The value of the zebrafish in biomedical research is not questioned. However, knowledge of the specific nutritional requirements of zebrafish is limited. Open formulation diets are being designed to optimize growth and health profiles, including reproductive outcomes. This has resulted in the formulation of a proposed standard reference diet (SRD) designed to support clinically healthy fish. Currently, the protein sources for this diet are casein and fish protein hydrolysate (FPH), a fish meal derivative. Both are high value protein sources; however, FPH is produced from wild-caught fish, so its nutritional composition and level of environmental toxicants may be variable. Other protein sources may improve the nutrient profiles required in an SRD. Recent successes with a bacterial-based source of protein suggest the value of bacteria as a protein source. A reference protein source that is stable in amino acid composition and promotes health will further support the use of zebrafish as a high throughput translational model.
Bacterial protein sources can be produced using agricultural waste products and can be genetically modified to adjust amino acid composition. We evaluated the physiological impact of a commercially-produced, bacterial-based single cell protein (MRD-Pro, Meridian Biotech) when used as a replacement for FPH and CAS. Zebrafish were fed Brachionus and Artemia nauplii until 35 days post fertilization, then were fed ad libitum one of seven experimental diets. The protein content of the diets were as follows: proposed SRD (FPH and CAS as protein), MRD 2019 formulation and CAS, MRD 2024 formulation and CAS, autoclaved MRD 2024 and CAS, MRD 2024 alone, FPH alone, and CAS alone. Zebrafish were housed in recirculating aquatic systems, and the weights and lengths of the zebrafish were tracked every two weeks for 16 weeks. The SRD outperformed all other diets in weight gain, and the diets with only SCP as a protein source underperformed. Diets with SCP included with FPH performed adequately. Further analysis of body composition, gene expression, plasma lipid circulation, and microbiome are underway. Funded by NIH STTR.