Fatty acid composition of the estuarine amphipod, Melita plumulosa (Zeidler): link between diet and fecundity.

The influence of various diets on the survival, fecundity, and the polyunsaturated fatty acid (PUFA) composition of the benthic estuarine amphipod Melita plumulosa (Zeidler) in laboratory cultures were determined. Apart from a natural silty sediment, six commercial food supplements were examined: an omega-6 PUFA enriched Spirulina-based dry powder, Sera micron; a shrimp-based pellet food; an omega-3 PUFA enriched algal paste, Rotiselco-ALG; an omega-6 PUFA enriched algal dry powder, AlgaMac-ARA (arachidonic acid); flaxseed meal; and an omega-3 PUFA enriched dry powder, Frippak. We have previously established that M. plumulosa cultures perform poorly and eventually decline if provided with silty sediment alone, but will thrive if supplemented with Sera micron. Conversely, if the amphipods are cultured on a nutrient-depleted sand substrate, Sera micron alone does not constitute an adequate feed. The major difference in the fatty acid composition of M. plumulosa cultured on silty sediment compared to amphipods cultured on a sand substrate and both fed Sera micron was an increase in the ratio of omega-3 to omega-6 PUFAs, indicating that the silty sediment provides additional food sources rich in omega-3 PUFAs. Furthermore, amphipods cultured in sand and fed any of the three algal-based foods or the Frippak powder as the sole food source had poor survival rates, although Sera micron maintained the best survival-this was attributed to it containing high amounts of beta-carotene and terpenoids. Melita plumulosa fed a mixture of Sera micron in conjunction with the omega-3 PUFA enriched Rotiselco-ALG and cultured on a silty substrate were found to have good fecundity with low variability.