of the community in the groundwater (WJ-3) located at some distance from surface water despite proximity to the wells of heavy groundwater extraction.     

Probiotic Potential of the Farmed Olive Flounder,Paralichthys olivaceus,Autochthonous Gut Microbiota

In recent years, considerable and growing attention has been given to the application of host-associated microorganisms as a more suitable source of probiotics in aquaculture sector. Herein, we isolated and screened the olive flounder gut microbiota for beneficial bacterial strains that might serve as potential probiotics in a low fishmeal extruded aquafeed. Among the ten identified isolates, Bacillus amyloliquefaciens SK4079 and B. subtilis SK4082 were screened out based on their heat-resistant ability as well as enzymatic and non-hemolytic activities. Although both strains were well able to utilize carboxymethyl cellulose (CMC), xylan, and soybean meal (SBM) as a single carbon source in the minimal nutrient M9 medium, B. subtilis exhibited significantly higher cellulase, xylanase, and protease activities than B. amyloliquefaciens. The two selected strains were well able to degrade the undesirable anti-nutritional component of the SBM, which would limit its utilization as protein source in aquafeed industry. Significantly higher biofilm formation capacity and notably stronger adhesive interactions with the flounder’s skin mucus were detected in B. subtilis than B. amyloliquefaciens. Immobilization of the spores from the selected strains, in a SBM complex carrier, remarkably enhances their thermal resistance at 120 °C for 5 min and different drying conditions. It was also interesting to learn that the B. subtilis spores could survive and remain viable after being sprayed onto extruded low-fish meal feed pellets for as long as 6 months. Overall, the findings of the present study could help the food/feed industries achieve their goal of developing cost-effective yet efficient products.

     

Effects of vitamin B1 (thiamine) deficiency in lake trout (Salvelinus namaycush) alevins at hatching stage

The objectives of this study were to examine the relationship between thiamine concentrations in unfertilized eggs and yolksac individuals of lake trout (Salvelinus namaycush), along with any associated histopathological changes in the tissues of alevins at the hatching stage. We address these questions in a lake trout population from different spawning grounds of Lake Michigan (North and South), known for compromised survival due to early mortality syndrome (EMS). However, a dichotomous forage base of lake trout spawning stocks, with a dietary thiaminase-rich alewife in the North, and dietary low-thiaminase round goby in the South, provides the basis for the assumption that different diets may lead to differences in severity of EMS between different stocks. Lake trout eggs of 18 females were collected and fertilized individually with the sperm of several males. The eggs, eyed embryos and newly-hatched alevins were sampled to examine thiamine utilization during embryogenesis. Progenies of females with low (< 0.73 nmol/g) and high (> 0.85 nmol/g) levels of thiamine were chosen for histological studies. The obtained results showed that total thiamine levels in the body and yolk of eyed embryos and alevins at hatching were influenced by thiamine levels of unfertilized eggs and it decreased during embryogenesis (to 51% in eyed embryos and 28% in newly-hatched alevins in comparison to unfertilized eggs). The survival of lake trout until hatching stage does not correlate with the thiamine level, however it was affected by collection site and was significantly higher in fish from the South site (Julian's Reef). At the hatching stage, no pathological changes were observed in the brain, olfactory lobe, retina or liver in embryos regardless of thiamine concentrations in unfertilized eggs. It has been concluded that an enhanced thiamine requirement for the fast muscle mass growth near the swim-up stage is responsible for overt and histopathological signs of EMS. Current study confirms earlier findings that lake trout suffering from EMS can be successfully treated by immersion in thiamine solution as late as at the swim-up stage.