Masashi Maita

Modulation of intestinal morphology and immunity in nile tilapia (Oreochromis niloticus) by Lactobacillus rhamnosus GG.

The use of lactic acid bacteria from human origins as a potential probiotic supplementation in aquaculture feed is now widely accepted. Here, we examined some of the properties and mechanisms of the action of Lactobacillus rhamnosus GG, originating from humans, on growth performance, gut mucosal immunity and humoral and cellular immune response in tilapia (Oreochromis niloticus). The results suggested that supplementation of L. rhamnosus gave an advantage in promoting the intestinal structure and the mucosal immunity of tilapia. Probiotic fish had a greater villous height in all parts of the intestines and, significantly, in the proximal and middle part. The population of intraepithelial lymphocytes was significantly higher in the probiotic group than in the control group in all parts of the intestines. The population of acidophilic granulocyte in the probiotic group was significantly higher at the proximal and distal parts when compared with the control group. The higher serum complement activity as well as the enhanced phagocytosis and killing ability of the head kidney leukocytes in the probiotic supplemented fish corresponded with the higher level of TNF alpha and IL-1 gene expression, suggesting that the induction of IL-1 and TNF alpha cytokines by L. rhamnosus served as an important regulator of gut associated immune systems.

Physiological responses during stress and subsequent recovery at different salinities in adult pejerrey Odontesthes bonariensis

Mortality and physiological responses (plasma cortisol, glucose, osmolality, ions Na+ and Cl− and hematocrit values) were examined in adult pejerrey Odontesthes bonariensis subjected to transport or crowding and subsequent recovery for 1 week at 0, 5 and 20 ppt NaCl. Two experiments were conducted using fish from different hatcheries; the following responses were consistent for both stocks. Mortality was observed only during post-stress recovery at 0 and 20 ppt NaCl but not at 5 ppt. During recovery, blood cortisol and glucose were generally higher, whereas osmolality and blood electrolytes (Na+ and Cl−) were lower at 0 ppt than at the other salinities. A salinity of 5 ppt NaCl could not prevent the rise in cortisol and glucose levels caused by the stress of transport, but during recovery, it prevented further increases in these features and/or accelerated their return to basal levels. This salinity also helped maintain stable blood electrolyte levels. During recovery at 20 ppt NaCl, osmolality and blood ions increased, whereas plasma cortisol and glucose generally decreased. Hematocrit values were lower at 20 ppt than at the other salinities. These results suggest that freshwater is not an adequate medium for post-stress recovery and that the presence of NaCl in the water either decreases the secretion of cortisol or promotes its clearance in O. bonariensis.

Disease resistance and hypocholesterolemia in yellowtail Seriola quinqueradiata fed a non-fishmeal diet

The physiology of yellowtail fed a non-fishmeal diet was examined, with a specific interest in the role of taurine in disease resistance and cholesterol metabolism. Decrease of disease resistance in fish fed a non-fishmeal diet was confirmed by mortality due to natural infection with pseudotuberculosis and artificial infection with Lactococcus garvieae. It is suggested that the most important symptoms related to decrease of disease resistance in fish fed a non-fishmeal diet is anemia. Anemia was improved by supple mentation with taurine. Significant elevation of relative expression of HMG-CoA reductase mRNA in fish fed a non-fishmeal diet suggests that cholesterol synthesis would be activated and not dysfunctional. Plasma cholesterol of these fish was elevated to the levels of control fish by supplementation of both cholesterol and taurine. These results suggest that hypocholesterolemia observed in fish fed a non-fishmeal diet compared with a fishmeal diet would be caused by insufficient dietary cholesterol and decrease of endogenous cholesterol due to the lack of dietary taurine.

Epizootics of Erythrocytic Inclusion Body Syndrome in Coho Salmon Cultured in Seawater in Japan

Abstract Epizootics attributable to erythrocyytc inclusion body syndrome (EIBS) occurred among populations of coho salmon Oncorhynchus kisutch cultured in seawater in Japan. Onset of the disease was correlated with water temperatures declining to below 10°C. Symptoms of EIBS were severe anemia with hematocrits of less than 20% and corresponding changes in erythrocyte counts, hemoglobin concentration, and mean corpuscular hemoglobin concentration. Erythrocytes had characteristic inclusion bodies that contained enveloped viral particles with a diameter of approximately 77 nm. The disease was reproduced in artificially induced infections.

The Pathological Effects of Melamine and Cyanuric Acid in the Diet of Walking Catfish (Clarius batrachus)

The toxicity of melamine and its analogue in man and animals has been reported widely. The aim of the present study was to examine the pathological effects of feeding melamine and cyanuric acid, separately or in combination, to walking catfish (Clarius batrachus). The catfish developed darkening of the skin as early as 3 days post feeding. Melamine-related crystals were distributed multifocally throughout the liver, kidney, heart, spleen and corpuscle of Stannius of fish fed melamine and cyanuric acid in combination. Oil red O staining and electron microscopy revealed that the melamine-related crystals had structure resembling that of plastic polymer crystals. Elevations in the serum concentrations of alanine transaminase, aspartate transaminase, creatinine and uric acid were related to the crystal-associated granulomatous inflammation in the liver and kidney of affected fish. None of the catfish died during the 2-week experiment. Melamine and cyanuric acid are therefore systemically toxic to fish in addition to causing renal crystal formation and renal damage as seen in man and animals. The finding of extrarenal crystals implies that the metabolism and biotransformation of these toxic compounds should be further investigated in aquatic animals.

