Effects of dietary acidification and acid source on fish growth and feed efficiency (Review)

The human population has increased considerably worldwide, including in the Philippines. Aquaculture is one of the main food sectors that provides a cheap source of protein in the Philippines. Changes in diet composition in aquaculture have brought about concerns regarding certain negative effects at the gastrointestinal levels. The replacement of fish meal with a plant protein source in a considerable proportion in the diet of the majority of cultured fish species has led to proliferative and inflammatory responses in the intestines of various (functionally) monogastric animals. In aquaculture feed, the dietary supplementation of organic acids and their salts as growth promoters has been established. The use of acidifiers in aquafeed requires a different approach due to diversified feeding habits and the wide variation in the digestive system structure and physiological function. Dietary organic acids can increase pancreatic enzyme production, decrease stomach pH levels, inhibit pathogens, provide energy, improve mineral utilization and improve nutrient digestibility, all of which improve fish development performance. Acidifiers are currently widely used in animal feed, including aquafeed, and several manufacturers have created next‑generation acidifiers with additional benefits. The present review article discusses the acidifiers, their mechanisms of action, growth, feed efficiency, immunity and future research opportunities. The fish growth rate and feed utilization efficiency are also reviewed as regards dietary acid sources, such as acetic acid, citric acid, hydrochloric acid and control‑no acid. In addition, the attractability of the diets for the fish at different pH levels and dietary acid sources was determined. The survival rates of cultured fishes were determined based on the various dietary acids used. Any acids at an optimum pH level, e.g., pH 4.6 in the diet of tilapia fry, which increase attractability, growth and feed efficiency, warrant further attention.