Sublethal Effects of Arsenic on Oxygen Consumption, Hematological and Gill Histopathological Indices in Chanos chanos

Background: The current study was performed aiming to evaluate possible changes in the effect on oxygen consumption, hematology and gill histopathological parameters in fish (Chanos chanos) upon exposure to sublethal concentration of the metalloid arsenic. Methods: Bioassay tests were conducted for determining the LC50 values of arsenic for 96 h. Oxygen consumption in control and arsenic-exposed fish was estimated using Winkler’s method. Red blood corpuscular (RBC) count was examined with a Neubauer counting chamber under a phase contrast microscope. Hemoglobin (Hb) was estimated following the acid hematin method. Histopathological studies were carried by processing and staining the gill tissues with hematoxylin and eosin in accordance with standard histological techniques. They were then subjected to examination under a scanning electron microscope. Results: Chanos chanos exposed to 1/10th of LC50 (24.61%) for a period of 30 days exhibited a maximum decline in the rate of respiration, followed by a decline in RBC and Hb above 45.59% and 51.60%, respectively. Significant toxic lesions encompassing fused gill lamellae, detached gill epithelium, hyperplasia and hypertrophy of respiratory epithelium became heavy handed on the 30th day. Conclusion: Information synthesized from our study serves to be useful in monitoring and managing (As) contamination in the aquatic environment.

First record of Mothocya arrosor Bruce, 1986 parasitizing Euleptorhamphus viridis (van Hasselt, 1823) from India

The first record of Mothocya arrosor Bruce, 1986 parasitizing ribbon halfbeak fish Euleptorhamphus viridis is here reported from the southeast coast of India. The important characters distinguishing M. arrosor from other species in the genus include the body slightly twisted to one side, dorsum weakly convex, coxae of pereonites 6 and 7 distinctly rounded, pleon more completely overlapped by pereonite 7, pleonite 1 scarcely visible in dorsal view, uropod peduncle longer than rami, lacking strongly convex medial and lateral margins. The damage of gill rakers and erosion of gill lamellae were the acute gross lesions observed as a result of isopod infestation.

Susceptibility of Goldfish to Cyprinid Herpesvirus 2 (CyHV-2) SH01 Isolated from Cultured Crucian Carp

Cyprinid herpesvirus 2 (CyHV-2), a member of the Alloherpesviridae family belonging to the genus Cyprinivirus, is a fatal contagious aquatic pathogen that affects goldfish (Carassius auratus) and crucian carp (Carassius carassius). Although crucian carp and goldfish belong to the genus Carassius, it is unclear whether they are susceptible to the same CyHV-2 isolate. In addition, the origin of the crucian carp-derived CyHV-2 virus isolate remains unclear. CyHV-2 SH01 was isolated during herpesviral hematopoietic necrosis disease (HVHN) outbreaks in crucian carp at a local fish farm near Shanghai. CyHV-2 SH01 was confirmed by PCR and Western blot analysis of kidney, spleen, muscle, and blood tissue from the diseased crucian carp. Moreover, histopathological and ultra-pathological analyses revealed pathological changes characteristic of CyHV-2 SH01 infection in the tissues of the diseased crucian carp. In the present study, goldfish and crucian carp were challenged with CyHV-2 SH01 to elucidate viral virulence. We found that CyHV-2 SH01 could cause rapid and fatal disease progression in goldfish and crucian carp 24 h post-injection at 28 °C. Experimental infection of goldfish by injection indicated that the average virus titer in the kidney of the goldfish was 103.47 to 103.59 copies/mg. In addition, tissues exhibited the most prominent histopathological changes (cellular wrinkling and shrinkage, cytoplasmic vacuolation, fusion of the gill lamellae, and hepatic congestion) in CyHV-2 SH01-infected goldfish and crucian carp. Thus, crucian carp and goldfish showed a high sensitivity, with typical symptoms, to HVHN disease caused by CyHV-2 SH01.

