Evaluation of water quality and bioaccumulation of metals in commercially important fishes: a human health concern.

The present study aimed to determine the physicochemical properties of the coastal water and metal concentration in the muscle tissues of five commercially important fish species (Leiognathus equulus, Lates calcarifer, Sillago sihama, Scolopsis bimaculatus, Lutjanus fulviflamma) along Thondi coast, as well as the potential human health risks on consumption of these species were also studied. Water quality parameters, such as mean temperature (31.3 ± 1.86 °C), salinity (28.35 ± 0.79‰), pH (7.95 ± 0.22), TDS (12840 ± 1.49 mg L-1), TSS (310 ± 0.51 mg L-1) and DO (5.99 ± 0.14 mg L-1) were obtained. Various nutrients such as calcium (300.0 ± 36.05 mg L-1), inorganic phosphate (0.186 ± 0.02 µg L-1), magnesium (1077.6 ± 107.01 mg L-1), nitrate (1.584 ± 0.31 µg L-1), nitrite (1.179 ± 0.34 µg L-1), silicate (29.717 ± 1.93 µg L-1) and total phosphorus (0.153 ± 0.08 µg L-1) were also analysed. The concentration of metals As, Cd, Cr, Cu, Pb and Zn in the muscle tissue was determined using atomic absorption spectroscopy (AAS). Arsenic, Cu and Pb were found to be highest in S. sihama; 1.2364 ± 0.12, 1.6102 ± 0.28 and 1.0103 ± 0.21 µg/g respectively. Cadmium and Zn were found maximum in S. bimaculatus; 0.0876 ± 0.04 and 1.0564 ± 0.16 µg/g respectively, whereas Cr was found highest in L. Calcarifer; 1.6781 ± 0.18 µg/g. Compared our results with FAO/WHO/EU regulations. The estimated daily intake (EDI) specifies that there is no risk of consuming these species. However, the target hazard quotient (THQ) in As is found to be > 1 in these fish species, which implies a possible danger to consumers.

Bioaccumulation level of metals and health risk assessment of selected red and green seaweeds validated by ICP-MS.

The bioaccumulation of trace metals in 10 selected edible seaweeds was studied using inductively coupled plasma mass spectroscopy (ICP-MS). Bioaccumulation of higher levels of manganese (4.94 ± 0.15 µg/g) and aluminium (4.21 ± 0.18 µg/g) and lower levels of arsenic (0.18 ± 0.02 µg/g) and vanadium (0.09 ± 0.02 µg/g) were observed in Chlorophyta. In Rhodophyta, bioaccumulation of iron (8.51 ± 0.19 µg/g) was high, while lower levels of magnesium (0.13 ± 0.02 µg/g) and strontium (0.21 ± 0.01 µg/g) were observed among the seaweeds studied. Health assessment studies were also conducted on seaweeds to understand their effects on human consumption. The findings imply that consuming macroalgae has no health risk due to these elements in the general population. Furthermore, the confirmative toxicity of specific metals, such as Cd, Pb, and Zn metals in macroalgae, should be monitored constantly.

Thermal stress induced hyperglycemia in the blue swimmer crab, Portunus pelagicus.

Hyperglycemia is a stress responsible mechanism induced in crustaceans through the secretion of Crustacean Hyperglycemic Hormone (CHH). The effect of thermal shock on the hemolymph CHH levels was studied in P. pelagicus. Crabs were exposed to varying temperatures for 3 h and were then transferred to ambient temperature (28 °C). A higher CHH level of 47.30 ± 2.26 fmol/ml was observed on exposure of crabs to 24 °C, over a recovery period of 3 h. This was reflected with increase in hemolymph glucose causing hyperglycemia and subsequent decrease in hepatopancreas glycogen levels. The results suggest the modulatory role of CHH in producing the energy required for the physiological reparation faced by the crabs during thermal stress.

Seasonal variation of heavy metals in seagrasses along Thondi coast, Palk Bay, India.

