THORAX ABDOMEN AND PELVIS

Detailed explanation-1: -Fishes in water excrete ammonia as the major nitrogenous waste through gills, but gills of air-breathing fishes are modified for air-breathing or largely replaced by air-breathing organs. Notably, fishes emerged from water can no longer excrete ammonia effectively because of a lack of water to flush the gills.

Detailed explanation-2: -The gills are the primary site of ammonia excretion in fish (Wilkie, 1997, 2002; Weihrauch et al., 2009), because they have large surface area, perfusion by 100% of cardiac output, large ventilation rates, small diffusion distances, and contact with a voluminous mucosal medium (Evans et al., 2005).

Detailed explanation-3: -Ammonia is eliminated from the blood upon passage through the gills. The mechanisms of branchial ammonia excretion vary between different species of fish and different environments, and primarily involves NH3 passive diffusion and NH4 (+)/Na(+) exchange.

Detailed explanation-4: -Final answer: Yes, Marine fish excrete urea.