First report of Dactylogyrus formosus from India: a case of co-existence with Paradactylogyrus catlaius causing mass mortality in Indian major carp, Catla catla.

The family Dactylogyridae, known for its role as a frequent pathogen in Cyprinids, was identified in a case of mass mortality involving Catla catla fingerlings (measuring 6.5 ± 2.0 cm and weighing 40.5 ± 10 g) in West Bengal, India. Microscopic examination revealed the presence of two co-existing parasites, Dactylogyrus formosus and Paradactylogyrus catlaius, attached to different sections of the gill filament. Despite their coexistence, these parasites exhibited marked differences in their haptoral hard parts, genital organs, and preferred habitats. Molecular analysis of the Internal Transcribed Spacer 1 and 4 genes indicated more than 90% similarity between the detected parasite and D. formosus previously reported in China. Histopathological observations illustrated the parasites' specific attachment to the distal end of the primary gill lamellae, gradually causing destruction to a maximum number of secondary lamellae. Internally, infiltration of eosinophilic granular cells was observed in gill and kidney blood vessels, while the liver exhibited hepatocytes filled with hemosiderin. The infected fish were treated for 24 h with a safe dose of common salt (5.6 ppt) and albendazole (62 ppm). The survivability rate was significantly higher (p < 0.05) in both treated groups compared to the control. Interestingly, the group treated with common salt showed superior results compared to the albendazole-treated fish. This study presents the sympatric speciation of D. formosus in a new host (C. catla) and explores its host specificity, histopathology, and treatment methods. This case marks the first report of D. formosus causing substantial mortality in cultured Catla in India, alongside the coexistence with Paradactylogyrus catlaius.

Multivariate characterization of biochemical and physiological attributes umpires Pangasianodon hypophthalmus for a welfare-based open-water cage culture.

The striped catfish, Pangasianodon hypophthalmus, dominates in the Indian inland freshwater cage culture because of its rapid growth and adaptive feeding habits; however, suitable stocking density based on growth without compromising the health of fish is important. Furthermore, fish growth and survival are inversely proportional to stocking density. Many farmers face size differentiation and poor survival at higher stocking densities. To address the aforementioned practical issue, the current study was carried out to study the influence of different stocking densities on the growth performance of P. hypophthalmus in cages. The fingerlings of P. hypophthalmus (10.63 ± 0.27 g) were stocked in triplicate in five different stocking densities (20, 30, 40, 50, and 60 m-3), and the fishes were given commercial feed for 240 days. The outcome demonstrated that the fish stocking densities and their growth attributes were inversely related. Stocking density in the range of 20 to 40 m-3 produced the highest final weight, relative growth rate, and specific growth rate. The feed conversion ratio was significantly lower in 20, 30, and 40 m-3 than the higher densities of 50 and 60 m-3. The level of serum biochemical markers such as serum glutamate oxaloacetate transaminase (SGOT) and serum glutamate pyruvate transaminase (SGPT) and glucose and cortisol levels elevated significantly in higher stocking densities. The muscle quality changed as crude fat and muscle pH decreased at 50 and 60 m-3, leading to a drop in drip loss and frozen leakage rate. The vital water quality parameters were found within a suitable range. According to the outcomes of principal component analysis (PCA), elevated levels of SGOT, SGPT, glucose, and cortisol were detrimental to fish growth. The stocking density of 30 m-3 had the highest benefit-cost ratio (B:C) and return on investment (RI), followed by 20 and 40 m-3. Higher economic return was achieved at lower densities (30-40 m-3). This study suggests that rearing P. hypophthalmus at stocking densities of about 30-40 m-3 could be considered as an optimum for the inland freshwater cage culture which gives the best performance in terms of growth and production in tropical reservoirs of India. The best-suited stocking density is also taken into consideration based on the characterization of multivariate biochemical and physiological attributes.

Ontogeny of skeletal ossification in Labeo calbasu (Hamilton, 1822) using differential fluorescence staining technique.

The present study was carried out to study the larval skeletal development in Labeo calbasu by using a modified double skeletal staining technique with Alizarin red and Alcian blue. The larval samples were obtained after induced breeding of wild L. calbasu germplasm from the River Ganga. Samples from 2 to 20 dph (day post hatching) were preserved in 4% neutral phosphate buffered formalin solution. Alizarin red and Alcian blue were used to stain the bony and cartilage parts of the skeleton, respectively. The size of the specimens ranged from 6.6 ± 0.16 to 15.6 ± 1.15 mm. The development of skeleton was observed at very early stages. A straight notochord throughout its length and origin of caudal fin rays were seen on 2 dph. The ventral spines, unbranched caudal fin rays and hypurals at ventral side of notochord were clearly visible from 4 dph. Most of the head skeletal elements and vertebral column with vertebral centrum and neural spines started appearing at 4 dph. The dorsal and caudal fins with branched rays and the opercular and jaw bones started ossifying between 10 and 20 dph. The present study gives an idea about the skeletal development process as well as detects the skeletal abnormalities in Indian major carp, L. calbasu.

Structural bioinformatics insights into the CARD-CARD interaction mediated by the mitochondrial antiviral-signaling protein of black carp.

The innate immune system offers the first line of defense against invading microbial pathogens through the recognition of conserved pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs). The host innate immune system through PRRs, the sensors for PAMPs, induces the production of cytokines. Among different families of PRRs, the retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), and its mitochondrial adaptor ie, the mitochondrial antiviral-signaling (MAVS) protein, are crucial for RLR-triggered interferon (IFN) antiviral immunity. Recent studies have shown that the N-terminal caspase recruitment domain (CARD) and transmembrane domain play a pivotal role in oligomerization of black carp MAVS (BcMAVS), crucial for the host innate immune response against viral invasion. In this study, we have used molecular modeling, docking, and molecular dynamics (MD) simulation approaches to shed molecular insights into the oligomerization mechanism of BcMAVSCARD . MD simulation and interaction analysis portrayed that the type-I surface patches of BcMAVS CARD  make the major contribution to the interaction. Moreover, the evidence from surface patches and critical residues involved in the said interaction is found to be similar to that of the human counterpart and requires further investigation for legitimacy. Altogether, our study provided crucial information on oligomerization of BcMAVS CARDs and might be helpful for clarifying the innate immune response against pathogens and downstream signaling in fishes.