Extracellular fluid volume, urine filtration rate and haemolymph mixing time in the abalone, Haliotis iris Martyn:: a comparison of 51Cr-EDTA and 14C-inulin as extracellular markers

Measurement of extracellular fluid volume (ECFV, haemolymph or blood volume) of abalone is important for understanding respiratory and circulatory functions and for investigation of factors affecting meat recovery in the fishery. The compounds C-14-inulin and Cr-51-ethylenediaminetetraacetic acid ( EDTA) were evaluated as markers for the determination of ECFV and primary urine formation ( filtration) in New Zealand blackfoot abalone or paua, Haliotis iris. The volume of distribution of either marker reliably estimated ECFV after correction for clearance (56.6 +/- 3.5mL 100 g(-1) soft tissue). Cr-51-EDTA was cleared from the haemolymph three to five times faster than C-14-inulin and was sequestered in the kidneys, digestive gland and mucous gland. 51Cr-EDTA was therefore unsuitable as a filtration marker. Urine filtration rate was best estimated from the appearance of inulin in the seawater (16.2 +/- 2.1mL 100 g(-1) soft tissue day(-1)). The ECFV ( inulin space) of isolated tissues ranged from 12-17mL 100 g-1 tissue in the digestive gland, foot and adductor muscle to 60-70mL 100 g-1 tissue in the kidneys, right ctenidium and epipodium. Equalisation of both markers between the efferent ctenidial vein and haemolymph lacunae of the shell adductor muscle occurred extremely slowly (t(1/2)similar to 2 h, t(0.95) similar to 8 h), confirming the poor perfusion of this anaerobic muscle.