Haematological and intestinal health parameters of rainbow trout are influenced by dietary live yeast and increased water temperature

Abstract

Live yeast may be a sustainable protein source in salmonid diets while exhibiting a probiotic effect to counteract environmental stressors, such as increased water temperature that is being exacerbated by climate change. The objective of this study was to evaluate the effects of feeding a high dietary inclusion of live yeast and increased water temperature on growth, haematological and intestinal physiology of rainbow trout. For six weeks, 129 g fish in 16 tanks (n=4) were fed either a diet based on fishmeal or based on live yeast (214 g kg -1 of diet or 7.6 log CFU g -1 of Saccharomyces cerevisiae) that replaced 40% of fishmeal protein while fish were reared in water temperatures of either 11 °C (cold) or 18 °C (warm). Fish weights, caudal blood and proximal and distal intestines were collected and analysed. Fish fed live yeast resulted in reduced growth (SGR and WG) and higher FCR, while growth in cold and warm water was similar despite differences in TGC. However, increased mortality, plasma cortisol, and intestinal oedema and villous damage indicated fish reared in warm water were subjected to chronic stress. Temperature had a significant effect on haematocrit and red blood cell counts that resulted in significantly higher haemoglobin levels in fish kept in warm water attributed to an elevated oxygen demand. In the proximal intestine, increased temperature resulted in reduced expression of pro-inflammatory cytokines, e.g. TNFα and IL8, that were further reduced in fish fed live yeast. In addition, feeding live yeast reduced gene expression of CLD6 involved in gut barrier function, which suggests that the level of yeast was too high and masked any beneficial effects on fish health. In conclusion, feeding a high inclusion of live yeast reduced fish growth and expression of intestinal genes, while increasing the temperature from 11 to 18 °C subjected fish to chronic stress that restricted growth, suppressed innate immunity and induced intestinal damage. Replacing 40% of fishmeal protein with live yeast did not counteract negative effects caused by increased temperature, thus alternative strategies need to be explored and implemented to protect the growth and health of rainbow trout from seasonal and long-term rises in water temperature.

Association of Gut Microbiota With Metabolism in Rainbow Trout Under Acute Heat Stress

“…The rainbow trout ( Oncorhynchus mykiss ) is an artificially cultivated cold-water fish that is very sensitive to changes in water temperature. When the water temperature exceeds 18°C, the rainbow trout (adult fish) has a stress response, which may lead to reduced food intake, abnormal behavior, growth inhibition, and even death ( Wendelaar, 1997 ; Huyben et al, 2019 ; Zhou et al, 2019 ). The gut is particularly sensitive to any type of stress, including heat stress ( Sundh et al, 2010 ).…”

Multi-Approach Assessment for Stress Evaluation in Rainbow Trout Females, Oncorhynchus mykiss (Walbaum, 1792) from Three Different Farms during the Summer Season

“…As other studies demonstrated, many biotic and abiotic factors can affect blood parameters in fish [ 22 , 38 , 39 ]. Seasonal differences in blood biomarkers may occur due to alterations in water physicochemical parameters, such as differences in temperature, dissolved oxygen concentration, rainfall, river deposits, decomposing organic matter, dissolved solids, etc.…”

“…Seasonal differences in blood biomarkers may occur due to alterations in water physicochemical parameters, such as differences in temperature, dissolved oxygen concentration, rainfall, river deposits, decomposing organic matter, dissolved solids, etc. During summer, stress due to improper water temperatures and low dissolved oxygen levels is an increasingly common issue, severely affecting the growth performances of rainbow trout [ 6 , 22 ]. The data obtained in our study regarding the physicochemical parameters of the water in the three farms are in accordance with other studies [ 40 , 41 , 42 , 43 , 44 ], which follow the environmental parameters necessary for the normal development of rainbow trout.…”

“…Steroid hormones are involved in the regulation and progress of some physiological processes in vertebrates, such as embryonic development, sex differentiation, metabolism, immunological responses [ 13 , 22 ], circadian rhythms, stress responses, and reproduction [ 23 ]. The hypothalamus–pituitary–interrenal and the hypothalamus–pituitary–gonadal axes control steroid biosynthesis in teleost fishes, which usually occurs in peripheral tissues, such as the gonads, interrenal gland, and brain [ 23 , 24 ].…”

Stress management in aquaculture: a review of dietary interventions

“…On the contrary, Huyben et al . (2019) documented that the inclusion of live yeast, Saccharomyces cerevisiae (by replacing 40% of fishmeal protein) in rainbow trout feed did not counteract the adverse effects of high‐temperature stress. Several researchers opinioned that the richness of nucleotides, β‐glucans, mannan oligosaccharides, and chitin makes yeast a potential immunomodulator and stress mitigator (Gong et al .…”