In commercial aquaculture ponds, the unionized ammonia-nitrogen ($\text{NH}_3\text{-N}$) fraction becomes hazardous to cultured finfish and crustaceans at concentrations approaching and exceeding $0.1\text{ mg N/L}$.
Thermal Stratification in Reservoirs: Metalimnion:
In deep reservoirs and lakes, vertical thermal stratification establishes three distinct zones:
Epilimnion: Upper warm, circulating water layer.
Thermocline (Metalimnion): A dynamic transition layer where water temperature drops drastically with depth (defined as a temperature decrease $\gt 1.0^\circ\text{C}$ per meter of depth).
Hypolimnion / Tropholytic Zone: Cold, uncirculated, dark benthic layer where decomposition exceeds photosynthesis.
Correct Option: Option 1 (Tropholytic zone - as per official key; limnologically Thermocline/Metalimnion).
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14
ICAR JRF Aquaculture 29 Jun 2024Shift 1
MCQ (Single Correct)+4−1
The water stability of shrimp feed should be minimum of.
Shrimps (Penaeus vannamei, Penaeus monodon) are slow, continuous bottom feeders that manipulate and nibble feed pellets slowly using their maxillipeds and mandibles.
To prevent rapid physical disintegration and nutrient leaching into the water, commercially formulated shrimp feeds must exhibit a minimum water stability of 2 hours (retaining $\ge 85\%$ of their physical dry mass intact).
Correct Option: Option 3 (2 hours).
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15
ICAR JRF Aquaculture 29 Jun 2024Shift 1
MCQ (Single Correct)+4−1
Which one of the following is harmful for the carp spawns?
Newly hatched carp spawn ($5-7\text{ mm}$) possess poor swimming mobility and thin cuticles, making them highly vulnerable to aquatic hemipteran and coleopteran insect predators.
Anisops spp. (Backswimmers, family Notonectidae): Voracious aquatic predatory bugs that grasp carp spawn with their raptorial forelegs and inject piercing-sucking digestive enzymes, killing hundreds of carp larvae within hours.
Brachionus, Keratella, and Ceriodaphnia are beneficial non-predatory zooplankton that serve as primary food.
Correct Option: Option 1 (Anisops).
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