Aetiologic Agents of Fry Mortality Syndrome in the Rainbow Trout (Oncorhynchus Mykiss) in Iran

An investigation was conducted in order to find out the etiological factors of Fry Mortality Syndrome (FMS) that causes serious economical loss in rainbow trout farms in Iran. In recent years obscure fry mortalities have been observed in many hatchery farms in Iran. It was reported that the rate of fry and juvenile mortality increased dramatically in some provinces e.g. 23 million fry were produced in hatchery centers of Chahar Mohal Bakhtiary province in 2002 but nearly 21 million fry (91.3%) in different stages of growth died before distribution to farmers. Also close to 23 million fry were produced in Mazandaran province, but 12 million fry equivalent to 52.12% of total fry production died mysteriously.This investigation was carried out with objectives of detecting and confirming the main causative agent that contribute to the occurrence of Fry Mortality Syndrome in Iran. During 32 months, from October of 2001 until May of 2004, 52 different hatchery centers and rearing farms of rainbow trout (Oncorhynchus mykiss) which were located in Tehran, Mazandaran, Guilan, Fras, Markazi, Kerman and Kohkiloyeh Boyerahmad provinces, were visited and various samples from affected farms were collected. Collected samples consisted of ovarian fluid, milts, eggs, eyed-eggs, larvae, fry < 1 g and 1-3 g as well as internal organs from adult fishes. A total of 2,107 samples were collected from farms in six provinces and were examined by five methods such as virology (410 samples), bacteriology (899 samples), serology (consisted of IFAT: 392 samples and ELISA: 44 samples), histopathology (160 samples) and hematology (202 samples). Some of the mentioned approaches such as fish cell culture, ELISA and IFAT techniques were set-up and optimized for the first time in Iran. The clinical signs of suspected fishes were darkening, exophthalmia, ascites, abnormal swimming and whirling. From 410 samples that of tissues inoculated on to cell cultures two samples showed CPE in EPC and BF-2 cell lines which were inoculated with ovarian fluid from broodstock obtained from hatchery farms in Mazandaran province. The CPE was similar to IHN virus induced. The CPE foci revealed dying cells congegrated as grape-like clusters (ballony performance with cytolysis).TEM findings in infected cells showed bullet-shaped particles having sizes of 130-180 nm in length and 65-70 nm in diameter. From the virion morphology it was suggested that observed particles were similar to Rhabdovirus. FAT examination revealed that all samples were examined with MAbs and PAbs against IPNV and VHSV were negative. On the other hand, two samples were positive when examined with MAbs and PAbs against IHNV. These smears were originated from samples that had showed CPE in EPC and BF-2 cell lines and bullet shaped particles in electron microscopy. ELISA findings (cut-off value, optical density and detectionlevel percentage) showed that IHNV had higher percentage of detection with 23.25% in comparison with other relevant viral diseases i.e. IPNV with 7.31% and VHSV with 14.29%. Results of histopathological study on the sampled fry revealed that the target tissues in the kidney, liver, spleen, hepatopancreas, intestine and gills showed different degree of tissue changes beginning from cell degeneration to complete necrosis. There were also renal blood vessels congestion, marked degenerative changes in posterior kidney with tubular necrosis and interstitial hematopoeitic tissue degeneration. In addition, interstitial degeneration and oedema in anterior portion of kidney, focal necrosis in the tubular area and several stages of cell necrosis in the hematopoeitic tissue were the most important histopathological changes seen in kidney tissues examined. Hepatopancreatic tissues also revealed marked changes such as congestion, atrophy and necrosis of pancreatic acinar cells and Islets of Langerhans. Spleen samples revealed spleenic congestion, severe necrosis, hemosiderosis and increased presence of melanomacrophage centers (MMC). Gills tissue in sampled fry showed hyperplasia, clubbing and fusion of lamellae. Hematological findings revealed that total white blood cell count, i.e. lymphocyte and neutrophil in investigated fish showed significant increased compared with the control fish (p< 0.05). On the contrary, all the samples showed a decreased in RBC, Hb and HCT values. In addition, MCHC and total protein plasma showed a marked decreased (p<0.05). In the blood serum components analysis, similarly it was revealed LDH and AST showed a significant decreased (p<0.05). In conclusion, with marked clinical signs, cell culture observation and TEM findings, ELISA and IFAT results, histopathology and hematological findings (blood and biochemical parameters) seen in the current investigation lead to possibility of a viral disease agent infection as the cause of fry mortality syndrome in the hatchery and rearing trout farms in Iran. From findings of the current study, it is concluded that IHN-like virus could be most probable etiologic of fry mortality syndrome in Iran. Key words: Fry Mortality Syndrome, Rainbow trout, Cell culture, TEM, ELISA, IFAT, Histopathology, Hematology, IHNV, IPNV, VHSV, Ira

Vacuolating encephalopathy and retinopathy associated with a nodavirus-like agent: a probable cause of mass mortality of wild Golden grey mullet (Liza aurata) and Sharpnose grey mullet (Liza saliens) in Iranian waters of the Caspian Sea

