chapter reasonably suggested that minimal movement and flaccid, low-maintenance
muscles allow a higher portion of acquired food to be routed to growth.
Fig. 12.16 A comparison of growth curves (body mass as caloric content) vs. age for
epipelagic fish (sardine, ×), mesopelagic migrators (open symbols), and
“bathypelagic” species (solid symbols). The solid hexagons are for Poromitra
crassiceps, which has a very unusual growth pattern.
(After Childress et al. 1980.)
Oxygen consumption estimates (Torres et al. 1979) for fish captured with insulated
cod-ends, can be interpreted in terms of metabolic energy expenditure. Metabolism is
very strongly reduced in mid-water fish compared to surface fish of comparable sizes
at a given age. Mesopelagic migrators use about 25% of the energy used by surface
fish, whereas bathypelagic species use less than 10%. Combining growth data with
metabolic data, estimates can be made of the relative growth efficiencies of mid-water
and epipelagic fish (Fig. 12.17). Since energy consumption for swimming and tissue
maintenance declines with depth, growth efficiency of deep-living fish can be and is
higher throughout life. The 60–70% growth efficiency of young bathypelagic fish is
astoundingly high compared to that of terrestrial or epipelagic animals. Similar
growth characteristics probably pertain for all mesopelagic animals, particularly
squids and shrimp.
Fig. 12.17 Growth efficiency of fish as a function of age compared for sardine (×),
mesopelagic migrators (open circles) and bathypelagic species (•). Numbers in
parentheses are sample sizes. The term “partial growth efficiency” is used because
food ingested but not assimilated is not accounted for.