Effect of iodine enrichment of Artemia sp. on their nutritional value for larval zebrafish (Danio rerio)

Dietary iodine may play an important role in the nutritional health of freshwater fish larvae. Artemia, commonly used for the culture of larval zebrafish (Danio rerio), contain low concentrations of iodine when compared with wild-caught zooplankton. Iodine concentrations of Artemia can be increased using wax spray beads (WSB) containing potassium iodide (KI; KI WSB); however, the availability of iodine in enriched Artemia for fish larvae is currently unknown. The objectives of this study were to: 1) evaluate the use of KI WSB for enrichment of Artemia with iodine; 2) determine if zebrafish larvae were able to obtain iodine from KI WSB-enriched Artemia; 3) investigate the effects of KI WSB-enriched Artemia on the growth, survival and thyroid status of larval zebrafish; 4) determine if Artemia were a potential source of exogenous thyroid hormones (TH) for larval fish; and 5) determine if KI WSB had an effect on bacterial concentrations associated with Artemia. A 24-day feeding trial was conducted to compare the effects of iodine-enriched Artemia with unenriched Artemia on the survival and growth of larval zebrafish. Zebrafish fed Artemia enriched with KI WSB showed a ten-fold increase in total iodine levels and increased survival when compared with larvae fed unenriched Artemia. Thirty-eight days-post-fertilization (dpf) zebrafish larvae fed iodine-enriched Artemia had lower epithelium to colloid (v:v) ratios when compared to those fed unenriched Artemia. Artemia were found to contain significant levels of outer-ring deiodinase and THs. KI WSB had no effect on the levels of marine bacteria associated with Artemia. The results of this study indicate that iodine contained in KI WSB enriched Artemia is available to larval fish. There was also evidence to suggest that early-stage zebrafish benefit from increased levels of dietary iodine. In addition, Artemia may provide larval fish with significant levels of exogenous THs and deiodinase.