Mullets are dominant fishes in the catch composition in the southern coasts of the Caspian Sea and after (Rutilus frisii kutum Kamensky, 1901) have a worthy role in production of marine proteins and incomings of north provinces of Iran. Mullets stocks decreased dramatically in recent decades in the Caspian Sea and catch amount reached from 6446 MT on 2002 to 2151 MT in 2012. Mysterious mortalities occurred in wild mullet (Liza auratu) and (Liza saliens) in Iranian waters of Caspian Sea in recent years. Regarding to investigation of causative agent of mentioned outbreak about 322 suspected samples were collected from coastal capture sites of Iranian north provinces in 2008 till 2011. Moribund fish revealed skin darkening, erratic swimming, belly-up at rest and high distension of swim bladder. Target tissues such as brain and eye were removed and then fixed for histopathology and TEM assay. Widespread and massive vacuolation were observed in brain, spinal cord, retina and optical nerve and intracytoplasmic vacuoles and virus particles in retina. So concerning to clinical signs, histopathological and TEM findings, it could be concluded that nodavirus-like agent could be probable cause of mass mortality of wild mullet in Iranian waters of the Caspian Sea

A survey of the functional, gut digestive, and serum antioxidant factors in Salmo trutta caspius (Kessler) fingerlings with the application of a dietary synbiotic

This study evaluated the effectiveness of BetaPlus® combined with isomalto-oligosaccharide (IMO) in Caspian brown trout, Salmo trutta caspius (Kessler), fingerlings. A total of 120 Caspian brown trout (8.75 ± 0.03 g) were fed in two treatments, including the control diet and the synbiotic diet (0.1% BetaPlus® + 0.2% IMO) in three replicates per treatment for seven weeks. The growth indices (final weight, weight gain, average daily growth, specific growth rate, feed efficiency, and protein efficiency ratio) exhibited significant improvement in the fish fed the synbiotic diet (P < 0.05). The highest ash crude protein, and crude fiber, as well as the lowest crude lipid, dry matter, and carbohydrate detected in the carcass of fish treated with the synbiotic were significant (P < 0.05). In addition, the fish fed the synbiotic diet showed significantly higher gut trypsin activity and trypsin:chymotrypsin ratio, as well as serum superoxide dismutase activity (P < 0.05). Thus, BetaPlus® in combination with IMO can effectively lead to a considerable increase in functional factors, as well as gut proteases and serum antioxidant indicators in S. trutta caspius fingerlings

Pathogenicity of viral nervous necrosis virus for Guppy fish, Poecilia reticulata

The pathogenicity of a Nervous Necrosis Virus isolate obtained from naturally infected Golden grey mullet (Liza auratus) suffering serious mortalities in Iranian coastline water of the Caspian Sea was investigated for first time. An experimental infection has been performed using three groups, two experimental groups and one control group of Guppy (Poecilia reticulata) with mean weight 0.47±0.09 g, at temperature 25°C. The infectious dosage (50 ml) with TCID50/ml=104.25 for 2 hours in group 1 and 4 hours in group 2 developed the disease with immersion method. Clear clinical signs associated with significant mortality were observed since 15 dpi. Cumulative mortalities rose to 100% at 30 dpi. While in the control group no mortality was recorded. Virus was re-isolated on SSN-1 cell line that showing typical CPE developed after inoculation with tissues filtrate from dead fish. Histopathological examination of exposed fish, showed clear vacuolization in the granular layer of the retina and cerebellum. TEM micrographs revealed intracytoplasmic vacuoles in the retina of infected Guppy. IHC revealed the presence of viral antigens in the brain and retina. These results confirmed the pathogenicity of the NNV isolate obtained from Golden grey mullet suffering high mortality with regard to suggest that the same agent isolated from golden grey mullet is very likely the cause of the mortality observed in the same species

Zoonotic diseases of fish and their prevention and control

Fish and aquatic-derived zoonotic diseases have caused considerable problems in the aquaculture industry and fishery worldwide. In particular, zoonotic diseases can pose widespread threats to humans. With the world’s growing population and potential global trade of aquaculture and fish, the risk of environmental contamination and development of fish and aquatic-derived zoonoses in humans are increasing. The important causes of zoonoses include bacteria, parasites, viruses, and fungi. The zoonotic bacterial agents are divided into two main groups: Gram-positive (Mycobacteriaceae, Streptococcaceae, Erysipelothricaceae families) and Gram-negative (Aeromonadaceae, Vibrionaceae, Pseudomondaceae, Enterobacteriaceae, and Hafniaceae families). The premier parasitic agents include cestodes (tapeworm; e.g. Diphyllobothrium spp.), trematodes (fluke; e.g. Opisthorchis spp.), and nematodes (round worm; e.g. Anisakis spp.). In addition, protozoan organisms such as Cryptosporidium spp. are also considered fish-derived zoonotic pathogens. Two groups of fish-associated fungi causing basidiobolomycosis and sporotrichosis also pose a zoonotic risk for humans. The majority of the fish-derived zoonotic diseases are transmitted to humans mainly via the consumption of improperly cooked or raw fish or fish products. Therefore, the incidence of zoonotic diseases can be reduced by properly processing fish and fish products, e.g. by thermal (heat/freezing) treatment. The prevalence of zoonotic agents in fishes varies seasonally and should be regularly monitored to evaluate the prevalence of pathogens in both wild and cultured fish populations. This review focuses on the fish zoonotic agents/diseases and their control and prevention