Trophic interactions and the diet composition of sympatric finfish predators in the tropical demersal ecosystem in the Bay of Bengal.

The dietary composition, foraging strategies, and interspecific trophic interactions were identified for four major demersal carnivorous finfishes, namely, croaker Otolithes ruber, hairtail Trichiurus lepturus, threadfin bream Nemipterus japonicus, and lizardfish Saurida undosquamis, along the north-western part of Bay of Bengal from 2014 to 2016. Two species, Trichiurus lepturus and Saurida undosquamis, were identified as finfish feeders due to the high number of teleost (clupeids and engraulids) prey. One species, Nemipterus japonicus, had a significantly different diet of metapenaeids and charybdids, and was identified as a shellfish feeder. The final species, Otolithes ruber, preyed equally on crustaceans and teleosts, and was identified as a shellfish-finfish feeder. The feeding activity of all four species was lower during peak spawning periods and tended to increase with maturity. Feeding preferences varied with seasons. The trophic level ranged from 3.49 to 4.01, classifying the four species as medium-carnivores or meso-predators. Niche breadth ranged from 0.170 to 0.421, with seasonal and ontogenetic variations. Individual or subgroup specialization was observed on dominant prey, but intraspecific diet variations indicated all four species to be opportunistic predators. There was substantial prey overlap for Saurida undosquamis with Otolithes ruber and Trichiurus lepturus, which increased ontogenetically and coincided with their peak spawning. Sharing of abundant prey resources together with temporal and ontogenetic resource partitioning at intra- and interspecific levels possibly lowered dietary competition, thereby facilitating the coexistence of these demersal predators. This study provides new information on feeding interactions from a tropical demersal ecosystem that can be applied for the ecosystem-based management of trawl fisheries.

Description and development of Auerbachia ignobili n. sp. (Cnidaria: Myxosporea: Bivalvulida) from the giant trevally, Caranx ignobilis (Forsskål, 1775) from Indian waters.

The present study describes a new species of myxosporean, Auerbachia ignobili n. sp., infecting the hepatic bile ducts of Caranx ignobilis (Forsskål, 1775). Myxospores are club-shaped with a broad anterior region and a narrow, slightly curved and blunt caudal extension, measuring 17.4 ± 1.5 µm in length and 7.5 ± 7.4 µm in width. Shell valves asymmetrical, with a faint suture line, and enclosed a single, elongate-elliptical polar capsule with a ribbon-like polar filament, arranged in 5-6 coils. Developmental stages included early and late presporogonic stages, pansporoblast, and sporogonic stages with monosporic and disporic plasmodia. A. ignobili n. sp. differs from the other described species of Auerbachia in the shape and dimensions of the myxospores and polar capsules. The molecular analysis generated ∼1400 bp long SSU rDNA sequences and the present species exhibited a maximum similarity 94.04-94.91% with A. chakravartyi. Genetic distance analysis indicated the lowest interspecies divergence of 4.4% with A. chakravartyi. In phylogenetic analysis, A. ignobili n. sp. was positioned independently with a high bootstrap value (1/100) and appeared as sister to A. maamouni and A. chakravartyi. Fluorescent in situ hybridization and histology indicates that the parasite develops within the hepatic bile ducts. Histological studies did not reveal any pathological changes. Considering the morphological, morphometric, molecular, and phylogenetic differences coupled with the differences in host and geographic locations, the present myxosporean is treated as a new species and named A. ignobili n. sp.

New observations of the endangered giant freshwater whipray, Urogymnus polylepis, provide further evidence for its distribution and breeding in the north-east coast of India.

The present study reports observations of 13 giant freshwater whipray (Urogymnus polylepis) from commercial fish landings along the north-east coast of India and updates existing records based on field observations and local social media reports. The disc width of the landed specimens ranged from 120 to 223 cm and they weighed 95-300 kg. All 13 specimens observed were mature (nine females and four males) and three females were pregnant, with embryo numbers ranging between 4 and 15. Globally, U. polylepis is listed as 'Endangered', and greater protection measures are needed in India to assist in reversing current population declines.