Different dietary combinations of high/low starch and fat with or without bile acid supplementation on growth, liver histopathology, gene expression and fatty acid composition of largemouth bass, Micropterus salmoides

Authors: ROMANO, NICHOLAS - University Of Arkansas At Pine Bluff; FISCHER, HAYDEN - University Of Arkansas At Pine Bluff; RUBIO-BENITO, MARINA - University Of Idaho; Overturf, Kenneth - Ken; SINHA, AMIT KUMAR - University Of Arkansas At Pine Bluff; KUMAR, VIKAS - University Of Idaho

Submitted to: Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2022
Publication Date: 1/31/2022
Citation: Romano, N., Fischer, H., Rubio-Benito, M., Overturf, K.E., Sinha, A., Kumar, V. 2022. Different dietary combinations of high/low starch and fat with or without bile acid supplementation on growth, liver histopathology, gene expression and fatty acid composition of largemouth bass, Micropterus salmoides. Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology. 266. Article 111157. https://doi.org/10.1016/j.cbpa.2022.111157.
DOI: https://doi.org/10.1016/j.cbpa.2022.111157

Interpretive Summary: The use of fishmeal as a protein source in aquaculture diets is continually being reduced due to its limited availability and high cost. Largemouth bass (LMB) are native to North America but are a high value aquaculture product that is now being farmed internationally. LMB require high levels of protein in their diet which can make their feed quite expensive. Starches are a less expensive option to satisfy that could be used to spare protein and satisfy dietary energy requirements for LMB. However, high levels of starch have been show to adversely affect LMB by reducing growth rates and survival, and causing oxidative stress and liver damage. However previous studies have shown that bile salts may mitigate these adverse effects. Therefore an experiment was set up evaluating eight diets that varied in fat and starch levels and with and without the addition of bile acids. Overall effects showed that in some case the use of bile salts could increase growth for some diets and reduce liver damage. But even with the inclusion of bile salts it was found that the fish reared on low fat/low starch diets had overall better growth and liver health.

Technical Abstract: High dietary levels of fat and starch can reduce growth and cause extensive liver inflammation that is linked to mortalities in largemouth bass (LMB), Micropterus salmoides. However, bile acids (BA) may mitigate these adverse effects. In a 2 × 2 × 2 factorial feeding trial, M. salmoides juveniles were fed different combinations of dietary high (HF) and low fat (LF) and high (HS) and low starch (LS) levels with or without bile acid (BA) supplementations at 1% for 8 weeks. A total of 8 isonitrogenous diets were formulated to include, HF/LS, HF/HS, LF/HS, LF/LS, HF/LS-BA, HF/HS-BA, LF/HS-BA and LF/LS-BA. Survival, growth performance, feeding efficiency, whole-body proximate composition, muscle/liver fatty acid composition, hepatic expression of growth regulator (GH/IGF1 axis), lipid metabolism (fatty acid synthase ‘FASN’ and cholesterol 7 alpha-hydroxylase ‘CYP7A1’) and antioxidant capacity (superoxide dismutase ‘SOD’) genes as well as liver histopathology were assessed. Results showed that among diets without BA, there was no significant effect on growth or feeding efficiency, but when BA was included this led to more variable effects including significantly higher weight gain in the LF/HS-BA group compared to all others fed BA. The HF, HS or their combination led to extensive hepatic inflammation, but BA appeared to mitigate this in the LF/HS group (i.e. LF/HS-BA). No abnormal liver histopathology was observed in the LF/LS and LF/LS-BA treatments. Muscle 22:6n-3 was significantly higher in the HF/LS and HF/HS-BA groups compared to those fed the HF/HS or LF/LS diets. Dietary fat had a significant effect on the moisture, crude lipid, and caloric content of M. salmoides. Hepatic expression of IGF-I and CYP7A1 were differentialy modulated under different treatments. Overall, these results show that BA can mitigate liver inflammation caused by high dietary starch; however the LF/LS diets led to a better balance between growth performance and liver health.