IMPORTANCE OF BROODSTOCK NUTRITION IN WHITE SHRIMP
LITOPENAEUS VANNAMEI
PhD thesis by Roeland Wouters
Faculty of Agriculture and Applied Biological
Sciences, Ghent University, Belgium, 195 pp.
Table of Contents:
Summary:
Currently, our knowledge on the nutrient requirements
for shrimp during ovarian maturation and reproduction is insufficient to
develop performing artificial broodstock diets. Maturation systems still
rely on fresh food organisms like molluscs, crustaceans and bloodworms for
optimal reproductive output. Unfortunately, fresh food carries along
acquisition and storage problems, high cost, increased risk of disease
transmission, and water fouling among others. Improving the knowledge on
broodstock nutrient requirements and optimising feeding practices for the
marine penaeid shrimp Litopenaeus vannamei (Boone 1931) were thus the
principal objectives of the present work.
One of the first activities in this thesis was the
characterisation of the composition of total lipids, fatty acids, lipid
classes, and levels of vitamin C and E in tissues of wild females and the
description of the changes that occur in these components during ovarian
maturation and upon spawning (Chapter III). The biochemical composition of
nauplii from wild females was also documented. This work provided important
baseline data and allowed deduction of the role of specific nutrients in
shrimp reproduction. Triacylglycerol (TAG) and phophatidylcholine (PC) were
the dominant lipid classes. In the ovaries, the free fatty acids (FFA)
prevailed. High concentrations of arachidonic acid (ARA; 20:4n-6),
eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3)
were found in all tissues. The most important change during ovarian
maturation was the increase of total lipids (TL) in the ovaries, and
subsequent decrease in the hepatopancreas. The levels of vitamins C were
high in the ovaries, but low in the nauplii. The levels of vitamin E
increased substantially during ovarian maturation and were high in the
nauplii.
In a first large-scale reproduction experiment
(Chapter IV), the effect of co-feeding Artemia biomass and enriched Artemia
biomass on the reproductive performance and offspring quality was evaluated.
The control treatment consisted of a mixture of squid, mussel, clam and
oyster. Co-feeding non-enriched Artemia biomass resulted in higher survival,
higher maturation frequency, a better multiple spawn performance and an
improved offspring quality. The best results were obtained by co-feeding
enriched Artemia biomass. In a subsequent experiment, the relative
importance of the Artemia enrichment fractions was studies: the lipid
fraction rich in n-3 highly unsaturated fatty acids (n-3 HUFA) and
cholesterol, versus the vitamin fraction rich in vitamin E, vitamin C and
astaxanthin. It was demonstrated that the lipid fraction is the most
effective one, though Artemia enrichment with the sum of both fractions
gives the best results.
The results of Chapter III and Chapter IV suggested
that HUFA are not required in high levels for normal ovarian maturation.
This was confirmed by the diet-response experiment reported in Chapter V:
different dietary HUFA levels do not affect ovarian maturation. Total
dietary lipid levels (TDL), on the other hand, have a clear influence on
ovarian maturation. A decrease of the gonadosomatic index was observed by
increasing TDL levels from 8.1% to 8.8% or above.
In Chapter IV, the effect of freeze-dried Artemia
biomass as an ingredient of artificial diets was evaluated on wild and on
pond-reared shrimp in a two-factor design. The inclusion of freeze-dried
Artemia resulted in an increased diet intake, ovarian maturation and spawn
performance. Some additional effects were obtained in pond-reared shrimp. A
different performance and different response to the diet between wild and
pond-reared broodstock was observed.
The possibility of substituting 50% of the fresh food
ingredients typically used in maturation systems world-wide was studied in
Chapter VII. In the first experiment, the artificial control diet and the
artificial diet with freeze-dried Artemia biomass inclusion outperformed the
100% fresh food treatment. In experiment 2, performed in a commercial
maturation facility, the treatment with the artificial control diet and the
100% fresh food treatment did not differ in any of the evaluated parameters.
The artificial diet with freeze-dried Artemia biomass inclusion fed at a 50%
substitution rate resulted in better spawn performance, higher egg
production per female and better spermatophore quality.
In conclusion, the findings of this thesis
demonstrate that an improved diet can enhance the performance of Litopenaeus
vannamei broodstock shrimp as well as the quality of their offspring.