Aspects of ventilation and ventilatory control were investigated in an air-breathing fish, Amia calva, to determine the extent to which Amia is similar to water-breathing fish. The possibility that Amia uses the air-breathing organ to maintain gas-exchange during periods of aestivation was tested. During gradual air-exposure, Amia showed no reduction in oxygen consumption, no increase in plasma urea levels or in urea excretion. Arterial blood pH (pHa) remained constant, and arterial plasma total carbon dioxide (TaCO₂) and carbon dioxide partial pressure (PaCO₂) increased. Arterial plasma total ammonia (Tamm) and NH₃ concentrations rose significantly. Exposure to elevated total ammonia concentrations in the water did not elicit an increase in urea production or air-breathing. Aquatic hypoxia without access to air did not cause a reduction in aerobic metabolism and moderate levels were fatal. These results indicate that Amia are incapable of aestivation, due to an inability to reduce metabolism and detoxify ammonia to urea, and die following three to five days of air-exposure. The air-breathing organ is used to maintain aerobic metabolism under aquatic conditions of hypoxia or raised temperature. The characteristics of air-breathing and gill ventilatory responses to internal acid-base disturbances were investigated in Amia. Acid infusions lowered pHa and arterial blood oxygen content (CaO₂), raised PaCO₂, and stimulated air-breathing and gill ventilation. Ammonium bicarbonate infusions did not change pHa or CaO₂, raised PaCO₂, and did not stimulate any ventilatory responses. Acid infusions during aquatic hyperoxia lowered pHa and raised PaCO₂. Arterial blood O₂ content declined but remained above normoxic levels. There were no ventilatory responses. These results indicate that air-breathing and gill ventilation responses in Amia are most closely correlated with blood O₂ status, not pHa or PaCO₂. Air-breathing and gill ventilation responses following acid infusion were associated with a release of catecholamines into circulation. Catecholamine infusion stimulated gill ventilation but not air-breathing in Amia, suggesting that endogenous catecholamine release may have mediated gill ventilatory responses to hypoxaemia. These ventilatory reflex responses to acid-base disturbance, and the correlation between gill ventilation responses and catecholamine release are similar to observations made on water-breathing fish. Ventilatory responses to increases in TaCO₂ and Tamm were investigated in rainbow trout, and compared with responses by Amia. In trout, infusion of NaHCO₃ raised pHa and TaCO₂, did not change PaCO₂ or CaO₂, and stimulated ventilation. Infusion of NH₄HCO₃ did not change pHa or CaO₂, raised TaCO₂, PaCO₂ and Tamm, and stimulated ventilation. Infusion of NH₄Cl lowered pHa, raised Tamm, and stimulated ventilation. Infusion of HCl lowered pHa, TaCO₂ and CaO₂, and stimulated ventilation. Infusion of NaOH raised pHa but did not stimulate ventilation until twenty minutes post-infusion. Infusion of NaCl had little or no effect on pHa, CaO₂, TaCO₂ or Tamm, and no effect on ventilation. These results indicate that trout show a ventilatory response to increases in TaCO₂, increases in Tamm and decreases in pHa and CaO₂, but not to increases in pHa. Following HCl and NaHCO₃ infusion, there was a significant increase in the level of circulating catecholamines, indicating that the ventilatory responses to reductions in pHa and CaO₂ and increases in TaCO₂ may be Immorally mediated by catecholamine release. The ventilatory responses to increases in Tamm were not associated with a catecholamine release. Unlike trout, Amia do not show a ventilatory response to infusion of NH₄HCO₃, i.e. to increases in TaCO₂ and Tamm. Sites and afferent pathways for ventilatory reflex responses to blood and water O₂ status were determined in Amia. Air-breathing and gill ventilatory reflex responses to hypoxia, sodium cyanide (NaCN), hypoxaemia and catecholamines were investigated in intact Amia, and compared with responses in animals following section of branchial branches of cranial nerves IX and X, and extirpation of the pseudobranch. In intact, sham-operated animals, hypoxia stimulated an increase in air-breathing and gill ventilation. Following denervation, the air-breathing response was abolished, and the gill ventilation response significantly attenuated. In sham-operated animals, NaCN in the water flowing over the gills stimulated air-breathing and gill ventilation, and NaCN given in the dorsal aorta stimulated gill ventilation. These responses were abolished following denervation. In intact animals, HC1 infusion stimulated air-breathing and gill ventilation, but following denervation, the air-breathing response was abolished. The ventilatory response to catecholamines was significantly attenuated in denervated animals as compared with shams. These results indicate that air-breathing and gill ventilation reflex responses are controlled by oxygen-sensitive receptors in the gills and pseudobranch, innervated by cranial nerves VII, IX and X. These sites and afferent pathways are similar to receptors controlling hypoxic reflex responses in water-breathing fish. The effects of catecholamines on gill ventilation are mainly exerted via stimulation of receptors in the gills, which are separate from those controlling air-breathing. The gill ventilatory responses to hypoxia, hypoxaemia and acidosis following denervation may be mediated by central effects of circulating catecholamines, or by an extrabranchial oxygen or pH receptor. In conclusion, Amia is an entirely aquatic animal with the primary ventilatory control mechanisms of water-breathing fish intact, but with the added ability to breathe air at the surface. / Science, Faculty of / Zoology, Department of / Graduate

Aspects of the resting respiration rate, specific dynamic action (SDA) and components of the total energy budget of 55 - 80g common carp were studied in the laboratory. The resting respiratory rate was monitored in computer operated metabolic chambers under different photoperiods. Common carp showed a crepuscular respiratory rhythm with peaks at dawn and dusk during a 12L : 12D photoperiod, with a mean oxygen consumption of 152 mg/kg/h. When acclimated to longer or shorter photoperiods respiration was also cyclic but with a lower mean respiratory rate. In continuous light or darkness respiratory rhythm was suppressed with no significant peakings. In carp fed with three diets containing 20,35 and 50% protein at a ration level of 0.40 to 1.00% body weight per day, SDA coefficient varied from 8.99 to 15.94% and was dependent on dietary protein but not on ration levels. SDA magnitude and post-feeding peak oxygen consumption varied significantly with both dietary protein content and total daily ration level. SDA duration was only related to ration size. The pattern of food energy allocation between the major components of the energy budget varied with dietary protein content and ration levels. The energy lost as heat of metabolism was found to increase with dietary protein level and total ration. Energy lost as faeces 'F' varied from 19 - 24% of 'C' and did not appear to be related to either protein content or ration levels. Nitrogenous excretion increased with an increase of dietary protein but decreased with an increase of ration level in the diet. Regression equations were developed from the data to allow prediction of respiratory energy loss 'R', faecal energy loss 'F' and energy lost through excretion 'U' from the food ingested V. Complete energy budget models compiled from experiments conducted over a 17 days period and using different diets did not successfully predict the actual growth. The energy budget balance was between 66.04% and 81.96%. Observed growth was less than predicted growth in every trial and it is suggested that this difference might have been due to short-term cyclic growth regulation and other minor experimental features. The data presented form the basis for the first reported study of total energy budgets in Cyprinus carpio.

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.