Effects of dietary yeast inclusion and acute stress on post-prandial whole blood profiles of dorsal aorta-cannulated rainbow trout

Abstract

Yeast is a potential alternative to fish meal in diets for farmed fish, yet replacing more than 50 % of fish meal results in reduced fish growth. In a 4-week experiment, 15 rainbow trout (Oncorhynchus mykiss) were cannulated and fed three diets each week: 30 % fish meal as a control (FM); 60 % replacement of fish meal protein, on a digestible basis, with Saccharomyces cerevisiae (SC); and 60 % replacement with Wickerhamomyces anomalus and S. cerevisiae mix (WA). Blood was collected at 0, 3, 6, 12 and 24 h after feeding. In the final week, fish were exposed to a 1-min netting stressor to evaluate possible diet–stress interactions. Significant increases in pH, TCO2, HCO3 and base excess were found after fish were fed the SC and WA diets compared with FM, which elevated blood alkaline tides. Yeast ingredients had lower buffering capacity and ash content than fish meal, which explained the increase in alkaline tides. In addition, fish fed the WA diet had significantly reduced erythrocyte area and fish fed SC and WA diets had increased mean corpuscular haemoglobin levels, indicating haemolytic anaemia. Higher levels of nucleic acid in yeast-based diets and potentially higher production of reactive oxygen species were suspected of damaging haemoglobin, which require replacement by smaller immature erythrocytes. Acute stress caused the expected rise in cortisol and glucose levels, but no interaction with diet was found. These results show that replacing 60 % of fish meal protein with yeasts can induce haemolytic anaemia in rainbow trout, which may limit yeast inclusion in diets for farmed fish.

Growth performance, nutrient digestibility and intestinal morphology of rainbow trout ( Oncorhynchus mykiss ) fed graded levels of the yeasts Saccharomyces cerevisiae and Wickerhamomyces anomalus

“…The tip of the villi are normally hypoxic, but the hypoxic area can extend further down in the villi during neutrophil infiltration and/or decreased blood perfusion of the intestine (Colgan & Taylor, ). Huyben et al () who fed rainbow trout the same diets as in the present study found that fish fed the yeast‐based diets displayed signs of haemolytic anaemia. Those authors suggested that high levels of nucleic acids in yeast‐based diets could overwhelm anti‐oxidative processes and impair red blood cells, consequently leading to cell lysis, and recommended limited use of yeasts in fish diets.…”

Dietary live yeast and increased water temperature influence the gut microbiota of rainbow trout

“…; Huyben et al . ), although the highest gut pH was found in fish fed FM in cold water (i.e. 8·51) and suggests that the buffering capacity of FM was impaired at lower temperatures while yeast was unaffected.…”

“…6). Previous studies have found that FM has a higher buffering capacity than yeast (Montanez-Valdez et al 2013;Huyben et al 2017b), although the highest gut pH was found in fish fed FM in cold water (i.e. 8Á51) and suggests that the buffering capacity of FM was impaired at lower temperatures while yeast was unaffected.…”

Effects of dietary yeast inclusion and acute stress on postprandial plasma free amino acid profiles of dorsal aorta-cannulated rainbow trout

“…This study was part of a larger study that investigated whole blood and cortisol parameters after feeding fish meal‐ and yeast‐based diets to rainbow trout and contains more information on tank design, DA cannulation and blood sampling methods, see Huyben et al. ().…”

“…The study was performed in compliance with laws and regulations on the use of animals for research purposes in Sweden, which is overseen by the Swedish Board of Agriculture (permit reference C74-14). This study was part of a larger study that investigated whole blood and cortisol parameters after feeding fish meal-and yeast-based diets to rainbow trout and contains more information on tank design, DA cannulation and blood sampling methods, see Huyben et al (2016).…”