Biological Oceanography

(^) (After Childress et al. 1980.)
Fish in the general size range examined by Torres et al., with adult length of about
20 cm, all had nearly the same longevity, 4–7 years. However, age at first maturity
tends to increase downward (Childress et al. 1980), with bathypelagic fish
reproducing only at the very end of the life cycle, perhaps only once. Surface fish
reproduce in their second or third season, and mesopelagic fish fall in between.
(^) Childress and colleagues have studied metabolism of mesopelagic organisms over
several decades. Squid (Seibel et al. 1997, 2000), fish (Childress & Somero 1979;
Torres et al. 1979), and large crustaceans (Childress 1975; Cowles et al. 1991) show
decreasing metabolism with depth of habitat (Fig. 12.18). These rates were either
measured at comparable temperatures or corrected for comparability by Q 10 estimates,
so it is nearly certain that rates fall off with depth, due to more than decreasing
temperatures. Further indication that downward cooling is not the sole driver of the
metabolic slowing with depth comes from a comparison of fish metabolism between
the California Current (where there is a strong, vertical temperature gradient), and the
Antarctic (where there is virtually no temperature gradient). In both regions,
metabolism falls off in the same fashion with depth and reaches an asymptotic value
at about 800 m. Childress and Somero (1979) showed that, associated with their
decreasing metabolism with depth, squid, fish, and shrimp have decreasing levels of
both aerobic and anaerobic enzymes in their bodies (or for some measures just in
muscles). It is argued from this that the metabolic-rate reductions are almost certainly
real and not attributable to damage by collection procedures and retrieval from depth.
Fig. 12.18 Respiration rates measured as oxygen consumption in fish (diamonds),