The ontogeny of respiration in herring and plaice larvae

Abstract

The study of larvae, their behaviour & physiology has gathered momentum in recent years due to the development of improved techniques of rearing during the past decade. Many marine larvae have been successfully reared in the laboratory (Shelbourne, 1964; Schumann, 1967; Blaxter, 1968,1969; Houde & Palko, 1970; Futch & Detwyler, 1970; Lasker, Feder, Theilacker & May, 1970). Fish larvae, in particular those of most marine species form an important tool for research in that at hatching they only possess the rudiments of most organs. Thus they are ideal material for ontogenetical studies. Although the respiratory mechanisms of adult fish have been the subject of a great deal of investigation from the point of view of gas exchange (see Randall 1970) gill structure (Hughes, 1966; Hughes & Grimstone, 1965; Newstead, 1967; to name a few) and dimensions (see Muir, 1969) gill ventilation and perfusion (see Shelton, 1970) circulatory systems (see Randall, 1970) bioenergetics, (see Brett, 1970) the respiratory systems of larvae have not been investigated in any great detail. Apart from a few studies on oxygen uptake (see Blaxter, 1969) and Harder (1954) on the development of branchial elements, no detailed study of the development of respiratory mechanisms have been made in marine fish larvae. The purpose of this study was to investigate the development of respiration in two species of marine larvae viz. the herring (Clupea harengus L.) and the plaice (Pleuronectes plates sa L.) These two species are well separated taxonomically and both adults and young have very different life histories. Herring lay demersal eggs, the plaice pelagic ones. The yolk-sac larvae of both species are planktonic, later feeding on diatoms and copepod nauplii and much later copepods. Adult herring are pelagic, living in mid water as juveniles and moving into deeper water with age, ranging from offshore to about 200m. They perform migrations partly caused by the distribution and density of food organisms. In contrast to this plaice at metamorphosis show an interesting asymmetry in that one eye migrates over the head and comes to lie against its opposite number. At this stage pelagic life ceases and the young fish assumes a bottom-living existence. Other features associated with asymmetry are secondary to the migration of the eye and follow on from the adoption of the benthic mode of life. They range from the shoreline when young to lOOOm feeding on bottom living organisms. During development the mechanism of respiration changes from a cutaneous one to gill respiration typical of the adult form. There is apparently no respiratory pigment in the early stages but the blood becomes pink at metamorphosis. The problem was approached from a morphological and a physiological viewpoint. The main parts of the study are as follows. (1) The survival times in water of low oxygen concentrations. (2) The oxygen uptake at normal oxygen concentrations. (3) The oxygen uptake at low oxygen concentrations. (4) Measurement of the body surface area as well as the gill area available for respiration. (5) The appearance of haemoglobin and its quantitative measurement.