Chemical composition and growth indices in leptocephalus larvae |
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Authors: | R E Bishop J J Torres R E Crabtree |
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Institution: | (1) University of South Florida, Marine Science Department, 140 Seventh Avenue South, St. Petersburg, Florida 33701, USA Fax: 001 (0)727 553-1189 e-mail: rbishop@marine.usf.edu, US;(2) National Marine Fisheries Service, Southeast Regional Office, 9721 Executive Center Drive, St. Petersburg, Florida 33702, USA, US |
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Abstract: | Leptocephali grow at extremely high rates (>1 mm d−1), but, unlike most fish larvae, leptocephali may remain in the plankton as larvae for several months before metamorphosing
into the juvenile form. During their planktonic phase, leptocephali accumulate energy reserves in the form of glycosaminoglycans
which are then expended along with lipid reserves to fuel metamorphosis. Otolith growth rates were determined using scanning
electron microscopy for four species of leptocephali common in the Gulf of Mexico, Paraconger caudilimbatus (Poey, 1867), Ariosoma balearicum (Delaroche, 1809), Gymnothorax saxicola (Jordan and Davis, 1891), and Ophichthus gomesii (Castelnou, 1855). Proximate composition, RNA:DNA ratios and protein growth rates were examined with respect to mass, length
and age. The leptocephalus growth strategy was strongly reflected in the growth indices. Mass (Y) in all four species increased with increasing age (X) according to the equation Y = aX
b
, where a is a species-specific constant and 1.05 < b < 2.40. The accumulation of acellular mass was evident in protein growth rates and RNA:DNA ratios, and was observed as a
shift in increasing size from rapid growth in length to a greater increase in mass with age. These results suggest that the
proportion of actively metabolizing tissue declines with size and is replaced by the metabolically inert energy depot: the
glycosaminoglycans. Leptocephali can thus grow to large size very rapidly with minimal metabolic penalty, an unusual and successful
developmental strategy.
Received: 27 December 1999 / Accepted: 8 June 2000 |
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