(^) Mauchline (1988), in commenting on the results of Childress et al. (1980), noted
that their data were viewed on a year-by-year basis. Roughly annual growth rings
(annual annuli) are, however, evidence that growth varies seasonally. Mauchline
developed some month-by-month growth estimates based on size–frequency analysis
for mid-water fishes in the Rockall Trough, confirming this seasonality in growth for
a number of species. As also shown by the shrimp growth data, seasonality telemeters
down the water column, not fully damped by the constancy in temperature, salinity,
oxygen, and other physical factors. Bathypelagic fish, on the other hand, showed no
seasonal changes in growth rates. The vertical telemetering of seasonality is an active
area of research.
Energy Utilization Is Extremely Efficient
(^) Childress et al. (1980) determined the mean masses for fish of known ages, presenting
the results as curves of caloric content versus age (Fig. 12.16). Those mesopelagic
fish that migrate into surface layers at night grow in body mass in the same pattern as
do epipelagic fish, for example sardines. They have the same proportional weight
increase with age, although they have a smaller initial size, placing their curves far
below that of the sardine. It is hard to find a perfect comparison, since most mid-water
fish are taxonomically distant from surface species and are smaller. Growth of
bathypelagic fish, species confined to deep layers and short rations, slows less
strongly than that of mesopelagic species, and is close to continuously exponential.
They grow both faster and larger than mesopelagic fish. Data for Poromitra
crassiceps are amazing; growth is perfectly exponential for 7 years! A reviewer of this