Blood flow distribution and tissue allometry in channel catfish

Blood flow (as percentage of cardiac output) in fasted channel catfish accl imated to 21 degrees C was directed primarily to white muscle (72%) followe d by head kidney (5.7%), red muscle (5.5%), trunk kidney (3.1%), liver (2.2 %), swim bladder (1.4%) and skin (1.1%). The stomach, intestines, pyloric c aeca, gonads, brain, abdominal Fat and spleen contained <0.5% of blood flow . There was considerable interfish variation among blood how distribution t o visceral organs with substantial spatial heterogeneity of blood flow to w hite muscle. The spatial heterogeneity of flow to muscle prevented accurate estimation of total flow to this tissue based on the microsphere depositio n of a few sub-samples. Instead, a novel approach, based on the whole anima l counting of the eviscerated carcass was used to measure blood flow to whi te muscle. The scaling relationships for tissue mass in catfish (63-1873 g) followed the allometric equation (aW(b)) and tended to exhibit negative al lometry, with organ weight decreasing in proportion to body weight. The b v alues for most tissues ranged between 0.83 and 1.0. The relative mass of th e brain showed the greatest decline and with a b value of 0.32. The results , together with previous data on cardiac output, permitted calculation of o rgan blood flow rates in channel catfish. (C) 1999 The Fisheries Society of the British Isles.