Spawning, egg development and early ontogenesis in rock cod Patagonotothen ramsayi (Regan, 1913) caught on the Patagonian Shelf and maintained in captivity
Rock cod Patagonotothen ramsayi (Regan, 1913) is one of the most abundant fish of the family Nototheniidae inhabiting the Patagonian Shelf and upper Slope in the southwest Atlantic. Recently, P. ramsayi became an important commercial species around the Falkland Islands with annual catch of 60,000–75,000 t. The present study aimed to reveal previously unknown aspects of reproductive biology of P. ramsayi during the first successful maintenance of adults for more than a year in an aquaculture facility with running seawater. The fish spawned at the end of austral winter. During spawning, males changed their coloration dramatically, occupied artificial shelters on the bottom and showed aggressive territorial behaviour. Egg masses were light-yellow to light-orange irregular spongiform. They were negatively buoyant, but located outside shelters and were ignored by males. Egg diameters varied between 2.1 and 2.3 mm, and the number of eggs per egg mass ranged from 26,800 to 123,400. Embryogenesis lasted 28–32 days. Total lengths of newly hatched larvae ranged from 6.2 to 6.7 mm. The yolk sac feeding period lasted approximately 11 days, during which the larvae showed negative phototaxis. One-month-old larvae attained 8.8–9.0 mm in length. This study confirms that P. ramsayi exhibit the reproductive strategy typical for nototheniid species occupying low-latitude peripheries of their distributional range, characterised by a combination of r-features (small eggs and larvae, high fecundity) and K-features (territorial behaviour and possible nest guarding).
KeywordsPatagonotothen ramsayi Spawning Egg mass Embryogenesis Southwest Atlantic
We are grateful to L. Jurgens and Z. Shcherbich for collecting and transporting live fish to the aquaculture facility and to scientific observers from the Falkland Islands Fisheries Department, especially D. Davidson and A. Monllor, who helped in maintaining the fish tank and looking after the fish. We are thankful to S. Brown (Shallow Water Marine Group, Stanley, Falkland Islands) for photographing live fish in the tank. We thank our colleagues Drs A. Winter, P. Brewin and V. Laptikhovsky for their comments and suggestions that helped to improve the manuscript. We also thank the Director of Natural Resources John Barton for supporting this work.
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