TIME AND TIDE WAIT FOR NO FISH - INTERTIDAL FISHES OUT OF WATER

Hypoxic conditions are rare in the open ocean, but may occur during low tides in tidepools. Intertidal fishes respond to low tides in a variety of ways, including avoiding the intertidal zone during low tides, respiring in the well-oxygenated layer at the surface of the water, or simply tolerating hypoxic water. A number of intertidal fish species have the ability to leave the water and survive terrestrially for a period of time while breathing air. This paper reviews the literature on ecomorphology of amphibious intertidal fishes, suggests ecomorphological and ecophysiological approaches to clarifying the adaptations of intertidal fishes for emergence from water, and considers differences in the types of emergence behavior and activities seen in three broadly defined behavioral types. These types include the 'skippers', fishes that actively emerge at all phases of the tidal cycle and engage in routine terrestrial activity, the 'remainers', that emerge passively under cover such as rocks or vegetation by remaining in place as the tide recedes, and the 'tidepool emergers', that typically spend low tides in tidepools but may emerge from hypoxic water. Portioning of gas exchange between the gills and the skin, the release of CO2 into air, the effect of emergence on metabolic rate, and vertical zonation in distribution of fishes in the intertidal zone are compared for fishes in each of these behavioral styles.