300
E. A. G. Vidal and S. von Boletzky
et al. 2002a). This is especially true for the enriched Artemia nauplii, which will
contain significantly less nutritional value if not eaten within a few hours of being enriched. Accumulation of low-quality prey items in the rearing tanks can be
avoided by slightly adjusting prey density at every feeding. In addition, prey density
should increase gradually as paralarvae grow at high temperatures as well, when
feeding intake needs to be higher to support the metabolic demand. Hurley (1976)
has estimated a feeding rate of 35–80 % ww day
−1
for D. opalescens paralarvae
reared at 15–17°C.
While prey availability is essential, prey quality is just as important for paralarval
growth. The vital importance of highly unsaturated fatty acids (HUFAs) in the nutrition of marine fish larvae and cephalopod paralarvae is well established (Sargent
1995; Navarro and Villanueva 2000, 2003). As in the case of fish larvae, squid
paralarvae also require food rich in (n-3) HUFA (eicosapentaenoic acid—EPA and
docosahexaenoic acid—DHA). The main lipid classes and the fatty acid composition of the newly hatched L. vulgaris were determined by Navarro and Villanueva
(2000). These authors found that paralarvae are rich in (n-3) HUFA, but particularly
low in (n-6) HUFA, having a very high n-3/n-6 HUFA ratio. They further concluded
that hatchlings need food rich in (n-3) HUFA, phospholipids and cholesterol and
with a reasonable content of neutral lipids.
Thus, the inclusion of prey with high level of (n-3) HUFA, mainly DHA and high
ratios of DHA/EPA is very important in determining dietary value for paralarvae.
Natural preys, such as mysids, decapod crustacean zoeae and marine copepods
(Drillet et al. 2006), have a fatty acid profile very rich in (n-3) HUFA. Their DHA
and EPA content are also very high with a ratio of 1:1 (Navarro and Villanueva
2000). On the other hand, it is well known that Artemia is deficient in long chain
(n-3) HUFA, suggesting that it can cause a nutritional imbalance in the fatty acid
profile (i.e. DHA/EPA ratio) of paralarvae, affecting their survival and growth
(Navarro et al. 1992, Navarro and Villanueva 2000). This implies that to provide
better nourishment as live food for paralarvae, Artemia require HUFA enrichment.
However, recent studies have shown that the supply of juvenile Artemia containing
higher DHA levels was unsuccessful to promote higher survival and growth of
Octopus vulgaris paralarvae during rearing (Seixas et al. 2010). These authors
have found that the protein/lipid ratio, on the other hand, seemed to have a more
important effect on the paralarval growth and survival. This seems meaningful if we
consider that cephalopods metabolism is basically amino acid and protein driven
(Lee 1994). Paralarvae need to synthesize protein at high rates to support their high
growth rates (Vidal et al. 2006). In fact, high levels of the amino acids, lysine, leonine and argentine have been found in L. vulgaris paralarvae, suggesting that they
could be limiting essential amino acids in their diets (Villanueva et al. 2004).
Other studies on the elemental composition of hatchlings and wild juveniles of L.
vulgaris, and on both their natural and artificial prey strongly suggest that they must
demand a food rich in cooper. This is likely related with the haemocyanin requirements for oxygen transport. In addition, S, Na, K, P and Mg were the main elements
found in hatchlings and juveniles (Villanueva and Bustamante 2006). These studies
E. A. G. Vidal and S. von Boletzky
et al. 2002a). This is especially true for the enriched Artemia nauplii, which will
contain significantly less nutritional value if not eaten within a few hours of being enriched. Accumulation of low-quality prey items in the rearing tanks can be
avoided by slightly adjusting prey density at every feeding. In addition, prey density
should increase gradually as paralarvae grow at high temperatures as well, when
feeding intake needs to be higher to support the metabolic demand. Hurley (1976)
has estimated a feeding rate of 35–80 % ww day
−1
for D. opalescens paralarvae
reared at 15–17°C.
While prey availability is essential, prey quality is just as important for paralarval
growth. The vital importance of highly unsaturated fatty acids (HUFAs) in the nutrition of marine fish larvae and cephalopod paralarvae is well established (Sargent
1995; Navarro and Villanueva 2000, 2003). As in the case of fish larvae, squid
paralarvae also require food rich in (n-3) HUFA (eicosapentaenoic acid—EPA and
docosahexaenoic acid—DHA). The main lipid classes and the fatty acid composition of the newly hatched L. vulgaris were determined by Navarro and Villanueva
(2000). These authors found that paralarvae are rich in (n-3) HUFA, but particularly
low in (n-6) HUFA, having a very high n-3/n-6 HUFA ratio. They further concluded
that hatchlings need food rich in (n-3) HUFA, phospholipids and cholesterol and
with a reasonable content of neutral lipids.
Thus, the inclusion of prey with high level of (n-3) HUFA, mainly DHA and high
ratios of DHA/EPA is very important in determining dietary value for paralarvae.
Natural preys, such as mysids, decapod crustacean zoeae and marine copepods
(Drillet et al. 2006), have a fatty acid profile very rich in (n-3) HUFA. Their DHA
and EPA content are also very high with a ratio of 1:1 (Navarro and Villanueva
2000). On the other hand, it is well known that Artemia is deficient in long chain
(n-3) HUFA, suggesting that it can cause a nutritional imbalance in the fatty acid
profile (i.e. DHA/EPA ratio) of paralarvae, affecting their survival and growth
(Navarro et al. 1992, Navarro and Villanueva 2000). This implies that to provide
better nourishment as live food for paralarvae, Artemia require HUFA enrichment.
However, recent studies have shown that the supply of juvenile Artemia containing
higher DHA levels was unsuccessful to promote higher survival and growth of
Octopus vulgaris paralarvae during rearing (Seixas et al. 2010). These authors
have found that the protein/lipid ratio, on the other hand, seemed to have a more
important effect on the paralarval growth and survival. This seems meaningful if we
consider that cephalopods metabolism is basically amino acid and protein driven
(Lee 1994). Paralarvae need to synthesize protein at high rates to support their high
growth rates (Vidal et al. 2006). In fact, high levels of the amino acids, lysine, leonine and argentine have been found in L. vulgaris paralarvae, suggesting that they
could be limiting essential amino acids in their diets (Villanueva et al. 2004).
Other studies on the elemental composition of hatchlings and wild juveniles of L.
vulgaris, and on both their natural and artificial prey strongly suggest that they must
demand a food rich in cooper. This is likely related with the haemocyanin requirements for oxygen transport. In addition, S, Na, K, P and Mg were the main elements
found in hatchlings and juveniles (Villanueva and Bustamante 2006). These studies