The effects of stress on hematology and energy metabolism in marine fishes

Abstract

Stress responses to exercise were compared for two tropical teleosts. The sweetlip emperor (Lethrinus chrysostomus), a relatively active species, increased plasma catecholamines after 1 min exercise. Exhaustive exercise increased hematocrit (Hct) and hemoglobin (Hb) by 38 and35%, respectively, and plasma lactate increased from 0.42±0.05 to 4.31±0.35 mmol L-1. In contrast, the wire-netting cod (Epinephelus merra), a benthic fish, did not increase catecholamines after exhaustive exercise. Hct and Hb increased by 28 and 23%, respectively, with exhaustive exercise, and lactate increased from 0.26±0.33 to 1.91±0.89 mmol L-I. Incubation of erythrocytes with adrenaline resulted in 8.4% increase in hematocrit, due to cell swelling, this was minimal compared to the l8.7% increase observed for the sweetlip emperor. This supports the hypothesis that fish with higher levels of activity require secondary stress responses to increase oxygen transport and prevent detrimental effects of metabolic acidosis on oxygen transport, both during and after extended anaerobic exercise. Exercise nearly doubles the hematocrit of the pelagic nototheniid Pagothenia borchgrevinki. This contrasts with the lack of hematological responses shown by the less active benthic Trematomous bernacchii. Lactate levels in white muscle reached 5.7±0.6 μmol g-1 and 14.7±1.3 μmol g-1, following 10 min exercise, in T. bernacchii and P. borchgrevinki, respectively. Glycogen levels in the pectoral muscle of T. bernacchii were nearly 3 fold higher than those of. P. borchgrevinki. It is suggested that for red muscle n τ. Bernacchii, significant levels of lactate do not accumulate, and fast and slow muscle fibres within the pectoral muscle of τ. bernacchii maintain lactate levels in a steady state. Primary and secondary stress responses were measured in wild and captive blue mao mao (scorpis violaceus) subjected to burst swimming. Plasma lactate levels accurately reflected work done during exercise by wild fish, and correlated with rising catecholamine levels. Wild fish increased Hb levels and demonstrated significant erythrocyte swelling during intense exercise, but in captive fish erythrocyte MCHC remained constant, despite increased Hb. Altered activity patterns and unknown consequences of laboratory acclimation raise doubts about the physiological status of captive fish. Hematological indices and the erythrocyte nucleotides, ATP and GTP, remained unchanged following strenuous exercise in the shovelnosed ray (Rhinobatos batillum. Marked increases in plasma lactate pointed to a post-exercise metabolis acidosis which, through the Hb-Bohr effect, is expected to impair oxygen loading in the gills during aerobic recovery. Both adrenaline and noradrenaline were sharply increased after strenuous exercise with adrenaline the dominant catecholamine. These endocrine responses were not coupled to plasma lactate, and did not result in erythrocyte swelling. These responses predict that the ability of the rhinobatoid ray to resume aerobic activity following burst exercise is limited.