Spawning and early ontogenesis in channel bull blenny Cottoperca gobio (Notothenioidei, Perciformes) caught off the Falkland Islands and maintained in captivity

The channel bull blenny Cottoperca gobio (Notothenioidei, Perciformes) is the largest species of the family Bovichtidae that inhabits both the shelf and upper slope around the southern tip of South America. It is a common non-retained bycatch species during finfish bottom trawl fisheries on the Patagonian Shelf in the Southwest Atlantic. The present study aimed to address previously unknown aspects of its spawning, egg development and early larval growth by maintenance of adults in an aquaculture facility. The fish spawned in the beginning of austral spring (early September), adhering the eggs to the wall of the tank in a band of about 120 cm long, and 20–25 cm wide, estimated to contain ~170,000 eggs. Before and after spawning, the body colouration of both sexes changed displaying marked sexual dimorphism. The male did not guard the spawning site. Egg sizes varied between 2.1 and 2.4 mm. Eggs had a characteristic oil droplet inside. Embryogenesis lasted 50 days, constituting 305 accumulated degree-days. Newly hatched larvae were 7.8–8.1 mm total length, having the oil droplet inside their yolk sac. The yolk sac feeding period lasted approximately 9 days. Anterior part of the larval body was heavily pigmented such that pigmentation could be used for identification purposes. C. gobio occupied the very r-end of the r/K continuum among demersal notothenioid fish, characterised by high fecundities, small eggs and larvae, lack of parental care and high growth rates enabling it to populate the vast areas of the Patagonian Shelf whilst competing with other abundant large demersal fish predators.

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