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Settlement and growth of juvenile fishes of genus Diplodus (Parciformes, Sparidae) in shallow seagrass beds on the eastern Adriatic coast

One year sampling of juveniles of the four sparids from Diplodus sp. were carried out in shallow (between 0.3 m and 5 m depth) meadows of marine phanerograms (Posidonia oceanica, Cymodocea nodosa and Zostera noltii) on several stations in Kornati Archipelago. Data were collected using a 50 m long small beach seine. Observations on the presence and abundance of juveniles were also carried out by using the non-destructive visual census method. Empirical total size-frequency distributions were used for constructing age-length key with 3 mm length intervals and the Gompertz equation was used for juvenile growth estimation. Growth parameters were estimated by the nonlinear least squares method. First settlers of D. annularis, D. vulgaris and D. puntazzo were recorded in July, in January and in November, respectively. For those three species, their juveniles were censused during whole sampling period. D. sargus were censused from June to September. Peak of juvenile densities were recorded a month after first settlers entered in coastal habitats. Thus, those sparids were closely linked to marine phanerogam meadows for settlement. Moreover, those habitats provide to their juveniles shelters and nurseries. Growth parameters as indicators of habitats facilities and specific biological characteristics are as follows: D. annularis (c = 0.042 mm days-1 ; R2 = 0.942), D. vulgaris (c = 0.062 mm days-1 ; R2 = 0.902), D. puntazzo (c = 0.038 mm days-1 ; R2 = 0.832) and D. sargus (c = 0.114 mm days-1 ; R2 = 0.897). Obviously, species, which’ s youngest, spent less time in winter months had higher growth slope. Also, the highest growth of D. sargus is probably tactic of being able to avoid predators and associate to adults as soon as possible. Future studies should attempt to determine to what extent habitat conditions modify the growth pattern of species in different stages of their development.

Settlement; growth; juvenile fishes; Diplodus; Adriatic coast

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