The significance of cortisol on acclimation to salinity in pejerrey Odontesthes bonariensis

Investigou-se a participacao do cortisol na osmoregulacao de peixe-rei Odontesthes bonariensis, em diferentes salinidades, em peixes adultos injetados com 0,7mg hidrocortisona por 100g de peso corporal, e transferidos para 0, 5 e 20ppt de NaCl. No inicio do experimento (0h), o cortisol encontrado no plasma foi de 566ng/ml, aumentando para 1250ng/ml em 3h em peixes injetados com cortisol. A concentracao de cortisol foi influenciada nao somente pelo tratamento, mas tambem pelo tempo, sendo maior 3h apos a inoculacao, comparada a 24h. A salinidade, o tempo de exposicao e a interacao desses dois fatores, mas nao o tratamento com o cortisol, afetaram significativamente a osmolaridade e a concentracao dos ions Cl- e Na+ do plasma. Este estudo mostrou que, o cortisol exogeno nao influi significativamente na regulacao da osmolaridade e da concentracao de ions Na+ e Cl- no plasma em peixe-rei.

Effect of Chinese parsley Coriandrum sativum and chitosan on inhibiting the accumulation of cadmium in cultured rainbow trout Oncorhynchus mykiss

Toxic heavy metals such as cadmium (Cd) accuulate in cultured fish from solid-form feed mixtures. In this paper, two natural ingredients, supposed to inhibit accumulation of heavy metals in the fish body, were investigated to develop a functional feed mixture for healthy fish. Three test diets: (i) #1, regular diet as negative control; (ii) #2, #1 +2% lyophilized Chinese parsley Coriandrum sativum (CP); and (iii) #3, #1 +3% chitosan (CT), were each fed to 50 rainbow trout Oncorhynchus mykiss once a day, at the constantrate of 1.0–1.2% of body weight for 12 weeks. No undesirable effect on fish growth was observed by an addition of either CP or CT to regular feed. Then, 10 mg Cd was added to 1 kg each of the three test diets and they were named as: (i) #4, #1 +Cd; (ii) #5, #2 +Cd; and (iii) #6, #3 +Cd, respectively. The fish given positive a control feed (diet #4) for 3 weeks accumulated Cd in the liver and kidney at approximately 0.52 mg/kg. However, Cd in ordinary muscle was found to be just above the detection limit. Upon accumulation of Cd, three groups of 50 fish were each fed test diets #4, #5, and #6 for 12 weeks at the same feed rate described above. The concentrations of Cd accumulated in the liver, kidney, and ordinary muscle of the fish were measured every 3 weeks. Contrary to the positive control fish fed diet #4, those fish fed test diets #5 and #6 accumulated 20–30% and 25–40% less Cd in the liver, respectively. Test diets were a little less effective for inhibition of Cd uptake in the kidney than that observed in the liver. These results suggest that addition of CP or CT to fish feed might be used to decrease toxic heavy metal accumulation in fish.

Development of a serology-based assay for efficacy evaluation of a lactococcicosis vaccine in Seriola fish

Lactococcicosis is an infection caused by the bacterium Lactococcus garvieae and creates serious economic damage to cultured marine and fresh water fish industries. The use of the assay currently applied to evaluate the potency of the lactococcicosis vaccine is contingent upon meeting specific parameters after statistical analysis of the percent survival of the vaccinated yellowtail or greater amberjack fish after challenge with a virulent strain of L. garvieae. We found that measuring the serological response with a quantitative agglutinating antibody against the L. garvieae antigen (phenotype KG+) was an effective method of monitoring the potency of lactococcicosis vaccines. Vaccinated fish had significantly higher antibody titers than control fish when the L. garvieae Lg2-S strain was used as an antigen. Furthermore, the titer of the KG + agglutinating antibody was correlated with vaccine potency, and the cut-off titer was determined by comparing the data with those from the challenge test. An advantage of the proposed serology-based potency assay is that it will contribute to reduced numbers of animal deaths during vaccine potency evaluations.

Deformation and blemishing of pearls caused by bacteria

Bacteria cause deformation and blemishing in pearls, and we investigate this relationship. We examined pearls derived from Pinctada margaritifera, Pinctada maxima, and Pinctada fucata, and determined the location of bacteria using histopathological and immunohistochemical techniques and 16S ribosomal RNA (rRNA) sequence analyses. The most remarkable change was the inflammatory reaction located between the pearl nucleus and the nacreous layer, composed of hemocytic infiltration with melanization, periostracum, and fibrous aragonite-like structures. These anomalous changes were limited to abnormal sites, and such inflammatory reaction sites are a major factor in the formation of pearl abnormalities. Bacteria were detected from the inflammatory sites and are suspected as the causative agent. Most of these bacteria were anaerobic.

The study on the candidate probiotic properties of encapsulated yeast, Saccharomyces cerevisiae JCM 7255, in Nile Tilapia (Oreochromis niloticus)

Saccharomyces cerevisiae JCM 7255 was tested as a probiotic candidate in tilapia after encapsulating and freeze drying. Viability and morphology during storage and during transit through simulated gut and bile conditions were determined. Growth performance, anti-streptococcal activity and gut mucosal immune parameters were also tested. The viability of encapsulated yeasts was significantly high in simulated gastric and bile conditions and remained high after storage at room temperature for 14 days. The morphology of free S. cerevisiae revealed rough, bumpy, ruptured surface during incubation in gut and bile conditions. Agar spot anti-streptococcal activity showed inhibition of 20 out of 30 strains of Streptococcus agalactiae. Supplementation improved the intestinal structure and growth performance in tilapias. Intraepithelial lymphocytes in the proximal intestine were significantly observed. Lower cumulative mortality after the oral streptococcal challenge was also seen. The results suggest that encapsulated S. cerevisiae JCM 2755 could be a potential probiotic strain in tilapia culture.