Amelioration of growth performance, physio-metabolic responses, and antioxidant defense system in rainbow trout, Oncorhynchus mykiss, using dietary dandelion, Taraxacum officinale, flower extract

Highlights

• Administration of dandelion flower (DF) extract can be considered as a growth promoter in rainbow trout.

• Feeding the fish with DF extract at 3 g/kg increased the hematological parameters and digestive enzyme activity.

• Dietary DF extract at 3 g/kg up-regulated the transcriptomic responses of growth genes and down-regulated antioxidant genes.

• Adding DF extract at 2.59 to 3.13 g/kg in rainbow trout diet is recommended based on the polynomial regression models.

Abstract

In our study, the dietary effect of dandelion flower (DF) extract on growth performance, hemto-biochemical parameters, and transcriptomic responses of growth and antioxidant genes in rainbow trout were investigated. Accordingly, three hundred fingerlings were randomly stocked into 15 tanks and fed with different levels of DF extract (0 [control], 1, 2, 3, and 4 g/kg) for 8 weeks. The results showed the weight gain was significantly increased in 3 g/kg DF extract-supplemented group. The feed conversion ratio was significantly decreased in 3 and 4 g/kg DF extract treatments compared to the control group. The highest number of red blood cells and hematocrit level were observed in 3 g/kg DF extract treatment compared to 1 g/kg DF extract and the control group. A significant rise in the serum high-density lipoprotein, glutathione peroxidase (GPx), and catalase (CAT) was obtained in 3 g/kg DF extract. However, the levels of serum alanine and aspartate amino transaminase, and glucose were remarkably decreased at 3 g/kg DF added-group. The intestinal protease activity was significantly enhanced in the fish fed 3 g/kg DF extract compared to others. The body crude protein was also remarkably increased in the fish fed 3 g/kg DF extract. The transcriptomic responses of growth hormone, insulin-like growth factor-1, and ghrelin genes were notably up-regulated in the treated fish, especially in 3 g/kg DF extract. However, the expression of antioxidant-related genes (SOD, CAT, and GPx) was significantly decreased in DF extract-added groups. Overall, the optimal inclusion of DF extract in rainbow trout diet was ranged from 2.83 to 3.13 g/kg and 2.59 to 2.75 g/kg to improve growth performance and antioxidant status, respectively.

Introduction

Aquaculture is undoubtedly the fastest-growing animal protein production around the world as we encounter a population of 9.7 billion in 2050. However, the intensification of aquaculture has led to increasingly stressful conditions for the cultured aquatic animals which can reduce the growth rate and ultimately cause remarkable economic losses (Paknejad et al., 2020; Srichaiyo et al., 2020). Chemotherapy routes are one of the common ways to overcome this problem, while the main purpose of recently published documents is focusing on natural compounds as a feed additive in aquaculture nutrition to improve the growth rate, appetite, digestive system, and hemato-biochemical parameters (Mohammadi et al., 2020; Zemheri-Navruz et al., 2020).

Poor management strategies in intensive and semi-intensive aquaculture operations can suppress the growth performance (Hanke et al., 2020) and antioxidant system of the cultured aquatic (Pérez et al., 2020). However, the antioxidant defense system is a vital physiological function to maintain homeostasis in fish (Huang et al., 2021). In this vein, phytomedicines due to their active biomolecules (e.g. alkaloids, terpenoids, saponins, pigments, and flavonoid components) considerably have been utilized in aquaculture to stimulate growth performance and render antioxidant activity (Chakraborty et al., 2014). Dandelion (Taraxacum officinale L.) is a valuable plant in herbalism and exhibits a wide range of pharmacological effects such as anticarcinogenic (Sigstedt et al., 2008), anti-altherosclerotic (Lis and Olas, 2019), antirheumatic (Hu and Kitts, 2005), and anti-oxidative properties (Ivanov, 2014; Jędrejek et al., 2017; Lis and Olas, 2019). Dandelion flower (DF) components represent a wide range of bioactive compounds (e.g. polyphenols, chlorogenic acid, phenols, and luteolin) with free radical scavenging properties and inhibitory effects on the formation of hydroxyl radicals by intracellular oxidation (Majewski et al., 2021). Moreover, DF is rich in fatty acids, minerals, vitamins, and antimicrobial components (Astafieva et al., 2012; Amin Mir et al., 2016) which can be used as a potential feed additive to improve the growth traits, hematological profiles, and health status of cultured fish species by the administration of DF-enriched diets. In this vein, the beneficial dietary effects of dandelion hydro-ethanoic extract on the growth performance, physiological responses, and antioxidant status were reported in golden pompano (Trachinotus ovatus) (Tan et al., 2017b; Tan et al., 2018c) and hybrid grouper (Epinephelus lanceolatus♂ × Epinephelus fuscoguttatus♀) (Sun et al., 2019). Moreover, in our recent study, immune responses and disease resistance against Streptococcus iniae infection in rainbow trout were notably improved by dietary levels of DF extract (Unpublished data). However, to the best of our knowledge, no information is available about the dietary effect of DF on growth, hematological, and antioxidant activities in rainbow trout (Oncorhynchus mykiss) as one of the most cultured and commercial fish species in cold-water aquaculture sectors around the world due to high adaptation ability to captivity conditions, fast-growing, and easy to spawn.

According to the economic importance of rainbow trout in the global aquaculture industry and the innumerable benefits of DF as a feed additive, the current study was performed for the first time to evaluate the dietary effect of DF extract on growth performance and feed utilization, some hematological and serum biochemical profiles, antioxidant capacity, and mRNA transcription levels of growth and antioxidant-related genes in rainbow trout.