Abstract
The growth rate of farmed fish is an important factor regarding aquaculture success. An understanding of the cellular events that occur in skeletal muscle when fish undergo periods of fasting and refeeding provides information useful in developing alternative feeding strategies for improving muscle growth in commercially cultivated species. To evaluate the effect of 1–3 weeks of fasting and 10 weeks of refeeding in Nile tilapia juveniles, we analyzed the growth performance and changes in muscle cellularity and the expression of the following growth and muscle related genes: MyoD, myogenin, IGF-1, IGF-1 receptor, MuRF-1, atrogin-1 and myostatin. Reduced body mass was observed in all three groups of fasted fish during their time off feed, and 10 weeks of refeeding resulted in partial compensatory growth of body mass. No differences in the frequency of white muscle fiber diameters were observed between fasted and fed control fish treatments. However, changes in gene expression induced by fasting and refeeding were found. IGF-1 receptor, ubiquitin ligases MuRF1 and atrogin-1 expression increased during the 1–3 weeks of fasting, while IGF-1 levels dropped significantly (P < 0.001) compared to the control treatment. Furthermore, myogenin mRNA level in fish submitted to 3 weeks of fasting was higher in comparison to the control treatment (P < 0.05). Overall, our results showed that 1–3 weeks of fasting can induce muscle atrophy activation in Nile tilapia juveniles, and 10 weeks of refeeding is enough to induce only partial compensatory growth.
Highlights
Fasting is a phenomenon that can occur naturally in the environment due to low food supply, during fish migration, overwintering or during reproduction, throughout which fish demonstrate the ability to survive without food for lengthy periods (Love 1970; Bower et al 2009)
We investigated if fasting for a certain interval followed by 10 weeks of refeeding would change muscle gene expression
We wanted to evaluate if this starve/refeed regime would cause alterations in white muscle fiber plasticity and morphology in Nile tilapia Oreochromis niloticus juveniles
Summary
Fasting is a phenomenon that can occur naturally in the environment due to low food supply, during fish migration, overwintering or during reproduction, throughout which fish demonstrate the ability to survive without food for lengthy periods (Love 1970; Bower et al 2009). After a period of growth depression and when favorable conditions are restored, there occurs a phase of accelerated growth, called compensatory growth (Ali et al 2003). Full and over-compensation growth have all been evoked in fish. Compensatory growth has been partially linked to hyperphagia when rates of food consumption are significantly higher than those in fish that have not experienced a previous growth depression episode. The severity of the growth depression increases the duration of the hyperphagic phase rather than maximum daily feeding rate. A significant amount of research effort has been expended in understanding the regulatory factors surrounding muscle accretion, evaluation of the genes involved. Myogenic regulatory factors (MRFs) are a family of four transcription factors (MyoD, myogenin, myf and MRF4/myf6) that are highly conserved in vertebrates and are responsible for the control of myogenesis and muscle growth. MyoD and myf are essential regulators of muscle cell proliferation determination, whereas myogenin and myf act as regulators of muscle cell differentiation (Rudnicki et al 1993; Steinbacher et al 2007; Johnston et al 2008)
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