Age determination and validation studies of marine fishes: do deep-dwellers live longer?

Age determination and validation studies on deep-water marine fishes indica te they are difficult to age and often long-lived. Techniques for the deter mination of age in individual fish includes growth-zone analysis of vertebr al centra, fin rays and spines, other skeletal structures, and otoliths (th ere are three sets of otoliths in most bony fish semicircular canals, each of which is made of calcium carbonate). Most have regular increments deposi ted as the fish (and its semicircular canals) grows. The most commonly used otolith for age determination is the largest one called the sagitta. Age v alidation techniques include: (1) tag-recapture, often combined with oxytet racycline injection and analysis in growth-zones of bone upon recapture; (2 ) analysis of growth-zones over time; and (3) radiometric approaches utiliz ing a known radioactive decay series as an independent chronometer in otoli ths from bony fishes. We briefly summarize previous studies using these thr ee validation approaches and present results from several of our radiometri c studies on deep-water, bony fishes recently subjected to expanding fisher ies. Radiometric age validation results are presented for four species of s corpaenid fishes (the bank, Sebastes rufuss, and bocaccio, S. paucispinis, rockfishes, and two thornyhead species, Sebastolobus altivelis and S. alasc anus). In addition, our analysis of scorpaenids indicates that longevity in creases exponentially with maximum depth of occurrence. The reason that the deep-water forms of scorpaenid fishes are long-lived is uncertain. Their l ongevity, however, may be related to altered physiological processes relati ve to environmental parameters like low temperature, high pressures, low Li ght levels, low oxygen, and poor food resources. (C) 2001 Elsevier Science Inc. All rights reserved.