Morphology of gill rakers and their ecological function in feeding of the Antarctic fish Notothenia neglecta Nybelin

Abstract

Notothenia neglecta, endemic to the Antarctic and sub-Antarctic regions, is basically carnivorous with a wide dietary spectrum. In order to evaluate the gill rakers' morphology and histological features of gill structures in relation to their feeding habits, specimens were obtained at Admiralty Bay (King George Island, South Shetlands). Their stomach content was identified and measured and the pharyngobranchial apparatus was studied macro and microscopically. The morphology of the gill rakers and the sizes of prey that are present in the stomach of N. neglecta characterize this species as piscivorous but also able to capture other small prey. Gill rakers provided with sharp villiform denticles improve the retention of fish. At the anterior row, gill rakers are flexible and without denticles, allowing continuous breathing during slow ingestion of large prey. Food is selected by size. The distance between gill rakers allows the retention of amphipods, bivalves and gastropods if bigger than 0.17% of the predator standard length. Food is also selected chemically by taste buds and isolated chemical-sensorial cells. Goblet cells produce mucus that covers the preys with a smooth layer, avoiding scratching of the mucosa during ingestion of food and promoting aggregation of smaller food items. N. neglecta is an active feeder that uses different detection and selection mechanisms to survive in an environment where the food composition varies during the year.