The objective of the study was to evaluate the impact of different concentrations of dietary red beet and betaine on the growth performance and fish flesh quality of rainbow trout. Therefore, a control diet was compared with four diets in which two levels of red beet (14% and 28%) and betaine (0.9% and 1.63%) were incorporated in combination. The study was set up with an average body weight of 69 ± 2.2 g and finished when fish reached commercial weight (175-250 g) after 105 d. The impact of the diets was studied based on the growth performance, biometric indexes, proximal composition, protein and fat retention efficiencies and apparent nutrient digestibility by fish reared on a recirculation system. Further estimates were the effect of red beet and betaine on the flesh proximate composition and quality of the final product (water activity, colour, texture, thiobarbituric acid reactive substances and sensory characteristics). Results showed that inclusion of 14% red beet and 0.9% betaine did not affect growth, nutritive or biometric parameters and nutrient retention when compared with the control diet. However, higher levels of red beet and betaine had negative effects on growth and nutritive parameters. The tested ingredients enhanced quality parameters regardless of the concentration used. After feeding the red beet and betaine, fish flesh showed lower water activity and better textural and colour properties than the control and also a dose-dependent effect on lipid oxidation was observed.
Barley concentrations ranging from 0% to 32% (0B, 40B, 80B, 160B and 319B) were incorporated into rainbow trout, Oncorhynchus mykiss (Walbaum) diets. The experiment started with an initial average fish weight of 127.72 ± 5.65 g and finished when they reached commercial weight (final weight between 312-330 g) after 84 days. The inclusion of barley in the diets did not show a significant effect on growth and biometric parameters, fat and carbohydrate digestibilities, however, protein digestibility decreased significantly with the incorporation of barley on diets. Glucose levels increased significantly with barley concentration in the diet and lactate and cortisol levels were also significantly affected after a stress period regardless of the diet. Meat quality was influenced as well by barley concentration. Lower water activity values and an enhancement in textural and colour properties, were observed in fish fed with the diet containing the highest barley concentration. Trout fed feed with higher concentrations of barley (160B) showed lower lipid oxidation levels than those fed with lower concentrations (control and 40B). The sensory panel found that fish fed with diets higher than 8% in barley content (80B), exhibited a brighter red colour in gills and a better texture, also meat colour became redder with a higher barley inclusion (160B and 319B), being all these sensory parameters correlated with fish freshness. Thus, results indicate that barley can be substituted for wheat fraction without any detrimental effect on production efficiency and enhancing fish quality.
This study evaluates the effects of red beet (RB) and betaine on rainbow trout submitted to an acute stress challenge. A control diet was compared with four experimental diets in which red beet (14 and 28%) and betaine (0.9 and 1.63%) were incorporated in different concentrations according to a factorial design. Cortisol in plasma and fin, glucose and lactate plasma levels, and malondialdehide (MDA) in muscle were all measured before the stress challenge and 30 min and 6 and 12 h after the stress challenge as parameters to determine the diet effects. RB and betaine had no effect on cortisol, glucose, and MDA basal levels. However, lactate basal levels were significantly lower on fish fed with RB and betaine. Thirty minutes after the stress challenge, there was a significant increase in plasma and fin cortisol, glucose and lactate concentrations, although fish fed with diets containing RB and betaine showed significantly higher plasma cortisol values. MDA values of fish fed with 14% RB and 0.9% betaine were significantly higher than MDA values from fish fed with 28% RB and 1.63% betaine. After 6 and 12 h, plasma and fin cortisol and lactate levels recovered in a similar trend. Glucose plasma levels recovered in almost all groups 12 h after the stress. Also, MDA values recovered basal levels after 6 and 12 h. RB and betaine did not enhance the tolerance to the stress challenge compared to the control group, although the presence of these ingredients had no negative effect on any of the stress indicators.
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