Marine Biology 100, 277-283 (1989) Marine ===BiOlOgy 9 Springer-Verlag 1989 Reproduction of the Antarctic fish Nototheniops nudifrons T.F. Hourigan 1, and R.L. Radtke 2 1 Department of Zoology, University of Hawaii, Honolulu, Hawaii 96822, USA z Hawaii Institute of Geophysics, University of Hawaii, Honolulu, Hawaii 96822, USA Abstract The reproductive biology of the Antarctic fish Nototheniops nudifrons (L6nnberg, 1905) was analyzed by examination of the gonads of fish collected in March and April 1985 in trawls near Low Island, Antarctic Peninsula, and compared to direct observations of reproduction and early larval de- velopment in the laboratory from March to October of the same year. Males and females reached sexual maturity at an age of 4 to 5 yr. Mature males differed in coloration from females and immature males. Ovaries of sexually mature females contained two distinct size modes of vitellogenic oocytes, representing two separate clutches of developing eggs. Females spawned 100 to ~ 3 500 demersal eggs, which were laid in a nest in crevices or under rocks, and guarded by the male for about 4 too. Females did not assist in nest defense or egg care. Most spawning in the field and in the laboratory occurred in late fall and early winter (May to June). A second clutch may be spawned in spring (Novem- ber and December). Eggs hatched after 124 d, and larvae were raised for 38 d. Otoliths of larvae contain internal mi- croincrements, which are deposited in a daily fashion, and are visible by light microscopy. The otoliths of 32 adult fish were examined by scanning electron microscope, and counts of microincrements in these otoliths allowed the back- calculation of hatching dates. Estimated hatching dates were between September and May. Introduction Fishes of the sub-order Notothenoidei evolved in the Ant- arctic and represent the dominant component of the Antarc- * Present address: Laboratory of Reproductive Biology, National Institute for Basic Biology, 38 Nishigonaka, Myodaijicho, 444 Okazaki, Japan tic fish community (DeWitt 1971). Although commercial exploitation of several species has begun, much of their basic biology is still poorly understood (Kock et al. 1985). Studies of the reproduction of Antarctic fishes have concentrated on analyses of gonadosomatic indices, egg counts and sizes at first reproduction. Unfortunately, the data base for even these basic measures is poor (Kock et al. 1985). Many spe- cies reproduce during the winter months, and few studies have been conducted during this time (Sil'yanova 1982a). Most species appear to produce one clutch of large eggs per year (Sil'yanova 1982a). Daniels (1978, 1979) conducted the only study of the reproductive behavior of an Antarctic fish during the win- ter. He discovered a unique system of nest defense by the plunderfish Harpagifer bispinis. Females defend a nest of eggs during a 4 mo incubation period. If the female nest- guard is removed, it is replaced by a male, which will defend the eggs. Although this species has been used as a model for the life-history of Antarctic fishes (Daniels 1983), the gener- ality of this system of reproduction is unknown. Nototheniops nudifrons (formerly Notothenia nudifrons) is among the most abundant demersal fishes in many habi- tats of the Antarctic Peninsula (DeWitt 1971, Targett 1981). Initial gonad analyses suggest that females reproduce once a year during autumn or winter, producing 2 600 to 5 900 demersal eggs (Permiten and Sil'yanova 1971, Sil'yanova 1982a, b). Despite its abundance, information on most aspects of its biology are lacking. Management programs for Antarctic fisheries require knowledge of the biology of both commercial and sym- patric, non-commercial species. As a widespread and abundant species, Nototheniops nudifrons may play a major role in the trophic structure of the Antarctic marine ecosystem, both as a competitor and prey species for com- mercial species. In the present study, the size at reproductive maturity and female fecundity of N. nudifrons were estimated from gonad analyses. Direct observations were made of the reproductive behavior and early larval develop- ment.