R.O. Cavalli, P. Lavens, P. Sorgeloos
The importance of linoleic acid (18:2n-6) and n-3 highly unsaturated fatty acids (HUFA) on the reproductive performance and offspring quality of the giant freshwater prawn Macrobrachium rosenbergii was evaluated in a 180 day-long trial. Three isonitrogenous, isolipidic diets composed with different fatty acids (diet HH had high 18:2n-6 and n-3 HUFA concentrations; diet HL, high 18:2n-6 and low n-3 HUFA; and diet LL, low 18:2n-6 and n-3 HUFA) were fed ad libitum to three groups of six females. Results showed that fecundity was improved by the addition of higher 18:2n-6 levels (from 3 to 13 mg/g DW), whereas higher n-3 HUFA levels (15 mg/g instead of 5mg/g DW) tended to increase fecundity though this could not be demonstrated statistically. As a consequence of higher fecundity, smaller eggs were obtained probably because the number of oocytes competing for a limited amount of yolk was higher for HH-fed females. Higher gonadosomatic index in HH-fed females further supports this hypothesis. The fatty acid composition of the eggs was a reflection of the diet composition. Eggs from HH-fed females had the highest n-3 HUFA levels and presented an increased hatchability. 8-day old larvae from HH-fed females tended to present a better stress tolerance to ammonia when exposed for 24 h to 100 ppm total ammonia. No further differences were detected among larval characteristics. These results indicate that feeding M. rosenbergii broodstock with high levels of 18:2n-6 and n-3 HUFA (13 and 15 mg/g DW, respectively) improved fecundity, egg hatchability, and the overall quality of the larvae.
(University of Gent, Laboratory of Aquaculture & Artemia Reference Center, Rozier 44, Gent 9000, Belgium)