The present study deals with the bioaccumulation of heavy metals in different seagrass species (Syringodium isoetifolium, Halodule pinifolia, Cymodocea serrulata, Halophila ovalis) along Thondi coast and decaying seagrass offshore. Heavy metal concentrations in the seagrass samples were analysed during the period of April 2019 to March 2020 using atomic absorption spectrophotometry. Among the heavy metals assayed, the level of manganese was higher (15.62 ± 1.02 mg/kg) and chromium was the least metal observed (0.002 mg/kg). One-way ANOVA revealed significantly higher level of heavy metals in summer season, while it gradually decreased through pre-monsoon to monsoon season (P < 0.05). Cadmium and chromium were observed to be below detectable levels in the seagrass species. S. isoetifolium was found to bioaccumulate higher levels of heavy metals than the other seagrass species studied. Elucidation of heavy metal levels in the dead and decayed seagrass offshore revealed a higher level of heavy metals than live seagrass species.

Activation of prophenoloxidase and hyperglycemia as indicators of microbial stress in the blue swimmer crab Portunus pelagicus.

Portunus pelagicus is exposed to different kinds of microorganisms leading to high metabolic stress that affects its life. The present study evaluates the activity of Phenoloxidase (PO), which is an enzyme that is actively involved in the activation of the immune defense system and hyperglycemia in P. pelagicus challenged with Escherichia coli and Vibrio harveyi injections. The results revealed a major impact of microbial injection on PO activity and significant variations in hemolymph glucose and CHH levels. Reduction of glucose level was observed after 24 h microbial incubation (275.26 ± 28.85 and 175.23 ± 21.70 µg/ml in V. harveyi and E. coli injected crabs, respectively). An elevated level of CHH (13.54 ± 0.55 fmol/ml) was observed in V. harveyi-injected crabs, and increased PO activity was recorded in E. coli-injected crabs. The results of the present study indicate that microbial stress leads to the activation of the defense system and hyperglycemia in P. pelagicus.

Extraction, Characterization, and Antimicrobial Activity of Chitosan from Horse Mussel Modiolus modiolus.

Chitin and chitosan have been proved to have enormous applications in biomedical, pharmaceutical, and industrial fields. The horse mussel, Modiolus modiolus, a refuse of the fishery industries at Thondi, is a reserve of rich chitin. The aim of this work is to extract chitosan from the horse mussel and its further characterization using Fourier transform infrared spectroscopy (FTIR), micro-Raman spectroscopy, X-ray diffraction (XRD), and elemental analysis. The result of FTIR studies revealed different functional groups of organic compounds such as out-of-plane bending (564 cm-1), C-O-C stretching (711 cm-1), and CH2 stretching (1174 cm-1) in chitosan. The degree of acetylation of the extracted chitosan was observed to be 57.43%, which makes it suitable as a biopolymer for biomedical applications. Prominent peaks observed with micro-Raman studies were at 484 cm-1 (14,264 counts/s), 2138 cm-1 (45,061 counts/s), and 2447 cm-1 (45,636 counts/s). XRD studies showed the crystalline nature of the polymer, and the maximum peak was observed at 20.04°. Elemental analysis showed a considerable decrease in the percentage of nitrogen and carbon upon the conversion of chitin to chitosan, while chitosan had a higher percentage of hydrogen and sulfur. The antibacterial activities of chitosan from the horse mussel were found to be efficient at a 200 µg/mL concentration against all the bacterial strains tested with a comparatively higher antibacterial activity against Escherichia coli (9 mm) and Bacillus subtilis (8 mm).

Isolation, identification and characterization of the bioluminescent bacteria isolated from the blue swimmer crab Portunus pelagicus along Thondi Coast and virulence studies at high temperatures.

