The present study was envisaged to generate prime information on the life history, biological characteristics, and stock status of the critically endangered smoothback guitarfish (Rhinobatos lionotus) that forms a fishery along the northwestern Bay of Bengal using length-based methods. The stock was predominantly represented by the females (Male: Female = 1:1.71). The species exhibited sexual dimorphism, where females grew bigger (Lmax = 79.0 cm) and matured at a larger size (LM50 = 43.71 cm) than males (Lmax = 61.0 cm, LM50 = 34.93 cm). Growth was allometric, where females were heavier compared to males. The life history characteristics, i.e., L∞, K, t0, M, and LC50 were 84.31 cm, 0.43 y−1, − 0.45 yr, 0.88 y−1, and 35.31 cm, respectively. The LBB analysis showed that the current biomass (B/B0 = 0.39) exceeded the level needed for maximum sustainable yield (BMSY/B0 = 0.35). The Lmean and LC50 were lower than the Lopt and LCopt, indicating growth overfishing. A sensitivity analysis revealed that the outputs of the Thompson and Bell model are highly influenced by uncertainties associated with L∞, followed by LC50, M, and K. The Thompson and Bell model revealed that the Fcurrent has depleted the SSB to a 35% level and therefore should be reduced by 18–19% to circumvent growth-overfishing (F0.1) and recruitment-overfishing (F0.4), respectively. Considering the multi-species nature of the fisheries in the region, focusing on spatial and temporal closures and strict implementation of by-catch reduction devices in the trawls are advised for the conservation and sustainable management of the species.

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Morphological changes during metamorphosis from larvae to juvenile stage vary considerably among teleosts. Metamorphosis in Acanthopagrus berda, a commercially important sparid, recorded using simple microscopy in captivity, revealed progressive changes in pigmentation, band formation, development of fins, and other morphological features. Larvae on 2 day post hatch [dph] (2—3 mm total length [TL]) exhibited an open mouth and pigmented eyes, and on 12 dph (6—7 mm TL), notochord flexion initiated with marked development in dorsal, anal and caudal fin formation. Larvae on 8 dph (3—4 mm TL) exhibited an initial internal pigmentation in the buccal cavity and 10 dph larvae were observed with an initial external pigmentation on the cephalic region. On 22 dph (11—12 mm TL), vertical band formation was initiated at the anterior portion of the larval body and proceeded posteriorly. The sequence of fin formation was in the order of pectoral, caudal, dorsal and anal fins, followed by the pelvic fin. On 45 dph (25—28 mm TL) miniature adult with fully formed silvery scales and lateral line emerged in captivity. TL bared a positive correlation with the larvae's vertical mouth opening and eye diameter. The coefficient of variation in body weight of the fish has reduced from 38 to 25% from larvae to juvenile. Information on the metamorphosis of the larvae of the species will help to act as an identification key for planktonic larvae collected from the natural environment.

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Vertebral deformities are a big challenge in Rainbow Trout seawater aquaculture. However, supportive scientific literature is missing. The present study used radiology to follow the development of vertebral deformities in a population of farmed Rainbow Trout as they grew from 36 g to 5.5 kg. In addition, separately collected deformity screening data from three other farmed populations were included for comparison. The fish developed deformities in different vertebral regions over time, eventuating to affect almost the entire vertebral column. At this point, the fish were ∼ 5.5 kg and 93 % of the fish had one or more deformed vertebrae. A negative relationship between severity of deformity (number of deformed vertebrae per individual), and fish length and weight strongly suggest a negative impact on fish welfare. The most frequently affected area was the ural region of the vertebral column. This region is a part of the caudal fin complex which also suffered from degradation of the fin rays. Ural region deformities were also frequent in the separately investigated populations. The current results indicate that Rainbow Trout are not able to maintain normal bone development under current farming conditions, consequently, jeopardizing the welfare of the fish.

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The present study documented a bloom of the comb jelly Beroe ovata occurring off Devaneri Kuppam in Mahabalipuram, close to Chennai. The abundance of the B. ovata bloom was estimated as 342 ± 21 individuals per cubic metre. A negligible number of hydromedusae specimens mixed with the comb jelly were also observed. The abundance of its predatory fish, the black pomfret (Parastromateus niger), the hydrozoan jellyfish (Aequorea pensilis), and the scyphozoan jellyfish (Cyanea nozakii) would be positively correlated with the sudden disappearance of the bloom of B. ovata on 10 October 2024. Following the bloom of B. ovata, the abundance of A. pensilis and C. nozakii led to a depletion of copepods, the main predators of dinoflagellates and diatoms, favouring the bloom of Noctiluca scintillans.

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India’s deep-sea fisheries are expanding rapidly, yet understanding of species diversity, resource availability, and conservation needs remains limited. This study examines the diversity and seasonal-temporal variation of deep-sea finfishes in the Quilon Terrace region (200–500 m depth) based on bycatch data from deep-sea shrimp trawlers collected between 2020 and 2022. A total of 144 finfish species were identified, spanning 3 classes, 31 orders, 76 families, and 108 genera. The most abundant orders were Perciformes (17.52%), Acropomatiformes (16.93%), and Scombriformes (15.58%). Biogeographically, 2 species had circumtropical and 8 circumglobal distributions, while 18 were restricted to the Indian Ocean and 22 to the Western Indian Ocean. The blackmouth splitfin (Synagrops japonicus) dominated catches in all three years (up to 19.47%), while myctophid Diaphus watasei became dominant in 2022 (26.99%). A notable presence of apex predators occupying trophic levels 4.0–4.5 was recorded. Marked seasonal differences were observed in diversity and species composition between pre- and post-monsoon periods, with limited interannual variation. Trophic structure and variability were also analyzed. Conservation analysis showed 21.5% of species were IUCN Data Deficient, and 4.6% fell under threatened categories, including Near Threatened, Vulnerable, Endangered, and Critically Endangered. The observed rise in mesopelagic species diversity in landings suggests increasing commercial interest in these resources, emphasizing the need for sustainable management and targeted conservation strategies.

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