Abstract.- Sagittal otoliths of 

 the Antarctic fish Nototheniaps nudi- 

 /ro?(.s (F^amiiy Nototheniidae) contain 

 internal microincrements which are 

 visible by scanning electron micro- 

 scopy. Microincrements were depos- 

 ited on a daily basis, as validated 

 through tetracycline and acetazola- 

 mide marking experiments. This was 

 the first validation of daily microin- 

 crement deposition for any Antarc- 

 tic fish. Daily formation of microin- 

 crements continued throughout the 

 year, including during the winter 

 when daylight periods were short. 

 Counts of daily microincrements in 

 the otoliths of 32 juveniles and adults 

 allowed the determination of age and 

 growth rates. From this sample, a 

 multivariate regression model relat- 

 ing fish age to otolith morphometries 

 and fish size demonstrated that age 

 could be estimated reliably from sag- 

 ittal otolith weight and length. Age 

 was estimated for a large sample of 

 N. nudifrons. which allowed the de- 

 termination of growth and natural 

 mortality. Fish grew slowly (1.5 mm 

 per year), reaching sexual maturity 

 at an age of 4-5 years, with the larg- 

 est fish attaining ages of more than 

 8 years. Growth and survivorship 

 were similar for males and females. 



Age and Growth 

 of the Antarctic Fish 

 Nototheniops nudifrons 



Richard L. Radtke 



Oceanic Biology, Hawaii Institute of Geophysics 

 University of Hawaii, Honolulu, Hawaii 96822 



Thomas F. Hourigan 



Department of Zoology, University of Hawaii 

 Honolulu, Hawaii 96822 



The Antarctic fishes are character- 

 ized by a high degree of endemism 

 and extensive adaptations to their 

 unique environment (DeWitt 1971). 

 Ahhough commercial exploitation of 

 several species has begun, much of 

 their basic biology is still poorly 

 understood (Kock et al. 1985). Of 

 special importance to ecological and 

 fisheries research is determination of 

 the age of fish captured in the field. 

 Growth, mortality, and fecundity can 

 be derived from age data. Ageing 

 studies can also provide basic life- 

 history information, such as popula- 

 tion structure, and changes in popula- 

 tion growth due to environmental 

 perturbations. These age-related data 

 increase our understanding of fish 

 biology and form the basis of popula- 

 tion dynamics models. 



Antarctic fishes appear to be slow 

 growing and long lived (Shust and 

 Pinskaya 1978, Freytag 1980a, Kock 

 et al. 1985, Radtke et al. 1989). Al- 

 though age and growth of Antarctic 

 fishes have primarily been deter- 

 mined by counting scale annuli (Olsen 

 1954, 1955; Wohlschlag 1961, 1962; 

 Everson 1970, 1980; Shust and Pin- 

 skaya 1978; and others), the results 

 from this technique are often diffictiit 

 to interpret and especially unreliable 

 for older fishes, as scales may be 

 regenerated or resorbed (Mugiya and 



Manu.sfript accepted 14 May 1990. 

 Fishfi-v Bulletin, U.S. 88:557-571. 



'Contribution Number 2327 of the Hawaii In- 

 stitute of Geophysics. 



Watabe 1977; Freytag 1980a, 1980b). 

 Therefore, an alternative ageing 

 method, such as otolith increment 

 analysis, is desirable. In contrast to 

 scales, otoliths are neither regener- 

 ated nor resorbed, and are the most 

 precise structure for ageing of fishes 

 (Six and Horton 1977, Campana and 

 Neilson 1985). 



Otoliths are calcium carbonate struc- 

 tures deposited in the membranous 

 labyrinth of the inner ear of fish. The 

 otoliths of many fishes grow by daily 

 accretion of layered increments (Pan- 

 nella 1971). These increments are 

 visible in sectioned otoliths as concen- 

 tric rings, which can be enumerated 

 to provide estimates of the age of 

 temperate and tropical fishes (Pan- 

 nella 1971, 1974; Campana and Neil- 

 son 1985; Jones 1986). Otoliths of 

 temperate fishes may also form an- 

 nual increments or annuli. 



Several studies have utilized oto- 

 liths to age Antarctic fishes. Olsen 

 (1955) found that the otoliths of ice- 

 fishes were small and difficult to 

 analyze by light microscopy. Rings in 

 the otoliths of the icefishes Chaeno- 

 cephaluf^ aceratus and Champsoce- 

 phalus gunnari were interpreted to 

 be annuli (Olsen 1955). Subsequent- 

 ly, other researchers used rhythmic 

 patterns in Antarctic fish otoliths for 

 age determinations (Hureau 1966, 

 Everson 1980, Freytag 1980b, North 

 et al. 1980, Mucha 1980, Chojnacki 

 and Palczewski 1981, Kock 1981, 



557 