The current study was conducted to isolate the marine bioluminescent bacteria from the blue swimmer crab Portunus pelagicus along the Thondi Coast. Morphological, biochemical and molecular characterization techniques including 16S rRNA gene sequencing and phylogenetic analyses confirmed that the isolated strain was Vibrio harveyi. Experiments were further carried out at different temperatures and various time intervals and the results revealed a significant effects of high temperature and extended time duration on elimination of V. harveyi. Hence, high temperature treatments could facilitate the suppression of V. harveyi from sea food and thereby, preventing food borne infections during human consumption.

Localization and identification of crustacean hyperglycemic hormone producing neurosecretory cells in the eyestalk of blue swimmer crab, Portunus pelagicus.

This study intensely focuses on to the localization and identification of crustacean hyperglycemic hormone (CHH) producing neurosecretory cells in the eyestalk of the blue swimmer crab Portunus pelagicus. Anti-Carcinus maenas-CHH was used to identify the location of CHH neurosecretory cells by immunohistochemistry. Ten pairs of eyestalks were collected from intact adult intermoult female crab and fixed in Bouin's fixative. Eyestalks were serially sectioned and stained with chrome-hematoxylin-phloxine stain. Histological studies show the presence of different types of neurosecretory cells namely A (multipolar), B (tripolar), C (bipolar), D (unipolar), E (oval), and F (spherical) in the medulla interna, externa, and terminalis regions based on their size, shape, and tinctorial properties. The neurohemal organ, sinus gland (SG) was observed laterally between medulla interna and terminalis regions. Immunohistochemical studies showed the presence of distinct CHH-like immunoreactivity in the optic ganglia. Divergent group of neurosecretory cells with varying degree of immunoreactivity with Anti-Carcinus maenas-CHH (low, moderate, and intense reactivity) were identified in medulla terminalis, medulla interna, medulla externa, and sinus gland. The present study maps the various types of neurosecretory cells in the optic ganglia and also shows the presence of CHH-like immunoreactivity in various regions of optic ganglia in P. pelagicus. The presence of these unique neurosecretory cell types with larger cell diameter in medulla terminalis, a region that bears the neurosecretory cell bodies, suggest high secretory activity.

Induced thermal stress on serotonin levels in the blue swimmer crab, Portunus pelagicus.

The temperature of habitat water has a drastic influence on the behavioral, physiological and biochemical mechanisms of crustaceans. Hyperglycemia is a typical response of many aquatic animals to harmful physical and chemical environmental changes. In crustaceans increased circulating crustacean hyperglycemic hormone (CHH) and hyperglycemia are reported to occur following exposure to several environmental stress. The biogenic amine, serotonin has been found to modulate the CHH levels and oxidation of serotonin into its metabolites is catalysed by monoamine oxidase. The blue swimmer crab, Portunus pelagicus is a dominant intertidal species utilized throughout the indo-pacific region and is a particularly important species of Palk bay. It has high nutritional value and delicious taste and hence their requirements of capture and cultivation of this species are constantly increasing. This species experiences varying and increasing temperature levels as it resides in an higher intertidal zone of Thondi coast. The present study examines the effect of thermal stress on the levels of serotonin and crustacean hyperglycemic hormone in the hemolymph of P. pelagicus and analyzes the effect of the monoamine oxidase inhibitor, pargyline on serotonin and CHH level after thermal stress. The results showed increased levels of glucose, CHH and serotonin on exposure to 26 °C in control animals. Pargyline injected crabs showed highly significant increase in the levels of CHH and serotonin on every 2 °C increase or decrease in temperature. A greater CHH level of 268.86±2.87 fmol/ml and a greater serotonin level of 177.69±10.10 ng/ml was observed at 24 °C. This could be due to the effect of in maintaining the level of serotonin in the hemolymph and preventing its oxidation, which in turn induces hyperglycemia by releasing CHH into hemolymph. Thus, the study demonstrates the effect of thermal stress on the hemolymph metabolites studied and the role of pargyline in elevating the levels of serotonin and CHH on thermal stress in the blue swimmer crab, P. pelagicus.