# Feeding for Well-Being: Porcine Blood Hydrolysate Supplementation Improves Metabolic and Welfare-Related Traits in Farmed Gilthead Sea Bream (Sparus aurata)

## TL;DR

Adding porcine blood hydrolysate to fish feed improves metabolism and welfare in gilthead sea bream.

## Contribution

This study shows PBSH as a novel functional feed ingredient with benefits for fish health and performance.

## Key findings

- PBSH reduced liver fat and stress indicators like cortisol and glucose in fish.
- Fish fed PBSH showed improved swimming performance and faster weight recovery after fasting.
- PBSH altered gut bacteria, increasing genera like Aureimonas and Halomonas.

## Abstract

The revalorization of animal by-products, such as porcine blood, is a key strategy for sustainable aquaculture and circular economy practices. This study aimed to fill the existing knowledge gap on the effects of spray-dried porcine blood hydrolysate (PBSH), assessing its potential as a functional feed ingredient for gilthead sea bream. Two practical diets were formulated: a control diet containing 5% blood meal, and a PBSH diet including 5% PBSH previously characterized in vitro. The results indicated that the PBSH diet promoted lower hepatosomatic index, a down-regulation of key hepatic lipogenic enzymes (scd1b, hl, lpl), and a better stress condition with lower circulating levels of glucose and cortisol and a reduction in aggressive attacks. Positive findings were also achieved in energy management, obtaining lower metabolic rates along with an enhanced swimming performance (20% increase in the critical speed) and a quicker weigh recovery after a fasting period. The PBSH diet also shaped the intestinal bacterial composition, determining a redistribution of abundant genera including Aureimonas and Halomonas. Ultimately, this study demonstrated that PBSH would act as a functional ingredient capable of enhancing fish energy management and resilience in the face of stressful events, exhibiting a transient transcriptional modulation, yet persistent physiological and welfare benefits.