SPATIAL AND SEASONAL PATTERNS IN SPECIES COMPOSITION AND OCCURRENCE OF FISH LARVAE IN THE AREA OF THE CANARY ISLANDS, EASTERN CENTRAL ATLANTIC
¬ CLUPEIFORMES Depending on their yolk sac size, clupeoid larvae hatch at 2 – 5 mm notochord length. Larvae of demersal adhesive eggs hatch at a more developed stage than those of pelagic eggs, but have pectoral fin buds and a continuous finfold present at hatching in common. The sequence of the appearance and ossification of fin rays is headed by the caudal, followed by the dorsal, anal, and pelvic, and ends with the pectoral fin. The fin formation is not fully completed until transformation, which occurs at approximately 20 mm standard length (SL). For identification, counting the number of myomeres or vertebrae is the best tool, however, pigment patterns can be useful, as well. Clupeids can be differentiated from engraulids by the larger gut length and the position of the dorsal to the anal fin. Furthermore, the number of myomeres between those two fins is important for identifying to lower levels within the families. But during metamorphosis the vent, the dorsal and the anal fin migrate forwards relative to the number of myomeres.
-- Reference: OLIVAR and FORTUÑO (1991);
Clupeoidei > Engraulidae In most engraulids the posterior end of the dorsal fin is located over the anterior beginning of the anal fin, which is the most important character leading to this family and easily visible (Figure 27). Engraulids also have a shorter gut than clupeids.
-- References: MCGOWAN and BERRY (1984);
• Engraulis encrasicolus Meristics: Dorsal rays:
14 – 17
Anal rays:
14 – 22
-- Morphology The larvae are elongated with a body depth of only 8 – 9 % of the SL at the level of the pectoral fins. The gut extends to a length of 78 % of SL in early larvae and decreases to 70 % in larvae more than 20 mm SL, but generally terminates between the middle and the end of the dorsal fin. The swim bladder is clearly visible and produces an indentation of the gut. The position of the terminate gut and the fin ray count were confirmed to be of high diagnostic value in this study.
-- Pigmentation In very early developmental stages pigmentation is apparent ventrally between the pectoral and caudal region. A more important marker for identifying is the number of 5 – 8 melanophores on the foregut and 3 – 4 on the swim bladder, which fade away during growth. In larvae of more than 10 mm in length one large spot is found at the anus and up to four more are embedded in the body behind it (Figure 26). Fin pigmentation is only found on the anal fin with a number of 8 spots and a band located posteriorly, but was not visible in the fish larvae examind in this study.
Inf. Téc. Inst. Canario Cienc. Mar. n°13
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