Nutritional and bacterial profiles of juvenile Artemia fed different enrichments and during starvation

Biochemical and bacterial profiles of juvenile Artemia (1.5 mm, 5 days old) were examined in two experiments designed to manipulate their nutritional composition. In Experiment 1, Artemia were enriched for up to 36 h with the diatom Chaetoceros muelleri, the chromist Schizochytrium (Algamac 3050) or a squid oil emulsion. In Experiment 2, Artemia were enriched with the same diets for 6 h, and then starved for 24 h at 4, 18 or 28 degrees C. Artemia did not survive beyond 24 h enrichment on Algamac and survival was low on oil emulsion, contrasting with the rapid growth and high survival on C. muelleri. Fatty acid (FA) content of Artemia increased marginally after enrichment with C. muelleri, with a marked increase over 36 h enrichment in the percent long-chain polyunsaturated FA (LC-PUFA). FA content increased by 60% and 140% after enrichment with Algamac and squid oil emulsion, respectively, and %LC-PUFA also increased. FA content and %LC-PUFA in starved Artemia declined by up to 57% at 28 degrees C whereas the proportional loss was < 30% at 4 degrees C. Ascorbic acid (AsA) content in Artemia increased four-fold over 36 h enrichment with C. muelleri and declined or did not change with the other enrichments. AsA was retained during starvation of 6 h-enriched Artemia with all treatments. alpha-Tocopherol (alpha-T) concentration increased three-fold to a peak after 6 h on oil emulsion and increased two-fold after 24 h on C. muelleri while decreasing by 50% during 12 h on Algamac. alpha-T declined during starvation by up to 50% (depending on temperature) following enrichment with oil emulsion although there was no change with C. muelleri or Algamac. For Artemia enriched 12 h on C. muelleri or 6 h on oil emulsion, bacterial abundance was not elevated but further enrichment resulted in increases by two- to three-fold. Bacterial abundance in Artemia enriched for 6 h on Algamac increased four-fold and by 24 h, most Artemia had perished. Total numbers of heterotrophic bacteria and Vibrio spp. were similar after enrichment for 6 h with C. muelleri or oil emulsion and after 24 h starvation at 18 or 28 degrees C. Starvation at 18 or 28 degrees C after Algamac enrichment increased bacterial numbers up to four-fold. For Artemia starved at 4 degrees C for 24 h, there was a marked reduction in bacterial numbers for all enrichments, indicating that cool temperatures may be bactericidal. Enrichment of juvenile Artemia for 6 h achieved substantial biochemical improvement while minimising bacterial contamination, and is regarded as a suitable protocol before feeding to target species such as spiny lobster phyllosoma larvae.