Contribution to the early life history of Channichthyidae from the Bransfield Strait and South Georgia

Age and early growth of 5 species of Channichthyidae / Champsocephalus gunnari, Chaenocephalus aceratus, Chaenodraco wilsoni, Chionodraco rastrospinosus and Cryodraco antarcticus / were examined. Their postlarvae and juveniles were found numerously in krill catches in the Scotia Sea area during FIBEX /February-April 1981/ and SIBEX /December-January 1983/84/. Additional material - larvae of Chaenocephalus - were collected at the H. Arctowski Station /King George I., South Shetland Is./•from January 1979 to March 1980 /Fig. 1/.
Length frequency distributions of the above-named species were usually unimodal, except for C.gunnari collected off Clerke Rocks /SouthGeorgia/, which length distribution was bimodal, formed by two separate length/age groups /Fig. 2/. Semi-transparent otoliths from postlarvae 38-107 mm SL showed no annuli, which indicates that these fish belong to age group 0. Some periodic patterns of microincrements, discernible in these otoliths under a light microscope, in most cases are considered to be fortnightly /Fig. 3/. Otoliths of juvenile C. gunnari /155-215 mm SL/ had one annulus, approximating in diameter otoliths of C. gunnari postlarvae. Ageing of single juveniles of Chaenodraco, Cryodraco and C. rastrospinosus, stored for some time•in formalin, did not produced satisfactory result.
Average growth rates for Chaenocephalus aceratus and postlarvae /15-40 mm SL/ in the inshore zone of King George I. varied from 0.11 to 0.16 mm per day /Fig. 4/. Growth rates for postlarvae occurring within krill aggregations in the open sea, estimated from modal progressions in size data for Cryodraco, Chaenodraco and C. rastrospinosus were considerably higher, varying from 0.3 to 0.36 mm per day for fish within the 45-100 mm SL length range /Fig. 5,6/. The results obtained demonstrate that larvae of Channichthyidae hatched in September-November become the recruits to the juvenile fish population during the same summer season.
The results presented above, combined with the published data on the length and age of adults, produced the "complete" length frequency distributions /Fig. 7,8,9,10/. It appears from them that C. gunnari from the South Georgia region grow faster in the first two years of life than reported by Sosinski /1981/ and Kochkin /1982/, reaching in April, at the end of a summer season, the total length /TL/ of 7.9 cm in the age group 0 and 19.7 cm TL in the age group I. This growth estimate agrees with the results of Kock /1981/, as well as such estimate of growth of Chaenocephalus through year 1 and 2. Undescribed yet the early growth of the three remaining species seems to be similar to that reported for C. gunnari. and Chaenocephalus. Available data on the age of the adult fish are not complete, but the existing distributions /Gubsch 1982, Skóra - unpubl./, supported by the measurements of otolith length in individual length/age groups /Fig. 11/, allow for the preliminary age-length determination. Thus, the length group 12-18 cm TL of•Chaenodraco /Fig. 9A/ migth be age group I, just as single juveniles 18-20 cm TL of Cryodraco /Fig. 6/, and the length group 20-26 cm TL of C. rastrospinosus /Fig. 10B/ is likely to be age group II.