The Effect of Corn Starch and Kappa-Carrageenan Probiotic Encapsulation on Growth and Immune Response in Chinook Salmon (Oncorhynchus tshawytscha)

Abstract

As vaccines have limited efficacy in fish, alternative preventative measures are used to combat infectious diseases in aquaculture, including probiotics. To be effective, a probiotic must remain stable during storage, feeding, and transit through the gastrointestinal tract. Thus, preparing probiotic feed requires the use of a coating agent and several different types have been tested, as some have adverse effects. To better understand the effect of corn starch and kappa () -carrageenan as a combined coating agent on growth and immune performance in Chinook salmon, a growth trial was conducted. Three different treatments were used, including regular feed, regular feed with a corn starch and -carrageenan coating, and probiotic feed with the same coating. The probiotic feed included a mixture of BioPower® PA (Pediococcus acidilactici, strain CNCM MA 18/5M; Lallemand Inc., Canada) and Seed 14 (Limosilactobacillus reuteri LRE2; Probiotical SpA, Italy). Sampling timepoints were at 0-, 1-, 3-, 7-, and 28-days post diet-introduction, and at each sampling timepoint, the weight and length of 6 fish per treatment were measured, and the head kidney, spleen, and hindgut were collected. There was an additional timepoint at Day 42 where the weight and length of the remaining fish in each barrel were recorded, but no tissues were collected. To assess immunological effects of the coating agent, qPCR for IL-1, IL-8, and TGF- was performed on spleen, head kidney, and hindgut samples. In the hindgut, additional genes were assessed to determine changes in gut barrier integrity, including E-cadherin, claudin 15, junctional adhesion molecule 1 alpha, mucin 2, tricellulin, villin 1, and zonula occludens-1. No significant differences in weight or length were observed between treatments measured over 42 days. No significant differences were found in the assessed proinflammatory transcript levels in the spleen or head kidney sampled at 0-, 1-, 3-, 7-, and 28-days post diet-introduction. Transient changes in the regulatory cytokine TGF- were seen in these tissues. In the hindgut, upregulation of all three immune transcripts were seen on Day 7 in both coated treatments, but these changes were transient, with no significant differences seen on Day 28. Transient changes were also seen in gut barrier gene expression, with no significant differences seen between treatments on Day 28. These results suggest that corn starch and -carrageenan as a combined coating agent has no short-term negative effects on the growth or immune status of Chinook salmon and that it can be used to deliver probiotics that will improve the health of fish in aquaculture.