# Feasibility of Rainbow Trout (Oncorhynchus mykiss) Fry Rearing in Biofloc System: Effect of Total Suspended Solid Levels on Zootechnical Performance, Intestinal Condition and Antioxidant Enzyme Activity

## TL;DR

This study shows that rearing rainbow trout fry in a biofloc system with moderate suspended solids is feasible and beneficial for growth and health.

## Contribution

The study demonstrates that biofloc systems can be successfully used for rainbow trout fry with optimal suspended solid levels.

## Key findings

- Biofloc systems with 250 mg L−1 suspended solids maintained good growth and health in rainbow trout fry.
- Higher suspended solids (350 mg L−1) reduced growth but increased probiotic bacteria in the gut.
- Biofloc systems offer improved biosecurity and water efficiency for trout fry rearing.

## Abstract

This study evaluated the effects of different biofloc total suspended solid (SST) levels (0, 250 and 350 mg L−1) on the productive performance, intestinal condition and antioxidant enzyme activity of rainbow trout (Oncorhynchus mykiss) fry reared in a biofloc technology (BFT) system. Rearing rainbow trout fry in a BFT system with TSS levels up to 250 mg L−1 proved feasible, maintaining zootechnical performance, intestinal condition and antioxidant enzyme activity during the early stages of development. In contrast, the TSS concentration of 350 mg L−1 negatively affected fry growth performance. Despite this, increased gut colonization by lactic acid bacteria was observed, indicating that biofloc may serve as a source of probiotic bacteria for rainbow trout. The BFT system is recommended as an alternative system for rearing rainbow trout fry, offering enhanced biosecurity and reduced water consumption.

This study evaluated the effects of different total suspended solid (SST) levels (0, 250 and 350 mg L−1) on the productive performance, intestinal condition and antioxidant enzyme activity of rainbow trout (Oncorhynchus mykiss) fry reared in a biofloc technology (BFT) system. The experimental design was completely randomized with three treatments and five replicates. A total of 225 rainbow trout fry (0.81 ± 0.06 g) were distributed into 15 tanks (70 L working volume) at a stocking density of 15 fish per tank. Tanks designated for the control treatment (clear water) were connected to a recirculating aquaculture system, whereas BFT treatments were maintained in independent units. Performance analyses were conducted and fish were sampled for intestinal histomorphometry, intestinal microbial counting and antioxidant enzymatic activity. Rearing rainbow trout fry in BFT systems with TSS levels up to 250 mg L−1 proved feasible and preserved zootechnical performance, intestinal condition and antioxidant enzyme activity during the early stages of development. The higher TSS concentration negatively affected fish growth performance. However, increased colonization by lactic acid bacteria was observed, indicating that biofloc may serve as a source of probiotic bacteria. The BFT system is a viable alternative for rearing rainbow trout fry, enhancing biosecurity and reducing water consumption.