Feeding Fish for the Future: How Feed Additives Affect Zebrafish Health

The aquaculture industry is rapidly changing, with an average yearly growth rate of 3.7% since 2020. As the aquaculture industry continues to grow, fish are increasingly raised in intensive farming systems to meet global demands. While these systems improve production efficiency, they can also place stress on fish by increasing crowding and disease occurrence. These stressors can slow growth and negatively impact fish health, prompting research to explore ways to improve fish resilience through nutrition.

In this study, Junyu Zhang, working in Dr. David Huyben’s lab at the University of Guelph investigated whether dietary supplements could improve growth, gut health, and survival in farmed fish. This study tested four supplements: black soldier fly (BSF) meal, probiotics, prebiotics, and butyrate, using zebrafish as a model species. A total of 750 juvenile zebrafish were divided into five diet groups, including a control group, and were fed for nine weeks. Zebrafish are commonly used in research because they grow quickly, reproduce easily, and provide valuable insight into how diet affects fish health.

Overall, the study found no statistically significant differences in growth of survival between the different diet groups. However, fish fed the BSF-supplemented diet showed that highest final body weight and the most efficient feed use, meaning they gained more weight per mount of feed consumed. Fish fed the other supplemented diets also tended to weigh more than those fed the control diet. Survival rates were high across all groups, ranging from 77% to 91%, suggesting that none of the supplements had negative effects on fish health.

Researchers also examined gut development, as a healthy intestine plays a key role in digestion, nutrient absorption, and immune function. While difference between groups were not statistically significant, fish fed supplemented diets generally had longer and thicker intestinal villi compared to fish fed the control diet. Butyrate supplementation was associated with longer villi, while BSF meal was linked to thinker intestinal walls, both of which are considered indicators of improved gut health.

In addition, the researchers analyzed the gut bacterial of the zebrafish to determine how diet influences the microbiome. As expected, bacterial diversity decreased as the fish aged and their digestive system matured. Although overall diversity did not differ significantly between diets, each supplement influences which types of bacteria were most abundant. Diets containing BSF meal and probiotics favored beneficial bacteria such as Cetobacterium, while the prebiotic diet resulted in a different bacterial profile dominated by Vibrio. These findings demonstrate that diet can shape the gut microbial community even when overall diversity remains similar.

While most of the results were not statistically significant, the numerical trends suggest that BSF meal and other dietary supplements may benefit fish growth and gut development. The researchers noted that low inclusion level of defatted BSF meal may have limited beneficial effects observed and recommended that future studies explore higher inclusion levels and the addition of insect-derived fats. As research on zebrafish nutrition continues to expand, studies like this help identify more sustainable feeding strategies that could support fish health and productivity in the rapidly growing aquaculture industry.