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Difficulty: HardMorphological and Physiological Adaptations to Environments

Marine teleost fishes maintain osmotic balance in hypertonic seawater by drinking large amounts of water and actively excreting sodium and chloride ions across specialized cells in their gills.

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The statement is TRUE. Marine teleost fishes inhabit a hypertonic environment, causing continuous osmotic loss of water. To adapt, they drink seawater to replenish water and actively transport excess monovalent ions out of body fluids using specialized chloride cells in the gill epithelia.
The statement accurately captures the dual physiological and behavioral adaptations of marine teleost fishes. Living in a hypertonic environment, they face constant osmotic water loss. They compensate by drinking seawater and using specialized chloride cells in their gills to actively excrete excess monovalent salts.

Step-by-Step Solution

1
Analyze the osmotic relationship between marine teleost body fluids and seawater.
Marine teleost body fluids are hypoosmotic (lower salt concentration, ≈300 mOsm/L\approx 300\text{ mOsm/L}) relative to hypertonic seawater (≈1000 mOsm/L\approx 1000\text{ mOsm/L}).
This concentration difference creates a strong osmotic gradient causing passive water loss and passive salt gain across respiratory surfaces.
2
Evaluate the behavioral adaptation to passive water loss.
The fish drinks large volumes of seawater to absorb water through the intestinal tract.
Drinking seawater compensates for continuous fluid loss to the environment.
3
Evaluate the physiological mechanism for eliminating absorbed salt load.
Specialized chloride cells (ionocytes) in the gill epithelia actively pump excess sodium (Na+\text{Na}^+) and chloride (Cl−\text{Cl}^-) ions out into the surrounding sea against their concentration gradients.
Active excretion via gills prevents toxic salt accumulation while preserving internal fluid balance.

Key Concept

Hypoosmotic regulation and active ion excretion in marine teleost fishes
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Topics

Morphological and Physiological Adaptations to Environments

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