Infection prevalence, intensity, and tissue damage caused by the parasitic flatworm, Bdelloura candida, in the American horseshoe crab (Limulus polyphemus)

Parasite infection dynamics can have profound implications on a host’s fitness; yet, there is a dearth of information on parasites in the American horseshoe crab (Limulus polyphemus) (Linnaeus 1758), a species that has experienced population declines in recent decades. Therefore, we aimed to quantify the prevalence, intensity, and gill surface area coverage of the ectoparasitic flatworm (cocoon and adult stages), Bdelloura candida in adult (n = 29), sub-adult (n = 7) and juvenile (n = 32) horseshoe crabs collected from Moriches Bay, NY (40.7810° N, 72.7171° W) in 2019 and 2020. Subsamples of horseshoe crab gill tissue (10%) were collected from live specimen, then B. candida cocoons were enumerated across the gill subsamples using microscopy while the extent of tissue damage was quantified with histology. B. candida was present in all adult and sub-adult crabs (100%), whereas juveniles exhibited 6.2% prevalence. Cocoon intensities per sample ranged from 28 to 805 cocoons, with 4.0–94.0% of gill lamellae harboring cocoons. In infected individuals, the total cocoon surface area coverage on gill tissues ranged from 0.06–14.51%, with higher cocoon intensities observed in the ventral-most gill quartiles relative to the dorsal-most gill regions. Sex was strongly supported as a primary driver behind B. candida infection intensities with adult females harboring higher intensities. Among infected gill lamellae, cocoon intensity was lower in mitochondrial-rich regions relative to mitochondrial-poor regions. These results provide novel insight into B. candida infection dynamics across horseshoe crab demographics, but further research is necessary to quantify the physiological impacts of the infection on L. polyphemus.

Gastrodermis ultrastructure of the different life stages of the polyopisthocotylean monogenean gill parasite Discocotyle sagittata

The polyopisthocotylean Discocotyle sagittata is a blood-feeding monogenean that infects the gill lamellae of rainbow trout, Oncorhynchus mykiss, and brown trout, Salmo trutta. The ultrastructure of their alimentary tract, at different stages of the life cycle, was previously unknown. Here, we show that the gastrodermis of the oncomiracidium, subadult, and adult D. sagittata follows the same structural organization as that of other blood-feeding polyopisthocotyleans, being composed of digestive cells alternating with a connecting syncytium. Digestive cells of the oncomiracidium are found in three developmental forms: undifferentiated, developing differentiated, and differentiated (presumably functioning) cells whereas those of adult and subadult are present in a single functioning state with variable size and content. The apical cytoplasm of adult digestive cells forms conical outgrowths, a feature which is absent in the oncomiracidium. The connecting syncytium of the oncomiracidium has no evidence of metabolic activity, while that of adult and subadult is metabolically active. The lamellae of the connecting syncytium of adults and subadults are more numerous and larger, and their terminal portions are expanded, compared with those of the oncomiracidium. Parallel, tubular, membranous structures are characteristic of the apical cytoplasm of the connecting syncytium of the oncomiracidium. Luminal lamella in the oncomiracidium, subadult, and adult form balloon-like structures enclosing some luminal contents, but those of the oncomiracidium are larger, bounded by nucleated cytoplasmic layer, and enclose more luminal contents. The possible functions of these structures and mechanism of digestion in both oncomiracidium and adult are discussed.

Histopathological alterations in the gills of banded gourami (Trichogaster fasciata) exposed to thiamethoxam

Thiamethoxam (THM) is a widely used agro-pesticide in Bangladesh, though European Union has banned this neonicotinoid insecticide due to its toxic effects on non-target organisms. A 60-day experiment was conducted to study the effect of sub-lethal concentrations of THM on gills of Banded Gourami Trichogaster fasciata. The experiment was conducted in 15 PVC tanks each containing 100L water. The 96-h LC50 value of THM was estimated as 161.06mg/L for Banded Gourami. Based on estimated 96-h LC50 value, the experiment was carried out using a control (0 mg/L of THM) and five sub-lethal concentrations (9.37, 18.75, 37.5, 75 and 150 mg/L of THM in water) with three replications. For collection of gills, fishes were sampled on day-30 and day-60 of exposure to THM. Several histopathological changes were observed in the gill tissues of treated fishes viz. clubbing and reduction of gill filaments, telangiectasis of gill lamellae, haemorrhage and damage of gill raker. Water quality parameters (e.g. DO, pH and temperature) were recorded every 15 days interval. The DO levels were found to decrease significantly with increasing THM concentrations and time of exposure, whereas no noticeable changes were observed for pH and temperature. Therefore, neonicotinoid crop insecticide like THM is capable of damaging gill tissues of an small indigenous fish Banded Gourami.

