Carotenoid-enriched microalgal biomass as feed supplement for freshwater ornamentals: albinic form of wels catfish (Silurus glanis)

Abstract

Experiments were aimed at examining the effect of carotenoid-rich microalgal biomass as feed supplement to increase the colouration of a freshwater ornamental fish species – an albinic form of wels catfish (Silurus glanis). We used four Algadiets (AD 1, AD 2, AD 3, AD 4 – various Algadiets prepared by addition of microalgal biomass to a basal diet) made up of a basal diet supplemented with 25 g kg−1 spray-dried biomass of green algae Scenedesmus, Chlorella, or Haematococcus enriched in carotenoids (12–60 mg kg−1 of feed) for a juvenile fish (yearlings; about 14–25 g and 12–15 cm) in indoor tanks. In 2-month experiments, the fish groups were examined at 20-day intervals. In the treatment groups fed with Algadiets, the specific growth rate and physical condition index (weight/length) increased by 11–58% and 6–26%, respectively, compared to the control (fed on the basal diet). Skin colouration was evaluated from digital images. An intensive yellow or yellow–orange colouration appeared in all Algadiet-fed fish groups because colour saturation increased 1.4–2.4 times within 20–40 days of the trial. A change from an albinic to an intensive ‘golden’ colour was visible as the shorter-wavelength shift from 595–607 to 584–586 nm. These results are economically valuable for albinic catfish breeding, a unique and commercially important species for fisheries in the Czech Republic.