Mucosal and Systemic Immune Responses to Salmon Gill Poxvirus Infection in Atlantic Salmon Are Modulated Upon Hydrocortisone Injection

Salmon Gill Poxvirus Disease (SGPVD) has emerged as a cause of acute mortality in Atlantic salmon (Salmo salar L.) presmolts in Norwegian aquaculture. The clinical phase of the disease is associated with apoptotic cell death in the gill epithelium causing acute respiratory distress, followed by proliferative changes in the regenerating gill in the period after the disease outbreak. In an experimental SGPV challenge trial published in 2020, acute disease was only seen in fish injected with hydrocortisone 24 h prior to infection. SGPV-mediated mortality in the hydrocortisone-injected group was associated with more extensive gill pathology and higher SGPV levels compared to the group infected with SGPV only. In this study based on the same trial, SGPV gene expression and the innate and adaptive antiviral immune response was monitored in gills and spleen in the presence and absence of hydrocortisone. Whereas most SGPV genes were induced from day 3 along with the interferon-regulated innate immune response in gills, the putative SGPV virulence genes of the B22R family were expressed already one day after SGPV exposure, indicating a potential role as early markers of SGPV infection. In gills of the hydrocortisone-injected fish infected with SGPV, MX expression was delayed until day 10, and then expression skyrocketed along with the viral peak, gill pathology and mortality occurring from day 14. A similar expression pattern was observed for Interferon gamma (IFNγ) and granzyme A (GzmA) in the gills, indicating a role of acute cytotoxic cell activity in SGPVD. Duplex in situ hybridization demonstrated effects of hydrocortisone on the number and localization of GzmA-containing cells, and colocalization with SGPV infected cells in the gill. SGPV was generally not detected in spleen, and gill infection did not induce any corresponding systemic immune activity in the absence of stress hormone injection. However, in fish injected with hydrocortisone, IFNγ and GzmA gene expression was induced in spleen in the days prior to acute mortality. These data indicate that suppressed mucosal immune response in the gills and the late triggered systemic immune response in the spleen following hormonal stress induction may be the key to the onset of clinical SGPVD.

Health and disease status of cultured Gulsha (Mystus Cavasius) at Mymensingh region of Bangladesh

A study was carried out for a period for four months from January to April 2019 in eight fish farms at Mymensingh region of Bangladesh. The principal objectives were to study the health status of gulsha in four months from eight farms in Mymensingh region as well as month wise pathological changes of various organs of gulsha through clinical and histopathological observations. Clinical signs of fish were reddish lesion and mild injured in different parts of body, abrasion, whitish spots etc. Gills of fish showed more pathological changes than skin, muscle and liver. Histopathologically, gills of all fish species were more affected in Nuha Aqua Farm than other seven fish farms of Mymensingh in January and February. General gill pathology of the fishes was lamellar missing, haemorrhage and hypertrophy. Pathology of skin and muscle of the fishes from different farms included epidermal missing, necrosis, vacuum and loss of muscle. Fat bodies, necrosis, vacuum and haemorrhage were the common pathology of liver in the fishes from sampled farms of Mymensingh. Mainly fat bodies, vacuum and necrosis were found in Sharnalata Agro Fisheries, Relience Aqua Farm, Nuha Aqua Farm and Manju Aqua Farm. On the contrary, haemorrhage and necrosis were noticed in Chan Mia Fish Farm, Fish Seed Multiplication Farm; Maskanda and Setu Hatchery and Aquaculture in Tarakanda. In the months of March and April different organs of gulsha fish like gill, skin, muscle and liver were recorded almost normal structure from sampled fish farms. Fish were found to be affected during colder months of January and February. But, during March and April most of the fish were found normal and healthy. From field and laboratory observations it was revealed that the study area had potentiality for gulsha culture, although necessary measures need to be taken especially during winter season. Res. Agric., Livest. Fish.7(1): 139-151, April 2020

