Leptocephalus energetics: assembly of the energetics equation

The principles of energetics were used to examine the energetic requirement s of leptocephali. Respiration and excretion rates and daily growth rates c ombined with proximate composition were used to examine the allocation of e nergy into each of the three main components of energetics: metabolism, exc retion and growth. The daily energetic requirements for leptocephali, refer red to as type 2 larvae based upon their unique developmental strategy, wer e compared to the requirements of non-leptocephalus larvae, known as type 1 . Leptocephalus daily energetic requirements were also compared to the ener gy available from the leptocephalus' proposed food sources. The four specie s of eel larvae selected were all from the order Anguilliformes: Paraconger caudilimbatus (Poey), Ariosoma balearicum (Delaroche), Gymnothorax saxicla Jordan and Davis, and Ophichthus gomesii (Castelnau). The allocation of en ergy to each of the components of energetics as well as the total energetic requirements for the leptocephali proved to be very different from those o f type 1 larvae. Metabolism received the majority, 60-92%, of the energy re quired per day. Growth and excretion were allocated 4-39% and < 1-21%, resp ectively, of the total energy needed per day. Leptocephali required <less t han> 50% of the energy needed by type 1 larvae of equal dry mass. The uniqu e growth strategy used by leptocephali allows them to increase rapidly in s ize while allocating the majority of their energy, not to growth as in most larval fish, but to metabolism.