The declining availability and rising costs of fishmeal are driving the aquafeed industry to seek alternative high-quality protein sources. In a recent study, researchers evaluated chicken hydrolysates as potential substitutes for fishmeal in diets for Pacific white shrimp.
Pacific white shrimp (Litopenaeus vannamei) are among the most economically important aquaculture species globally, but reduced fishmeal supply and the increasing prices caused by El Niño events, unfavourable marine conditions, and overfishing threaten the sustainability of white shrimp production.
Chicken hydrolysates and circularity
In a study published in the Aquaculture Reports journal, researchers elaborate on how chicken soluble hydrolysates are potential replacements for fishmeal in the diets of white shrimp. Chicken soluble hydrolysate (CSH) is produced through the enzymatic hydrolysis of poultry by-products, such as chicken frames, intestines, feet, and blood, excluding feathers. Protein sources treated by enzymatic digestion not only expand the processing and utilisation of poultry by-products but also provide a way to develop new protein sources for aquafeed. Compared with intact proteins, hydrolysates consist of small-molecular-weight peptides that are more readily absorbed by intestinal cells and thus more readily assimilated.
Previous studies on common carp and largemouth bass have also found that chicken hydrolysates improve gut health and the abundance of gut microorganisms without adversely affecting growth performance.
Replacing fishmeal with chicken soluble hydrolysates
This study evaluated the use of chicken soluble hydrolysates (with varying compositions) as substitutes for fishmeal in the diet of white shrimp (L. vannamei) and assessed their effects on growth performance, immunity, and intestinal and hepatopancreatic health. Based on the control group (fishmeal, FM) feed, fishmeal was replaced by 5% by mass with the addition of 5% chicken soluble hydrolysate 1 (CSH1), 2 (CSH2), 3 (CSH3) and 4 (CSH4), to prepare 5 experimental feeds that are isonitrogenous and isolipidic, as shown in Table 1.
Impact on growth performance
Across all measured indicators, shrimp fed chicken soluble hydrolysate (CSH) diets grew better than those fed the fishmeal (FM) control (Table 2). Among the hydrolysates, hydrolysate-2 (CSH2) consistently showed the most balanced and superior combination of high growth and efficient feed use; the FCR was lowest or most improved in the CSH2 and CSH3 diets. The weight gain rate was higher in all the CSH groups compared to the fishmeal group. Both the Protein Efficiency Ratio and Lipid Efficiency Ratio were higher in the 3 CSH groups (CSH1, CSH2 and CSH3), compared to the FM and CSH4-fed shrimp.
CSH2 had a moderate crude protein content (33.01%), indicating a moderate degree of enzymatic hydrolysis; the researchers noted that moderate hydrolysis improves growth, whereas excessively high or low levels reduce performance. On the other hand, higher enzyme activity enables shrimp to digest and absorb nutrients more efficiently, thereby supporting faster growth. In addition, CSH2 produced the strongest stimulation of intestinal digestive enzymes (α-amylase, trypsin and lipase) (Table 2).
Improving intestinal functions
The researchers observed that villus height was highest in the CSH2 group, whereas intestinal villus width did not differ significantly among the CSH groups and the FM group. The intestinal muscle layer thickness in the CSH groups was significantly higher than in the FM group. These intestinal histology features of the CSH2 group are associated with an increase in nutrient absorption surface area and improved gut motility, which was in line with the observed enhanced growth performance in the CSH2 group.
Antioxidant enzyme activity boost
Research shows that a better antioxidant status reduces metabolic stress, allowing more energy to be directed to growth. Antioxidant enzymes have protective and ameliorative effects on shrimp health. A lack of antioxidant enzymes in the body can lead to metabolic disorders and even death in severe cases. For example, phenoloxidase (PO) oxidises phenolic substances, inducing the production of melanin and intermediates that can kill microorganisms and parasites that invade the shrimp’s body.
The CSH groups increased the activity of antioxidant enzymes phenoloxidase (PO), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX), while lowering malondialdehyde (MDA), the indicator of oxidative stress.
Improving hepatopancreatic health
On the other hand, a healthier hepatopancreas improves digestion, metabolism and overall growth efficiency. Among the groups, the CSH2 group showed the lowest serum alanine aminotransferase (ALT) and aspartate transaminase (AST) (indicating less stress and better organ function), and larger, healthier nutrient-absorbing Restzellen cells (R cells). R cells are among the principal cell types in the hepatopancreas of shrimp and other crustaceans. R cells are indicators of hepatopancreatic health and metabolic capacity as they are involved in nutrient absorption and storage.
Upregulated immune gene expression
Better immunity reduces subclinical infections and inflammation, allowing more energy for growth. In this study, the CSH2 diet strongly upregulated key immune genes (lyz, akp, acp, alf, cru and pen3) compared to the other diets. The researchers suggested that this indicates greater disease resistance and improved physiological resilience in shrimp fed the CSH2 diet.
The researchers concluded that chicken soluble hydrolysates are potential sustainable alternatives to fishmeal in the diets of Pacific white shrimp, as evidenced by improvements in growth performance, immunity, antioxidant status, and intestinal and hepatopancreatic health.
They emphasised that the efficacy of hydrolysates mainly depends on the following:
- optimal nutrient composition
- the degree of hydrolysis
- the inclusion level or replacement level in the fishmeal-based diets.