Molecular epidemiology of helminth diseases of the humpback grouper, Cromileptes altivelis, as a pattern for mapping fish diseases in the Sunda Strait, Indonesia

Background and Aim: Neobenedenia girellae and Haliotrema epinepheli are important but neglected helminth parasites of marine fish. The humpback grouper, the most relevant definitive host, harbors several Neobenedenia and Haliotrema spp. simultaneously on body surfaces and gills. These species can be distinguished morphologically This study aimed to identify Neobenedenia and Haliotrema spp. infestations in monogenean humpback grouper by multiplex polymerase chain reaction method, which seems to be widely distributed in the study area. Data can be used as a basis for mapping disease patterns in Strait waters. Materials and Methods: Eighty humpback groupers (Cromileptes altivelis) were collected from eight different areas in the Sunda Strait and examined using scrapings from body surfaces and gill lamellae followed by multiplex PCR for identification. Results: Parasites on body surfaces were recovered from 49 fish (61.2%) and were found on gill lamellae in 72 fish (90%) by microscopic examination. Endoparasites were absent. Ectoparasites identified included, N. girellae, Neobenedenia melleni eggs, Neobenedenia pasifica, Neobenedenia longiprostata, Haliotrema eukurodai, H. kurodai, Haliotrema leporinus, Haliotrema dongshaense, Haliotrema angelopterum, Haliotrema aurigae, Haliotrema scyphovagina, and H. epinepheli. Conclusion: The distribution of trematode disease in humpback grouper in Sunda Strait waters was revealed. All parasites were from genera, Neobenedenia and Haliotrema. Risks associated with these parasites should not be overlooked. Prevention and control programs need to be extended to other marine fish. Humpback grouper should be dewormed more frequently.

A STUDY OF HISTOPATHOLOGICAL CHANGES IN THE GILL AND LIVER TISSUES OF FRESHWATER FISH HETEROPNEUSTES FOSSILIS EXPOSED TO CYPERMETHRIN TOXICITY

The synthetic pyrethroid, cypermethrin toxicity was studied in fresh water fish 'Heteropneustes fossilis and the tissues like gill and liver were chosen for Histopathological effects by light microscopy, for 4 days and 7 days under sublethal concentrations. No Histopathological effects were observed in control group and 4 days group. Hence 7 days group was selected for the present study. Significant changes in Hepatic cells of liver were observed like cloudy swelling of hepatocytes, vacuolour degeneration, and dilation of sinusoids, Hepatic lesions, and Karyo Lexis. In Gill, oedema, Epithelial lining, curling of lamellae were observed. This study demonstrates the potential of electron microscopy in particular SEM, as a tool for detecting cypermethrin induced damage to liver and surface of gill lamellae.

Amyloodinium sp. (Brown, 1931) (Dinoflagellida) infestation in captive stock of silver moony, Monodactylus argenteus (Linnaeus, 1758)

This study was undertaken to investigate the cause of mortality in the captive stock of silver moony Monodactylus argenteus. The fishes showed severe infection of dinoflagellate protozoan Amyloodinium sp. (Blastodinida, Oodiniaceae) on gills and skin with complete mortality of the stock within a week. Histopathological changes were evident in the gill tissues with severe lamellar epithelial cell hyperplasia and lamellar fusions with the presence of trophonts of Amyloodinium sp. Scanning electron microscopy (SEM) also revealed trophonts of Amyloodinium sp. of varying sizes in groups consisting of 3 to 5 trophonts tightly attached to gill lamellae. Source water contaminated with the tiny infectious form of the parasite (dinospores) favoured by higher salinity and low water temperature in the rearing tank could be the triggering factor for the spurt of infections. Proper quarantine and biosecurity protocols to prevent the potential sources of water-borne infection sources are likely to be far more effective than treatment.