RESPIRATORY-CARDIOVASCULAR PHYSIOLOGY AND CHLOROETHANE GILL FLUX IN THE CHANNEL CATFISH, ICTALURUS-PUNCTATUS

A fish respirometer-metabolism chamber was used to obtain in vivo resp iratory-cardiovascular and chloroethane gill flux data on transected c hannel catfish (Ictalurus punctatus). Methods used for spinal transect ion, attachment of an oral membrane (respiratory mask), placement and attachment of blood cannulas and urine catheters are described. Respir atory physiology, cardiac output and chemical extraction efficiencies for 1,1,2,2-tetrachloroethane (TCE), pentachloroethane (PCE), and hexa chloroethane (HCE) were determined on 419-990 g catfish. The overall m ean values (+/-S.D.) for ventilation volume (Q(v)), effective respirat ory volume (Q(w)), oxygen consumption (VO2), and percentage utilizatio n of oxygen (U) were 17.3 +/- 4.7 l h(-1) kg(-1), 9.8 +/- 1.7 l h(-1) kg(-1), 71.6 +/- 12.5 mg h(-1) kg(-1), and 49 +/- 10%, respectively, w hile cardiac output calculated via the Fick Method was 2.4 +/- 0.6 l h (-1) kg(-1). Additional measurements were made on ventilation rate (V- r), total plasma protein, haematocrit (Hct), and urine volume; while b oth arterial and venous blood were analysed for pH, oxygen partial pre ssure (PO2), carbon dioxide partial pressure (PCO2), total oxygen (TO2 ), total carbon dioxide (TCO2) and total ammonia (TAMM). Physiological measurements taken at 24 h were not significantly different from thos e taken at 48 h and indicated no deterioration of the in vivo preparat ion. All of these values agreed well with literature values on untrans ected channel catfish, except for Hct which was lower for cannulated a nimals used in this study. Overall, these data provide strong support for the use of transected channel catfish for in vivo collection of ph ysiological and chemical gill flux data. The mean initial chemical ext raction efficiencies for TCE, PCE and HCE were 41, 61 and 73%, respect ively. Chemical clearances (Cl-x) for these same three chemicals were 5.9, 9.3 and 10.8 l h(-1) kg(-1), respectively. The approximate 1 : 1 relationship between effective respiratory volume (Q(w)) and chemical clearance (Cl-x) indicated that branchial uptake of PCE and HCE was wa ter flow-limited. Chemical gill flux observed for channel catfish and chloroethanes was similar to that observed for rainbow trout in previo us studies and provided further support for the flow-limited model of chemical flux across fish gills.