No abstract

No abstract

This study assessed the use of extruded feeds, in the form of pellets, for the growing of echinoid Paracentrotus lividus within a closed-culture system. Two feed types, one with soya-bean protein, the other with both soya-bean and ®sh protein were compared with dried Lessonia sp. and fresh Laminaria sp. as food sources. Pellets present a very high conversion eciency (about 80%) against about 50% for Laminaria and 35% for Lessonia. However, as pellets are less absorbed, somatic growth (SG) is statistically equivalent for the sea urchins fed with pellets and Laminaria between 2 and 2.2% g soma day ±1 . Sea urchins fed with pellets produced signi®cantly more gonadal tissue in a shorter time, resulting in a gonadal index (GI) twice higher (6.5%) than Laminaria (3%) in the second month of the experiment. Dry Lessonia does not promote gonadal growth (GG). This study shows that extruded feeds are well assimilated by P. lividus and promote both SG and production of gonadal tissue. KEY WORDS

No abstract

A new growth model is fitted on data from reared sea urchins, Paracentrotus lividus. Quantile regressions are used instead of least-square regressions, because they are insensitive to the dimension of the measurement and accommodate more than just symmetrical distributions. Quantile regressions allow comparison of fittings on various parts of the size distributions, including large competitors versus small, inhibited animals, in the presence of a size-based intraspecific competition. The model has functionally interpretable parameters and allows quantifying of the intensity of growth inhibition. An extension of this model, called "envelope model", fits the whole data set at once, including size distributions. Its parameters are constrained using information about underlying biological processes involved, namely asymptotic growth with inhibition in early ages as the result of intraspecific competition, the intensity of which depends on the relative size of the individual in the cohort. The new model appears most adequate to describe growth of P. lividus and probably many other sea urchins species as well as other animals or plants.