VARIATIONS IN OTOLITH MICROSTRUCTURE OF SEA-BASS (DICENTRARCHUS LABRAX L.)
LARVAE UNDER DIFFERENT FOOD REGIMES
Aguilera B.*, Palomera I., Olivar M. P.
Institut de Ciències del Mar (CMIMA – CSIC), Passeig Marítim de la Barceloneta 37-49, 08003 Barcelona, Spain
* aguilera@cmima.csic.es, isabel@cmima.csic.es, polivar@cmima.csic.es
Abstract
After validating daily deposition for sea-bass larval otoliths, we found that different feeding regimes did not affect increment deposition
periodicity, although they affected their width. We calculated different condition indices based on otolith microstructure and noticed that,
for the food deprivation experienced by the larvae, all otoliths recovered their size in days.
Keywords: condition index, daily growth, Dicentrarchus labrax, larvae, otolith
Rapp. Comm. int. Mer Médit., 37,2004
305
Sea-bass (Dicentrarchus labrax L.)larvae were reared for the first
month of life under different food regimes [fed, 1 to 3 days of (late)
food deprivation, starved and delayed feeding] to set a condition index
for this species based on the otolith microstructure. Previously, a
marking experiment with alizarine, following the protocol of Blom et
al.(1) was carried out to validate increment deposition.
We observed daily increment deposition beginning the second day
after hatching (Fig. 1). The different food regimes applied did not affect
increment deposition periodicity, but they did affect increment width
(ANOVA, p<0.05). Thus increment width was used for estimating a
condition index (2), which is independent of body size (3).
Starved larvae showed significantly (ANOVA, p<0.05) smaller
otoliths than fed larvae, but no variation in the number of increments
was observed.
Fig. 1. Relationship between larval age and number of otolith increments
in fed larvae. Plotted data are the average counts of both sagittae (n = 155).
When food was supplied to the delayed feeding larvae (i.e., not fed
until the second week of life), a progressive increase of increment
width was observed and after one week of feeding they attained
similar values to those for fed larvae (Fig. 2).
A late food deprivation experiment (i.e., 1 to 3 days with no food)
was conducted on the third week of larval life. We noticed a delay
from the day in which larvae were not fed until it was re?ected on
their otoliths. They formed narrower increments the second day after
the initiation of food deprivation, but they recovered their normal
width the day after they were fed again (Fig. 2).
We calculated a condition index based on the width of the last three
complete growth increments: Recent Otolith Growth Index (4). This
index is based on the residuals between the logarithm of the three outer-
most increments sum and the logarithm of the radii, as a measure of
how much an individual separates from the normal condition (Fig. 3).
Fig. 3. Plotted residuals (Recent Otolith Growth Index) of the fed versus
delayed treatments.
References
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Hamburg.
3-Suthers I. M., 1998. Bigger? Fatter? Or is faster growth better?
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Fig. 2. Absolute increment width of the starved and delayed feeding lar-
vae versus fed larvae.
