Energetic Cost of Suspension Feeding versus Particulate Feeding by Juvenile Sacramento Blackfish

Abstract

All species of suspension-feeding teleost fishes switch from particulate feeding to suspension feeding at a standard length of about 2–5 cm. Although this ontogenetic shift in feeding mode is suggestive of an energetic or biophysical constraint that restricts small fishes to particulate feeding, there have been no comparisons of the energetic costs of pump suspension feeding and particulate feeding based on oxygen consumption data. We found that the O2 consumption (mg O2/[g body weights·h]) associated with the capture of prey by juvenile Sacramento blackfish Orthodon microlepidotus (Cyprinidae) during pump suspension feeding on small zooplankton did not differ significantly (P > 0.05) from that measured during particulate feeding on large zooplankton. The metabolic cost of energy acquisition (mg O2/[g body weights·103 J prey consumed]) was approximately 2.5 times higher (P ≤ 0.02) for pump suspension feeding than for particulate feeding. However, because the actual energy expenditure during the feeding period was only about 2% of the energetic content of the Artemia nauplii consumed during suspension feeding and less than 1% of the energetic content of the Artemia adults consumed during particulate feeding, the advantage of particulate feeding may be a potentially high rate of energy intake rather than a low energy expenditure. Because suspension feeding provides a lower rate of energy intake, small fishes may be unable to obtain the energy required for growth and maintenance by this feeding mode.