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

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.