GOODING ET AL.: RESPIRATION RATES AND LOW-OXYGEN TOLERANCE IN SKIPJACK TUNA 



sible, we built a smaller respirometer for the nine 

 subsequent series of experiments. 



The smaller respirometer consisted of a fiber 

 glass tank, elliptical in the horizontal plane; it 

 held 2,400 1 of water and was 2.44 m long by 1.83 

 m wide by 0.61 m deep (Figure 1). The top edge of 

 the tank had a 5.0 cm wide lip to which was 

 cemented a 0.9 cm thick sponge-neoprene gasket; 

 on this gasketed lip, there was seated, and firmly 

 clamped, a rigid cover made of 0.4 cm thick 

 transparent acrylic plastic strengthened by three 

 10 cm wide strips of 6.5 cm thick marine plywood 

 cemented to its outer surface. A short length of 5 

 cm PVC pipe, which served as a vent and access 

 port, was tapped vertically through the plastic 

 and plywood in the center of the cover. Glued 

 flush with the inside surface of the acrylic, the 

 pipe extended about 8 cm above the water level. 



An inlet and drain allowed fresh sea water to 

 flow through the chamber at rates up to 190 1/min. 

 Both inlet and drain were valved. By slightly 

 overfilling the chamber before closing the inlet 

 valve, we caused the acrylic cover to bulge up- 

 ward 4 cm at the center. The domed conformation 

 permitted the easy removal of bubbles from the 

 chamber through the vent pipe. A sponge rubber 



ball, fitted snugly into the pipe during experi- 

 ments, completed the seal. 



Both respirometers were illuminated with 

 overhead fluorescent lights. Indirect natural 

 light coming through windows and doors was 

 not excluded. Visibility of fish in the smaller 

 respirometer was excellent, permitting detailed 

 observation of fish speed and behavior during 

 an experiment. 



Dissolved oxygen measurements in both res- 

 pirometers were made with a YSI^ model 51A 

 oxygen-temperature meter coupled with a YSI 

 model 5418 oxygen-temperature probe. For mea- 

 surements in the larger respirometer, water was 

 electrically pumped between the tank and a small 

 acrylic chamber in which the probe was mounted. 

 In experiments involving the smaller respirom- 

 eter, the oxygen-temperature probe was placed 

 inside the tank through the vent pipe in the 

 cover. The probe was vigorously jiggled for about 

 15 s before each reading of the meter; during the 

 intervals between readings, a sponge rubber ball 



^Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA, or by Texas 

 A&M University. 



2 m STICK 



CLEAR ACRYLIC TOP 



7.5 cm DRAIN 



Figure l. — The small sized respirometer used in oxygen-uptake experiments 2-10 on skipjack tuna. 



33 