Black sea bass are a host in the developmental cycle of Lernaeenicus radiatus (Copepoda: Pennellidae): insights into parasite morphology, gill pathology and genetics

Lernaeenicus radiatus, a mesoparasitic pennellid copepod, has long been known in the northwest Atlantic with metamorphosed females infecting the muscle of marine fish. The study herein is the first to identify a definitive first host, black sea bass Centropristis striata, for L. radiatus supporting larval development to adults and sexual reproduction in the gills. This finding suggests a two-host life cycle for L. radiatus, with black sea bass as the first host. Heavy infections in the gill were associated with considerable pathology related to a unique and invasive attachment process that penetrated the gill and selectively attached to the gill filament cartilage. The morphology of the developing copepod was highly conserved with that of a related pennellid copepod, Lernaeocera branchialis, though was distinguished by the attachment process, unique pigmentation and other morphologic features described herein. Sequencing the small and large subunits of the ribosomal RNA and mitochondrial cytochrome c oxidase subunit I genes demonstrated L. radiatus to share closer identities with Lernaeocera and Haemobaphes spp. pennellid copepods rather than other Lernaeenicus spp. available in GenBank to date. Taxonomy of L. radiatus is discussed in relation to life cycles, tissue tropism, morphology and genetics of other closely related pennellid copepods.

Cryptic hydrozoan blooms pose risks to gill health in farmed North Atlantic salmon (Salmo salar)

Sampling at four salmon aquaculture sites along the west coast of Scotland has identified short-lived aggregations of planktonic hydrozoans (>280 individuals m−3), here termed blooms. Several such blooms were linked with increases in gill pathology and mortality in caged fish. Two types, Obelia sp. and Lizzia blondina, were found to cause blooms regularly and often concurrently. Species composition of hydrozoan populations and fluctuations in population sizes were spatially and temporally heterogeneous, with adjacent sites (within 30 km of one another and with similar oceanic exposure) experiencing no correlation between species composition and population density. Blooms appeared temperature-mediated, with all identified blooms by Obelia sp. and L. blondina taking place in water above 12 °C; however, temperature alone was not found to be predictive. Blooms were not significantly associated with change in salinity, water clarity, or photoperiod. Due to the apparent lack of broadly applicable predictors, we suggest that localized, targeted sampling and examination of planktonic hydrozoan populations is required to discern the presence or absence of a bloom. It is likely that many blooms have historically caused harm in salmon aquaculture while remaining unrecognized as the root cause.

A Survey of Gill Histopathology of Thirteen Common Fish Species in the Sanyati Basin, Lake Kariba, Zimbabwe/ Badania Histopatologiczne Skrzeli Trzynastu Pospolitych Gatunków Ryb W Zlewni Sanyati, Jezioro Kariba, Zimbabwe

Following a study of gill pathology in African catfish (Clarias gariepinus) and Nile Tilapia (Oreochromis niloticus) from the Sanyati Basin of Lake Kariba, Zimbabwe, a similar survey was carried out in thirteen other common fishes of Lake Kariba. Gill tissues were dissected from the fish, preserved and prepared for histology. The prepared tissue sections were observed under a light microscope. Six histopathological lesions were observed, namely epithelial lifting, hyperplasia, lamellae fusion, parasitic cysts, oedema, and aneurysm. Epithelial lifting was prevalent in all fish species whilst aneurysm was only observed in two fish species. Synodontis zambezensis had the highest prevalence of gill lesions whilst Marcusenius microlepidotus, Brycinus imberi and Micralestes acutidens had the least prevalence of lesions. Most of these histopathological lesions were mild to moderate, and this is suggestive of good health of the fish species investigated. Seventy seven percent of the fish species were infected with monogenean ectoparasites. More research on fish health in Lake Kariba is recommended and future studies should aim to quantify these histological changes in relation to environmental conditions of the lake. This will enable histopathology to be used as a biomarker or predictor of water quality.