Abstract
The effects of Tenebrio molitor larvae meal (TM) dietary inclusion in rainbow trout diet were evaluated on muscular growth using gene expression and histomorphological features of liver, spleen, kidney, anterior and posterior gut through histopathological analyses. Two hundred fifty-two grow-out rainbow trout were fed four experimental diets containing increasing levels of TM: 0% (TM0), 5% (TM25), 10% (TM50), and 20% (TM100) corresponding to different levels of fish meal replacement (0, 25, 50, and 100%, respectively). Muscular growth was evaluated analysing the expression of various genes involved in different steps of myogenesis. Among the analysed genes, only MyoD expression resulted significantly higher in fish fed TM100 compared to fish fed TM0. The gut histomorphology was not affected by TM dietary inclusion and villus height differs from anterior and posterior segments regardless of the fed diet. Histopathological alterations were observed in all the sampled organs for all the dietary treatments; however, dietary TM inclusion did not influence either development or severity of the observed histopathological changes. The results obtained confirmed the safe utilisation of TM as an alternative protein source in rainbow trout diets and highlighted the necessity to deepen the studies of TM effect on the myogenesis process, especially at a molecular level. Highlights Rainbow trout can effectively be fed with a TM protein source. Total FM substitution by TM (TM100) decreased MyoD gene expression. Increasing TM dietary inclusion did not influence gut histomorphology.
Highlights
In recent years, a growing interest in insect meal as an alternative protein source in aquafeed has promoted investigations and related scientific production
Results showed that total fish meal (FM) replacement with Tenebrio molitor larvae meal (TM) (TM100) affected myoblast determination protein (MyoD) RNA level, which was significantly (p < .05) higher in TM100 samples compared to the TM: 0% (TM0) control diet (Figure 1)
Quiescent satellite cells display no detectable levels of myogenic regulatory factors (MRFs) expression, whereas, upon satellite cell activation, MyoD expression is rapidly up-regulated before other MRFs involved in the myogenesis process (Sabourin and Rudnicki 2000)
Summary
A growing interest in insect meal as an alternative protein source in aquafeed has promoted investigations and related scientific production. The assessment of animal health status represents a crucial aspect when a novel feed ingredient is tested for its introduction in commercial fish farming. Optimal growth performance is one of the features that reflects fish health and still represents a crucial aspect for the farmers. Up to 90% of these muscles mainly consist of deep fast white fibres covered by a thin superficial layer of slow red muscle fibres are located under the skin, with an intermediate layer of pink fibres between them (Alami-Durante et al 2010a). Changes in the somatic growth of fish are mainly attributable to changes in total white muscle growth, which is the result of muscle hypertrophy (i.e. increase in the size of existing muscle fibres) and/or hyperplasia (i.e. recruitment of new muscle fibres).
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