DIEL PATTERN OF HEMATOCRIT, SERUM METABOLITES, OSMOTIC-PRESSURE, ELECTROLYTES AND THYROID-HORMONES IN SEA BASS AND SEA BREAM

The diel pattern of haematocrit, serum metabolites, electrolytes and t hyroid hormones are described in sea bass, Dicentrarchus labrax, and s ea bream, Sparus auratus, held under 12L:12D light cycle (0600-1800 h light). No diel rhythmicity in haematocrit, total proteins, potassium and chloride was observed. Maximum Values of glucose, osmotic pressure and sodium were recorded at dusk (1800 h) in both species, irrespecti ve of differences in the size of fish and feeding regime used. Maximum and minimum triiodothyronine values were found during the scotophase in bass and during the photophase in bream. Maximum thyroxine levels o ccurred at 1400 h (bass) and 1800 h (bream) and minimum during the sco tophase, in both species. The light/dark alternation seems to be an im portant synchronizer of the observed diel changes. Results are discuss ed in relation to the timing of feeding and the general activity of th e fish.