PARTICLE RETENTION DURING RESPIRATION AND PARTICULATE FEEDING IN THE SUSPENSION-FEEDING BLACKFISH, ORTHODON MICROLEPIDOTUS

Juvenile blackfish (Orthodon microlepidotus) retained styrene microsph eres (30-90 mu m) during respiration in the absence of food. The fish retained significantly more microspheres when particulate feeding on A rtemia adults, suspension feeding on Artemia nauplii, or in the presen ce of Artemia extract than when respiring in the absence of food. The frequency distribution of microsphere sizes retained during respiratio n did not differ significantly from that retained during feeding, a re sult that is consistent with the hypothesis that the site and method o f particle retention during respiration and particulate feeding do not differ from those operating during suspension feeding. There was sign ificant interindividual variability in the number of particles retaine d. Some individuals retained consistently fewer microspheres than othe r individuals of similar size and age, suggesting that further study i s needed to quantify interindividual variation in other factors (e.g., stroke volume, ventilation rate, or mucus secretion) that have the po tential to affect particle retention rates. Our results have implicati ons for the energetics of suspension-feeding fishes, the impacts of su spension-feeding fishes on plankton communities, and the exposure of t hese fishes to toxic phytoplankton strains and particle-bound organic chemicals.