Respiratory Currents of Flatfish

Abstract

WE have observed specimens of the following species of flatfish (Pleuronectiformes) in an aquarium with a transparent bottom: Scophthalmus maximus (L.) (Bothidae); Limanda limanda (L.), Pleuronectes platessa L. and Platichthys flesus (L.) (Pleuronectidae); Solea solea (L.) and Buglossidium luteutn (Risso) (Soleidae). When these fish are resting on the bottom, both opercula move in the manner usual in teleost respiration. When a suspension of carmine in sea water, or ink diluted with sea water, is released from a pipette such that it is drawn into the mouth with the respiratory current, however, it is normally expelled solely through the upper opercular opening (that is, the opercular opening of the ocular side). Hughes¹ thought that a greater volume of water issued from the upper opercular opening than from the lower one of Pleuronectes resting on the bottom, but did not find much difference in volume between the two sides. We, however, did not see carmine or ink expelled from the lower opercular opening except when the fish were behaving in an agitated manner.