Study of pathogenicity and severity of Lactococcus garvieae isolated from rainbow trout (Oncorhynchus mykiss) farms in Kohkilooieh and Boyerahmad province

Abstract Background Lactococcus garvieae is one of the most important risk factors in the rainbow trout culture. Therefore, the purpose of this study was to identify and detect strains isolated from rainbow trout suspected of having Lactococcus garvieae using biochemical characteristics and PCR and determination of the degree of severity of isolated strains. Methods In this study, the cause of lactococcosis in selected rainbow trout farms in Kohkilooieh and Boyerahmad province was assayed. Gram-positive and catalase-negative bacterial isolates were first obtained from selected trout fish farms using conventional biochemical tests and PCR assay. The 10-day LD50 method (concentration causing 50% mortality in 10 days) was used to determine the severity of the isolated bacteria. Results One bacterial isolate was detected from all sampled fish which confirmed as Lactococcus garvieae using a specific PCR assay based on the 16S rDNA gene by producing a single band of 1107 bp. Analysis of the rate of mortality showed that the 10-day LD50 was 4.6 × 105 CFU/fish. The results of this study showed that isolated bacteria had high severity for rainbow trout. The presence of bacteria in internal organs of suspected fish showed a severe systemic infection in challenged fish. Antibiogram assay also indicated that the isolated Lactococcus garvieae were resistant to some mostly used antibiotics in rainbow trout. Conclusions According to current research, it can be concluded that the condition of lactococcosis in the studied area is not suitable, and despite the presence of disease, there is no proper action to control and prevent the disease. Unfortunately, isolated bacteria from the studied area have a very high severity compared to bacteria isolated from other regions of the country or other countries. Therefore, further investigation is needed to determine the cause of this difference and possibly in the design of the vaccine. </jats:sec

Effects of short-term starvation on biochemical carcass composition, liver glycogen and fat in Silver seabream fingerlings, Sparidentex hasta

Both in nature and in aquaculture, fishes coulde xperience periods of food deprivation or starvation. The present study was investigated the effect of starvation on biochemical body composition, glycogen and fat of liver in Sobaity fingerling. In this study, 300 fingerlings of Sparidentex hasta studied with mean weight 28.47 ± 0.24 g that included four treatments each with three replicates (25 fish per replicate) in a 300-liter polyethylene tanks. Fish of control treatment were fed to saturation twice daily and other treatments of were starved 2, 4 and 8 days. Biochemical composition of liver and carcass were performed at the beginning and end of the period of starvation and samples were transported to the laboratory for analysis . The results of this study showed that 2 days of food deprivation did not affect any of the factors studied (P>0.05), also 4 days of food deprivation was significantly affected on liver glycogen only (P<0.05), but 8 days of food deprivation was significantly effected on liver glycogen, fat and protein of body composition (P<0.05). According to the results of this study it can be stated that; in Sobaity fish, the first priority was the use of liver glycogen stores in food deprivation times; this shows the key role of the liver as the provider of fish body's energy needs, and the next priority was the use of fat and protein stores.Publishe

Pot Marigold (Calendula officinalis) Powder in Rainbow Trout (Oncorhynchus mykiss) Feed: Effects on Growth, Immunity, and Yersinia ruckeri Resistance

The current research investigated the effects of pot marigold (Calendula officinalis) powder on growth, biochemical parameters, digestive enzymes, serum and mucus immune responses, antioxidant defense, and resistance of rainbow trout (Oncorhynchus mykiss) against Yersinia ruckeri. Fish (No. 450, 15.06±0.11 g; mean±SE) were randomly distributed to five groups fed with a diet containing 0 (control group), 0.5%, 1%, 1.5%, and 2% of pot marigold powder (MP) for 60 days. Then, fish were challenged with Y. ruckeri infection. Specific growth rate (SGR), weight gain (WG), final weight (FW), feed conversion ratio (FCR), mucus lysozyme (LYZ), mucus protease, serum nitroblue tetrazolium test (NBT), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) values in the 1%, 1.5%, and 2% MP groups significantly increased (P<0.05) compared to the other groups. Regression analysis exhibited that rainbow trout growth indices were polynomially linked to dietary MP concentrations. In this regard, the optimal levels of MP, according to growth parameters (SGR and FCR), were 1.31 and 1.4% diet, respectively. The intestinal protease, serum complement component 3 (C3), complement component 4 (C4), and LYZ activities in fish fed with the 1% and 1.5% MP-supplemented regime were higher (P<0.05) compared to the other groups. Also, fish fed with diets containing 1.5% MP had significantly higher intestinal lipase and mucus ALP activities than the other groups (P<0.05). Aspartate aminotransferase (AST) activity in all MP groups remarkably increased (P<0.05) compared to the control. Moreover, fish fed with a diet containing 1.5% MP had remarkably higher (P<0.05) lactate dehydrogenase (LDH) and total protein (TP) values than the other groups. Serum myeloperoxidase (MPO), total immunoglobulin (Ig), and mucus peroxidase values in the 1% MP group remarkably increased (P<0.05) compared to the other groups. In addition, catalase (CAT) and superoxide dismutase (SOD) activities in the 1.5% and 2% MP groups were significantly higher (P<0.05) compared to the others. However, malondialdehyde (MDA) levels in fish fed with the 1%, 1.5%, and 2% MP-supplemented diet remarkably decreased than in the other groups (P<0.05). The highest survival rate after a challenge with Y. ruckeri was recorded in the 1.5% group compared to the control group. Our findings revealed that using pot marigold powder in diets, especially at the 1.5% level, has positive effects on growth, digestive enzyme activities, antioxidant capacity, immune response, and disease resistance in O. mykiss