production and
nutritional adaptation of the brine shrimp artemia sp. as live food organism
for larvae of marine cold water fish species
PhD
Thesis by Jan Ove Evjemo
Norwegian University of Science and Technology,
Faculty of Chemistry and Biology, Trondheim, Norway, 2001,
ISBN: 82-471-5050-6
Conclusions:
A. franciscana feeding on different concentrations of
algae increased the ingestion rate as a function of food concentration up to
a saturating level. Further increase of the food concentration did not
effect the ingestion rate. Different stages of A. franciscana showed a type
3 functional response.
The assimilation rate of A. franciscana was high at
saturated food concentrations (10-15 mg C/l) and decreased at higher
concentrations of algae (20 and 30 mg C/l). Assimilation efficiency (%) was
high at low food concentrations and decreased at higher concentrations.
The growth rate of A. franciscana reached an optimum
at saturated food concentrations. At lower concentrations the growth
decreased successively as a function of algal concentration. A. franciscana,
fed saturated food concentrations, showed significantly changes of the
growth rate when the animals developed from nauplii the adult stage. In the
exponential part the growth cycles the individual dry weight might increase
from 2 until 3 times per 24 h. Based on these results there is a wide range
of possibilities to manipulate the size of A. franciscana and thereby
provide the most ideal size of the live food organism for the fist larvae.
DHA accumulates at a high rate during enrichment of
A. franciscana but the high loss rate of DHA after enrichment might be a
problem. It is important to establish careful routines post enrichment that
allow transfer of A. franciscana to the fish tanks shortly after enrichment.
Short residence time of the live food in the fish tanks will reduce DHA
catabolism. If A. franciscana must be stored this should take place at a
relatively low temperatures (<6°C).
The loss rates of the lipid and protein content after
enrichment increased with increasing temperature. The total lipid content
decreased at a higher rate than the protein content and DHA became reduced
at a considerably higher rate than EPA. The nutritional value of A.
franciscana might be significantly reduced when residence time between end
of enrichment and larval consumption increase.
The non-commercial Chinese strain, Artemia sinica,
retained a high DHA level post enrichment and was less affected by the
temperature than A. franciscana. This might indicate that the catabolism of
DHA is genetically determined.
The total protein content in Artmeia sp. might be at
an acceptable level for marine fish larvae of the cold water fish species,
whereas the lipid level must be modified through enrichment with emulsified
lipids.
There were significant differences in the lipid
content and the distribution of fatty acids in the marine copepods examined
and enriched A. franciscana. The copepods were characterised by a relatively
low lipid content and a high content of n-3 HUFA. A.franciscana had higher
lipid content and a lower n-3 HUDA content. Through proper enrichment diets
the n-3 HUFA content in A. franciscana can be significantly increased. By
introducing new enrichment diets, particularly developed for Artemia sp.
when used as live food organism for marine cold water fish species, the
nutritional value of Artemia sp. might reach the requirements of the fish
larvae.
There was a close relationship between the percent
DHA content in the halibut larvae and in different live food organisms fed
to the larvae. High DHA content in the live food organism was reflected by a
high DHA content in the larvae and vice versa. The DHA content in the larvae
was significantly reduced after 8 days of feeding when the live food
organisms used had a relatively low DHA content.
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