Early development of the head skeleton in Brycon moorei (Pisces, Ostariophysi, Characidae)

At hatching (15 h post fertilization), Brycon moorei possesses no skeletal structure. Thereafter, development is very rapid. The first oral teeth appear no later than 3 It post-hatching, but they remain covered with epithelium until c. 45 h. At 7 h, the trabecular bars and part of the cartilaginous visceral arches are visible and at 15 It, the dentaries and premaxillaries are present. At 25 h, i.e. the onset of piscivory and cannibalism (the yolk sac is only fully resorbed after 36 h), the oral teeth are fully developed, the first pharyngeal teeth are formed, and some head movements already appear synchronized, but the mouth cavity is not completely isolated from the neurocranium by bony structures. Thereafter, no new buccal or pharyngeal bony structure is visible until 45 h, when the maxilla and opercula appear, along with a new type of cannibalistic behaviour. Cartilage resorptions also start at 45 It, but with no concomitant replacement by formation of calcified structures. Later, development gradually becomes similar to that of many previously studied teleosts. The developmental pattern of B. moorei is thus extremely rapid in comparison with other teleosts, i.e. it prioritizes feeding structures that permit the expression of piscivory at a very early age. The uniqueness of this pattern is discussed in relation to ecological constraints on early feeding and fast growth. (c) 2005 The Fisheries Society of the British Isles