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.

Effects of applying nutritional programming at different early stages of Largemouth bass (Micropterus salmoides, Lacepède) development on growth and dietary plant protein utilization.

Plant protein (PP) utilization in fish is limited due to lower digestibility compared to fishmeal (FM) and the presence of antinutritional factors. Its utilization can be improved by nutritional programming (NP), a method wherein a fish is provided a nutritional stimulus early in life which can alter their physiology. NP has been shown to be effective but methods of applying NP are varied and have been applied at different stages of development with different outcomes. To find the optimal timeframe to perform NP in fish early stages Largemouth bass (Micropterus salmoides, Lacepède) were nutritionally programmed at three different ages in early development. In this study bass were programmed with: (1) live food enriched with soybean meal (SBM) from 6 to 15 days post-hatch (dph) (NPL), (2) SBM-based formulated diet from 16 to 25 dph (NPD1) and (3) formulated SBM-diet from 26 to 35 dph (NPD2). After programming, each group was fed FM-diet before being refed SBM-diet from 100 to 172 dph. A positive control (PC) was fed FM-diet throughout. Final average body weight of PC was significantly higher than NPD1 and NPD2 but did not significantly differ from NPL. Overall NPL showed much improved growth and utilization of PP compared to NPD1 and was similar to growth achieved by PC. This study showed an optimum window of time exists wherein NP of Largemouth bass yields the best impact on growth in the larval stage and later in life when fed SBM-diet. Programming should be performed right after mouth opening using enriched live food and can result in growth similar to non-programmed fish fed FM-based diet. Programming effects similar to that of the live food approach can be achieved with formulated diet, however it is crucial that Largemouth bass are of a proper age and sufficiently developed when programmed with dry food or severe impacts on growth can occur.