The Ps. georgianus （Pseudochaenichthys georgianus） were sampled in the summer between 1979 and 2009 at South Georgia Island, and at South Shetland Island. The otoliths ofPs. georgianus contained microincrements simi...The Ps. georgianus （Pseudochaenichthys georgianus） were sampled in the summer between 1979 and 2009 at South Georgia Island, and at South Shetland Island. The otoliths ofPs. georgianus contained microincrements similar to daily increments in the otoliths of fishes from temperate and tropical waters. The estimated age from microincrements was similar to that inferred from the body length distribution and otoliths mass： age （years） = 81.98 × Otolith Mass （g） - 0.483. Ps. georgianus like all Channichthyidae due to their adoption to cold water, attain rapidly large body in accordance with the parameters of the von Bertalanffy growth equation： L∞ （asymptotic length） = 66.1 cm; K （constant related to coefficient of catabolism） = 0.28; to （age of the fish at initial length） = 0.008 year; L0 （length of the fish at initial age） = 0.15 cm. That fast growth rate （despite the difference in hatching periods between regions at South Georgia Island, and at South Shetland Island） were not changed, confirming, that it is established to cold water by natural selection. Changes of the microincrements growth pattern are described that appear to be related to larval, hatching and metamorphosis, and have similar pattern to those ones previewed in C. aceratus （Chaenocephalus aceratus） and C. gunnarii （Champsocephalus gunnarii）. Larvaes and postlarvaes of that species have similar habitats during early life history, which is reflected in similar otoliths morphology. Width of their daily increments is： 0.0018-0.0028 mm for Ps. georgianus, 0.0015-0.0024 mm for C. gunnarii and 0.001-0.0016 mm for C. aceratus. The age and developments periods of South Georgia＇s icefish （common name and the abbreviation = SGI for Ps. georgianus as this species was found only there in the past） estimated from otolith was validated by their different geographical distribution depending on the currents and the presence of their food-krill in them. Postlarvae and early juvenile stages were concentrated at the south-western side of the island shelves deeper than 200 m, where currents are weaker in comparison to surface and where juvenes and small krill prevail. Older and mature fish, over 3 or 4 years old, were numerous on the north-eastern side of the islands shelves in regions of strong vortices that concentrate krill to high densities. As life in the currents needs greater ability to swimming as a large, mature and 4 years old fish had increased their ability to swim up to 4 times growing and developing from inshore larvae. During that, their otoliths become more flattened （up to 3 times） and elongated for better fulfil its functions in the higher swimming speed. However, similar species C. aceratus and C. gunnari have more flattened and elongated otoliths than Ps. georgianus and have larger geographical occurrence from Palmer Archipelago to Kerguelen. The least elongated means the highest otolith, which reflects the highest body of Ps. georgianus, which help this species to stay on the shelf during swimming. High body gives less drifting during swimming in the currents. Evolution of otolith shape is linked with a body shape to decrease resistance and achieve high speed of swimming. During development, Ps. georgianus use different currents and countercurrents to catch different krill stages. System of current is natural environment of life ofPs. georgianus.展开更多
文摘The Ps. georgianus （Pseudochaenichthys georgianus） were sampled in the summer between 1979 and 2009 at South Georgia Island, and at South Shetland Island. The otoliths ofPs. georgianus contained microincrements similar to daily increments in the otoliths of fishes from temperate and tropical waters. The estimated age from microincrements was similar to that inferred from the body length distribution and otoliths mass： age （years） = 81.98 × Otolith Mass （g） - 0.483. Ps. georgianus like all Channichthyidae due to their adoption to cold water, attain rapidly large body in accordance with the parameters of the von Bertalanffy growth equation： L∞ （asymptotic length） = 66.1 cm; K （constant related to coefficient of catabolism） = 0.28; to （age of the fish at initial length） = 0.008 year; L0 （length of the fish at initial age） = 0.15 cm. That fast growth rate （despite the difference in hatching periods between regions at South Georgia Island, and at South Shetland Island） were not changed, confirming, that it is established to cold water by natural selection. Changes of the microincrements growth pattern are described that appear to be related to larval, hatching and metamorphosis, and have similar pattern to those ones previewed in C. aceratus （Chaenocephalus aceratus） and C. gunnarii （Champsocephalus gunnarii）. Larvaes and postlarvaes of that species have similar habitats during early life history, which is reflected in similar otoliths morphology. Width of their daily increments is： 0.0018-0.0028 mm for Ps. georgianus, 0.0015-0.0024 mm for C. gunnarii and 0.001-0.0016 mm for C. aceratus. The age and developments periods of South Georgia＇s icefish （common name and the abbreviation = SGI for Ps. georgianus as this species was found only there in the past） estimated from otolith was validated by their different geographical distribution depending on the currents and the presence of their food-krill in them. Postlarvae and early juvenile stages were concentrated at the south-western side of the island shelves deeper than 200 m, where currents are weaker in comparison to surface and where juvenes and small krill prevail. Older and mature fish, over 3 or 4 years old, were numerous on the north-eastern side of the islands shelves in regions of strong vortices that concentrate krill to high densities. As life in the currents needs greater ability to swimming as a large, mature and 4 years old fish had increased their ability to swim up to 4 times growing and developing from inshore larvae. During that, their otoliths become more flattened （up to 3 times） and elongated for better fulfil its functions in the higher swimming speed. However, similar species C. aceratus and C. gunnari have more flattened and elongated otoliths than Ps. georgianus and have larger geographical occurrence from Palmer Archipelago to Kerguelen. The least elongated means the highest otolith, which reflects the highest body of Ps. georgianus, which help this species to stay on the shelf during swimming. High body gives less drifting during swimming in the currents. Evolution of otolith shape is linked with a body shape to decrease resistance and achieve high speed of swimming. During development, Ps. georgianus use different currents and countercurrents to catch different krill stages. System of current is natural environment of life ofPs. georgianus.
