Polar and cold-temperate marine teleosts (such as Antarctic notothenioids, Arctic sculpins, and winter flounder) survive in icy seawater (down to $-1.9^\circ\text{C}$) due to Antifreeze Proteins (AFPs) and Antifreeze Glycoproteins (AFGPs).
Thermal Hysteresis: AFPs adsorb specifically to emerging ice crystal prism faces via non-colligative mechanisms (Kelvin effect), pinning step growth and depressing the non-equilibrium freezing point without altering the equilibrium melting point.
The temperature difference between the non-equilibrium freezing point and melting point is known as thermal hysteresis (typically $1.0-2.5^\circ\text{C}$).
Correct Option: Option 1 (Thermal hysteresis).
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2
ICAR JRF Aquatic Environmental Management 29 Jun 2024Shift 1
MCQ (Single Correct)+4−1
--- are the enzymes responsible for the conversion of PUFAs to prostaglandins.
Cyclooxygenase activity: Bis-oxygenation and cyclization of arachidonic acid to Prostaglandin $G_2$ ($PGG_2$).
Peroxidase activity: Reduction of $PGG_2$ to Prostaglandin $H_2$ ($PGH_2$), which is then converted by tissue isomerases into prostaglandins ($PGE_2, PGF_{2\alpha}, PGD_2$), prostacyclins, and thromboxanes.
Correct Option: Option 1 (Cyclooxygenases).
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3
ICAR JRF Aquatic Environmental Management 29 Jun 2024Shift 1
MCQ (Single Correct)+4−1
The bleeding of fish contributes to one of the following phenomena in fish.
Hemeproteins as Pro-oxidants: Fish blood contains high concentrations of hemoglobin and myoglobin, which possess iron-containing heme prosthetic groups ($Fe^{2+}/Fe^{3+}$). Free heme and iron are among the most potent catalysts of lipid peroxidation in unsaturated fatty acids.
Benefits of Bleeding (Exsanguination): Immediate bleeding of fish on board (by severing gill arches or caudal peduncle) expels blood from the muscle vascular bed, substantially reducing hemeprotein-induced lipid oxidation, delaying rancidity, and preventing dark, bruised muscle discolorations.
Correct Option: Option 1 (Reduces oxidation due to the removal of hemeprotein).
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4
ICAR JRF Aquatic Environmental Management 29 Jun 2024Shift 1
MCQ (Single Correct)+4−1
Histamine intoxication results from the consumption of spoiled fish belonging to the group of
Scombroid Fishes: Scombroid fish species (family Scombridae), including tuna (Thunnus spp.), mackerel (Scomberomorus spp., Rastrelliger spp.), skipjack, and bonito, contain exceptionally high levels of free L-histidine in their dark muscle.
Histamine Formation: Inadequate post-harvest temperature control permits proliferation of bacterial contaminants possessing the enzyme L-histidine decarboxylase (e.g., Morganella morganii, Klebsiella pneumoniae, Enterobacter aerogenes), which decarboxylates histidine to toxic histamine:
Eutrophication and Volatile Suspended Solids (VSS):
Cultural eutrophication causes hyper-accumulation of limiting nutrients (dissolved nitrogen and phosphorus), triggering explosive algal blooms.
Volatile Suspended Solids (VSS): In environmental water testing, VSS represents the organic fraction of total suspended solids that volatilizes/combusts at $550^\circ ext{C}$ (composed of living and decaying algal phytoplankton cells, bacteria, and organic detritus).
Massive proliferations of phytoplankton biomass directly cause an increase in volatile suspended solids (VSS).
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