Sensitivity of restrained skipjack tuna ( Katsuwonus pelamis) to abrupt increases in temperature

1. 1. Restrained skipjack tuna ( Katsuwonus pelamis) signaled by deceleration of heart rate that they could perceive abrupt temperature increases (1°C/sec) as small as 1°C. 2. 2. A thermal stimulus directed into the oral-branchial cavity was more effective in eliciting responses than stimuli delivered to the nasal cavity or the dorsal, anterior quadrant of the body surface. This finding is discussed in relation to the current belief that thermal sensors in fish are generously scattered over the skin surface.