Fishery, population parameters and stock estimates of the bigeye thresher Alopias superciliosus Lowe, 1841 from the Thoothukudi coast of Gulf of Mannar Marine Biosphere Reserve (GoMMBR) was studied during the period 2015 to 2019. Results of the study reveals that the estimated annual average production of sharks from Thoothukudi region was 105 t of which the dominant shark species was A. supercilious (52.70%). The length of the sampled A. supercilious ranged between 108 and 265 cm. Results of the length-weight relationship showed negative allometric growth with b value of 2.66. The growth parameters viz, asymptotic length (L?), growth co-efficient (K) and arbitrary origin of growth (t0 ) were estimated at 367 cm, 0.39 y-1 and 0.12 respectively. The mortality parameters viz, total mortality (Z), fishing mortality (F) and natural mortality (M) rates were estimated at 1.20, 0.70 and 0.50 y-1, respectively. In Thoothukudi, the recruitment season of A. superciliosus was found during March and October showing optimal exploitation with exploitation rate (E) of 0.58 and the estimated exploitation ratio (U) was 0.54. The virtual population analysis (VPA) showed a fishing pressure on the 240 to 320 cm length group. The estimated annual catch and maximum sustainable yield (MSY) were 58 and 68 t respectively. The present study gives valuable baseline information on the fishery and population characteristics of this vulnerable and data deficit resource A. superciliosus off Thoothukudi.
The present study describes the isolation, characterization and antibacterial activity of two strains of the deep purple pigmented bacterium Pseudoalteromonas luteoviolacea designated P42 (Accession no. MN647538) and M64 (Accession no. MN647537), isolated from two coral reef regions viz. Minicoy Lagoon in the Lakshadweep Sea and Palk Bay, off Olaikuda village in Tamil Nadu, India. Ultrastructural examinations were done using scanning and transmission electron microscopy. Presence of violacein pigment was qualitatively analysed by chemical methods; UV-VIS spectrophotometry and FTIR spectroscopy. The strains, P42 and M64 were found to have antibacterial activity against 13 out of the 36 marine bacterial species tested. Antibiogram analysis revealed the sensitivity of both the strains to all the antibiotics tested, except for the resistance of P42 to Penicillin G and Trimethoprim. This study reports the isolation and characterization of P. luteoviolacea for the first time from India. Since both the isolated strains have shown clear evidence for the presence of violacein as well as antibacterial activity against selected marine bacteria, both P42 and M64 can be suggested as potent antibacterial agents.
The present study was undertaken to standardise the conditions for activity optimisation of agarases produced by three distinct strains of agar degrading bacteria viz, Flammeovirga yaeyamensisAM5.A, Aliagarivorans marinusAM17.E1 and Aliagarivorans taiwanensisA69.B2 (GenBank Acc. Nos. MT473965; MT475710 and MT473967 respectively) isolated from coral reef ecosystems along the southern coast of India. Agarase from F. yaeyamensis exhibited highest activity at 40°C, while A. marinus and A. taiwanensis agarases had peak activity at 50°C. The optimal pH and incubation time for agarases from all the three strains were 7.0 and 45 min respectively. The partially purified enzyme-extracts from the three strains were further studied for their responses to the presence of various metal ions (Cu2+, K+, Hg2+, Mn+, Na+ and Ca2+); a chelating agent, ethylenediamine tetraacetic acid (EDTA); a reducing agent, mercaptoethanol and a serine protease inhibitor, phenyl methyl sulfonyl fluoride (PMSF). Enzyme characterisation results clearly indicated the sensitivity of all the three agarases to Hg2+ and Na+ ions. Cu2+ ions were found inhibitory to the enzyme from A. taiwanensis and A. marinus. However, F. yaeyamensis derived agarases remained unaffected even at 5 mM concentrations of Cu2+. Presence of K+ ions evidently suppressed the agarases from F. yaeyamensis and A. marinus. EDTA, mercaptoethanol and PMSF were found to be inhibitors of the enzyme activity, while Mn+ and Ca2+ had additive effect. The results of the study indicated potential of the bacterial strains investigated in this study as prospective sources of agarases.
Understanding the trade-offs in tropical reservoir fishery in a socio-ecological perspective
Bivalve molluscs have been regarded as excellent bioindicators of environmental pollution as they persistently accumulate toxic contaminants present in their ecosystem. Histological alterations in the digestive gland and gills of three bivalve sp., Viz. edible oyster (Magallana bilineata), green mussel (Perna viridis) and black clam (Villorita cyprinoides) from ecologically sensitive regions of international significance on the southwest coast of India were evaluated using a semi-quantitative histopathological index to assess the environmental quality. The prominent tissue alterations included tubular vacuolation, haemocytic infiltration, parasitosis, lamellar disorganization, and the presence of prokaryotic inclusions. The presence of ten trace metals was also evaluated in the digestive gland of bivalves. The histopathological indices were evaluated season-wise and region-wise. Seasonal variation in all the reaction patterns was observed in the digestive gland across sampling zones, with the highest indices observed during post-monsoon. The indices for all the reaction patterns in the digestive gland were significantly higher in bivalves from Vembanad Lake (Z4), followed by Periyar River (Z5). The indices for cellular changes and parasitosis in gills were the highest in the Ashtamudi estuary (Z1) and Z5, respectively. The global histopathological indices of the digestive gland and gills were also the highest in Z4, followed by Z5. Principal component analysis revealed that Z4 was distinct with the highest metal pollution index. A positive relation was observed with heavy metals, digestive gland histological alterations, and season and region of sampling.
The high species diversity in tropical coral ecosystem indicates that it is driven by diferent set of mechanisms which are beyond conventional allopatric ecological speciation models, because geographical barriers are limited in marine ecosystems. Specifc diferences were observed in shell coloration of Conus catus (Hwass in Histoire naturelle des vers. volume 1. Pancoucke, Paris, 1792), specimens collected from adjacent ecologically diferent habitats. Maximum likelihood clustering approaches were done based on mitochondrial genes, Cytochrome oxidase I (COI) and 16S ribosomal RNA (16S rRNA) genes. Multiple molecular marker–based analyses revealed that coral reef ecological niche–dependent adaptive divergent evolutionary selective pressure is acting on both coding and non-coding mitochondrial markers. Adjacent ecologically different habitats like rocky shore and subtidal coral reef fats in Lakshadweep Islands have less genetic connectivity compared with geographically separated similar ecosystems like rocky shores in Arabian sea, Bay of Bengal, and Pacifc Ocean. These haplotype variations are giving new insights into the evolutionary genetic process hidden in ecological speciation of molluscs. We also observed that Conus striolatus (Kiener in Icon. des Coq. Viv., 2, 1845), a morphologically similar species to rocky shore C. catus, is the outcome of sympatric speciation through the modifed niche-dependent selection pressure exerting on each other in rocky intertidal ecosystems. The present study revealed that ecotypes of C. catus are in the way of parapatric speciation and remind that basic unit of biodiversity conservation should be the habitat apart from the species.