Live food enrichments are commonly used to increase the nutritional value of the food, and in this study five protein sources were examined for their effect on larval zebrafish growth and intestinal development : soybean meal (SBM) , soy protein concentrate (SPC), Spirulina algae, fishmeal (FM), and fishmeal hydrolysate.
Enrichments were made by homogenizing the protein source with distilled water and sieved through a 150 μm filter. To enrich live food, equal volumes of either rotifers Brachionus plicatilis or Artemia spp. nauplii were separated into six McDonald jars with aeration and received volumes of enrichment such that total protein in each jar was the same. Larval zebrafish (2 dph) were distributed to 3L tanks with 95 larvae per tank. From 3-22 dph zebrafish were fed ad libitum 4-5 times a day starting with rotifers and later Artemia nauplii enriched with either one of the protein sources or an unenriched control.
Rotifers enriched with SBM had significantly (P < 0.05) higher protein content than unenriched rotifers and rotifers enriched with SPC. This increased protein content at an early age led to increased body length (Table 1) of the zebrafish fed SBM enriched live food compared to all other groups except those fed with SPC-enriched live food. Intestinal maturation and health was assessed through gene expression, which found that chymotrypsin expression in SBM group was significantly higher (P < 0.05) than FM group, indicating a more mature digestive tract which corresponded with higher body length in SBM group. Conversely, zebrafish fed the hydrolysate- enriched live food presented decreased intestinal maturation in larval zebrafish compared to those fed live food enriched with Spirulina or unenriched live food. Administering plant-proteins through enriched live food to larval zebrafish is an effective means of improving growth performance and intestinal maturation during first feeding.