Effects of graded environmental hypercapnia on sea bass (Dicentrarchuslabrax L.) feed intake and acid-base balance

摘要

The effect of environmental hypercapnia on several physiological processes is known. Acute exposure to hypercapnia induces acidosis, which is followed by a compensatory elevation of plasma bicarbonate concentration to restore blood pH to near initial values (Toews, Holeton & Heisler 1983; Cameron 1985). The compensatory phase is accompanied by a reduction in plasma [Cl~-] (Toews etal. 1983; Claiborne & Heisler 1986: Dimberg & Hfglund 1987; Grottum & Sigholt 1996; Fivelstacl, Haavik, Lovik & Olsen 1998), by an increase in plasma [Na~+] (Grottum & Sigholt 1996), possibly to offset H~+ excretion and maintain electroneutrality (Cameron 1985) and by an increase in the O_2 affinity of haemoglob, in (Peyraud-Waitzenegger & 8oulier 1989). Exposure to hypercapnia also induces respiratory and cardiovascular changes, such as increased gill ventilation volume (Janssen & Randall 1975), increased systemic vascular resistance (Perry, Fritsche, Hoagland, Duff & Olson 1999) and an increase of plasma catecholamines in proportion to the severity of blood acidosis (Perry, Kinkead, Gallaugher & Randall 1989). Less information exists about the effect of CO_2 on the performance of cultured fish, although growth may be affected in fish chronically exposed to hypercapnic conditions (Crocker & Cech 1996; Fivelstad etal. 1998). As regards survival during long-term CO_2 exposure, Fivelstad, Olsen, Kloffen, Ski & Stefansson (1999) observed mortality rates of 1.3 percent, 4.3 percent and 7 percent in Atlantic salmon (Salmo salar) smolts held in fresh water at 7, 19 and 32 mg L~(-1) respectively. During shorter-term CO2 exposure, Grottum & Sigholt (1996) indicated the mean lethal concentration (LCso) for sea bass (Dicentrarchus labrax) to be from 115.5 (+- 2.9) to 104.8 (+- 5.1) for exposure periods of 48-120 h. The aim of the present study was to analyse the effect of graded [CO_2] on feed intake and acid-base balance of sea bass held in brackish water.