Abstract
This study describes the egg membrane structures of angelfish (Pterophyllum scalare), morpho-physiological changes during angelfish embryogenesis from activation to hatching under optimal conditions (28°C; pH 6.8), the developing larvae and fry, the effect of alkaline pH on the early developmental stages of the species, the relationship between food item size and fry survival. Egg membranes (thin, transparent, 1.67-2.18 µm thick) are covered by a sticky substance. The amber-coloured angelfish eggs were oval in shape, with average diameters of 1.436 and 1.171 mm, i.e., a mean volume of 1.033 ± 0.095 mm³. The survival rate of embryos and larvae kept in water with an elevated, slightly alkaline pH was very low: as few as 2% of the embryos survived, while in the batch kept in optimal water conditions very few eggs died. The first larvae hatched after 1288 h of embryonic development. The newly hatched larvae measured on average 2.60 ± 0.093 mm and had large (0.64 ± 0.077 mm³) yolk sacs. They attached themselves to the substrate with a secretion of thin, viscous threads, which was released from glands situated on the top of the head. The glands vanished on day 5. The 1-day-old larvae showed the first pigment cells on the body and the eyes of the 2-day-olds were already fully pigmented. Between day 4 and 5 of larval life, the larvae began feeding on live food. The 23-day-old fry looked like a miniature versions of the adults. Mortality of the angelfish larvae during their first days after hatching was higher in those fed brine shrimp (Artemia salina) nauplii than those fed protozoans and rotifers.
Highlights
Angelfish occur in the catchment of the Amazon, the world’s largest river; they inhabit waters having uniform, albeit specific, chemical and physical conditions in Brazil, Columbia, Peru, Guyana, and French Guyana (Axelrod & Walker, 2000; Pérez et al, 2003; Abdolbaghian et al, 2010)
The research focused on the developing eggs and the resultant larvae of the angelfish (Pterophyllum scalare)
The egg membrane was porous on the inside, individual pores were very small
Summary
Angelfish occur in the catchment of the Amazon, the world’s largest river; they inhabit waters having uniform, albeit specific, chemical and physical conditions (e.g., temperature 27-30°C; pH ~6.5) in Brazil, Columbia, Peru, Guyana, and French Guyana (Axelrod & Walker, 2000; Pérez et al, 2003; Abdolbaghian et al, 2010). Angelfish live usually at the depth of 1-2 m, among dense, submerged vegetation (Frank, 1984). Under natural conditions, they grow to 15 cm total length and 25 cm total height. Angelfish are characterised by specific reproductive behaviour. The territory occupied by the male is of crucial importance: the female chooses a partner based on the specificity of a male’s territory, e.g. the plant species growing
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