NUTRIENTS AFFECTING QUALITY IN MARINE FISH LARVAL
DEVELOPMENT
C. Cahu1, J. Zambonino Infante1, and T. Takeuchi2
1. Fish Nutrition Laboratory, INRA-IFREMER, B.P. 70, 29280 Plouzané, France
2. Dep. Aquatic Biosciences, Tokyo University of Fisheries, Minato, Tokyo 108-8477,
Japan
Marine fish larvae undergo major functional and morphological changes during
the developmental stages. For example, the digestive tract develops and matures
during the first week of life and larvae acquire their juvenile morphology and
pigmentation after metamorphosis. Several factors can interfere with the normal
development of larvae and affect quality of larvae produced in hatchery.
Malformations are mainly noted for jaw, gill and spinal cord (scoliosis, lordosis
and coiled vertebral column). Defects in pigmentation can be also considered in
malformations.
It has been demonstrated that genetic or environmental parameters impair
skeletal formation. The influence of diet on larval formation has been
investigated in fresh water species, such as carp, Ayu fish and more recently in
marine species. Some data on the effect of some liposoluble nutrients have been
obtained by using live preys as diet. In particular, the effect of polyunsaturated
fatty acids on pigmentation has been extensively studied in flat fish, such as
Atlantic halibut and Japanese flounder. Nevertheless, though authors generally
believe that highly unsaturated fatty acid of n-6 series (arachidonic and
docosapentaenoic acids) and n-3 series (eicosapentaenoic and docosahexaenoic
acids), as well their ratios, are important for pigmentation, no accurate data on
optimal supply have been determined until now.
Since few years, experimental compound diets have been formulated and allow
undertaking more accurate studies on the effect of different nutrients on
development. Diets inducing harmonious growth in juveniles cannot be directly
used for larvae, since they result in impaired larvae development: poor growth,
high mortality and malformation rate. These effects can be due to nutrients
which concentration and/or nature would be inadequate for young
developmental stages. Lipidic, liposoluble components as well as peptidic
components have been shown to affect larval quality.
Studies conducted on sea bass reported that dietary high phospholipid levels
induce a beneficial effect in marine fish larvae and juveniles. The increase in PL
concentration, from 3 to 12% in a diet specially formulated for larvae led to a
drastic fall in malformed larvae rate, from 35% to 2%. It has been shown in fresh
water species that among phospholipid, phosphatidylinositol is determinant to
prevent skeletal deformities. The assay of brush border membrane enzymes of
enterocytes revealed that phospholipids also play an important role in enterocyte
maturation. Retinoic acid (active form of vitamin A) is a nutrient which role on
development has been clearly established in vertebrates, including zebra fish and
Japanese flounder. Too low or too high levels in retinoic acid perturb the
expression of homeobox genes, which control vertebral axis formation. We
recently investigated the functions of retinoic acid receptors (RAR/RXR) in
craniofacial development during the post-embryonic stage of larval flounder by
using different RAR/RXR agonists. It was demonstrated that the use of retinoid
agonists resulted in lower induce malformations of lower jaw; each retinoic acid
receptor has a different role in lower jaw development during post-embryonic
stage.
Concerning peptidic components, it has been shown that protein hydrolysate has
also a beneficial effect on larval development, when it does not improve or in
some cases depresses juvenile growth. The dietary incorporation of commercial
hydrolysate, such as CPSP (Concentré Protéique Soluble de Poisson,
oligopeptides with 20 amino acid chain length) or experimental hydrolysate such
as short peptides (di- and tripeptides) led to a strong decline in malformed
larvae. The replacement of 50% dietary proteins by hydrolysate induced a
malformation rate four times lower than diet incorporating native protein. The
beneficial effect of hydrolysate has been related to the specific capacity of young
stages to digest and absorb short peptides. These dietary peptides improve
enterocyte differentiation in developing animals. We can assume that this
positive effect on enterocyte differentiation also concern other cells involved in
organogenesis, in particular those involved in antero-posterior axis formation.
Another important observation on improved larval quality concerns dietary
supplementation of taurine. Japanese flounder, red sea bream, yellowtail, and
puffer fish fed more than 1% taurine supplemented diet (containing 1.5-2%
taurine in diet) showed high growth rate and feed efficiency; and in particular
the behavioural characteristics of Japanese flounder resembled the natural fish.