Nitrogen budgets for juvenile big-bellied seahorse Hippocampus abdominalis fed Artemia, mysids or pelleted feeds

This study aimed to compare nitrogen budgets for juvenile (1.17 ± 0.07 g, mean ± S.D.) big-bellied seahorses fed live, frozen and pelleted feeds and to examine the potential of non-destructive measurements of excretion to predict feed performance. Three feeds were tested against live Artemia: frozen mysid shrimp species (Paramesopodopsis rufa, Tasmanomysis oculata,Tenagomysis sp.), a pellet prepared from the mysid shrimps and a commercial crumbled feed. Nitrogen budgets were constructed from nitrogen retention measured over a 30 day growth experiment, ammonia and urea excretion measured over 24 h on days 15 and 30, and nitrogen digestibility. After 30 days seahorses fed Artemia and frozen mysid had significantly (P < 0.001) higher final weights and growth than the other two feeds. Although seahorses successfully weaned onto the commercial feed, the final weight was not significantly different from their initial weight. Seahorses fed the mysid pellet were not successfully weaned and lost weight. Feed conversion ratio was significantly (P < 0.001) affected by feed and seahorses fed Artemia and frozen mysid had the most efficient conversion of feed to growth. Despite the poor growth performance of seahorses fed the mysid and commercial pellets survival over 30 days was above 95% and there was no significant difference between treatments. Ammonia excretion was significantly affected by feed on day 15 (P < 0.05) and day 30 (P < 0.001), excretion was higher for Artemia than for mysid pellets on both days. Urea excretion was significantly (P < 0.05) affected by feed only on day 30 and was higher for Artemia and frozen mysids. Nitrogen retention was above 45% on Artemia and frozen mysid treatments. An indirect method of assessing nitrogen retention was an accurate technique where seahorses were growing but not where growth was near or below maintenance. © 2005 Elsevier B.V. All rights reserved.