The Effects of Plant Protein-Enriched Live Food on Larval Zebrafish Growth and the Status of Its Digestive Tract Development

Live food is necessary for the proper development of zebrafish larvae, providing nutrition in a form that is easily digestible and available to the larvae. Live food is commonly enriched to increase the dietary content of certain nutrients. However, little research has been done on protein-based enrichments, especially those of plant origin. This study sought to examine how different quality protein enrichments affected the composition of live food as well as growth and digestive tract development of larval zebrafish, Danio rerio. Larval zebrafish were fed from 3 to 22 days posthatch (dph) with one of six live food (rotifers Brachionus plicatilis and Artemia spp.) treatments: (1) live food with no enrichment (starved; control); (2) live food enriched with commercially used Spirulina spp. algae; (3) live food enriched with soybean meal (SBM); (4) live feed enriched with soy protein concentrate (SPC); (5) live feed enriched with a fishmeal hydrolysate; and (6) live feed enriched with intact fishmeal (FM). Proximate composition of live food was significantly affected by enrichment, in particular, protein content of rotifers was significantly increased by enrichment with SBM. Zebrafish fed SBM-enriched live food showed longer total body length than all other groups, except SPC. Zebrafish in the SBM group also showed increased gene expression of chymotrypsin in the intestine, possibly indicating improved intestinal development and extracellular digestion, which likely contributed to improved growth. Conversely, zebrafish fed hydrolysate-enriched live food showed reduced gene expression of alkaline phosphatase, possibly indicating a less developed intestinal tract, correlating with reduced growth compared to SBM group. Overall, plant protein was shown to be a promising source of live food enrichment for improving larval zebrafish growth.