Early decrease in dietary protein:energy ratio by fat addition and ontogenetic changes in muscle growth mechanisms of rainbow trout: short- and long-term effects

Growth, survival, and myogenic gene expression in the post-larvae of Colossoma macropomum provisioned with Artemia nauplii

Artemia nauplii are widely used as fish larvae feed due to its beneficial nutritional characteristics for larval development; however, efficient feeding strategies are needed to balance its high costs. Therefore, we evaluated the effects of different densities of Artemia nauplii (100, 250, 500, 750, and 1000 nauplii/post-larvae) on the growth, survival, water quality, and myogenic gene expression of tambaqui (Colossoma macropomum) post-larvae cultivated in a recirculating aquaculture system. After 2 weeks of trial, there was a significant decrease in dissolved oxygen concentration with the increase in nauplii density, but it did not interfere with larval performance and survival. In the first week, larvae fed with fewer than 500 nauplii/post-larvae presented slower growth, while in the second week, larvae fed with 1000 nauplii/post-larvae had the highest final weight and length. Regression analysis suggests that the optimum feeding density of Artemia nauplii during the first week is 411 nauplii/post-larvae, while for the second week, the growth increased proportionally to the feeding densities. The relative expression of the myod, myog, and mstn genes was higher in larvae fed with fewer than 500 nauplii/post-larvae. Although low-growing larvae showed increased expression of myod and myog genes, responsible for muscle hyperplasia and hypertrophy, respectively, mstn expression may have played a significant inhibitory role in larval development. Further research is needed to better determine the effects of the live food on the zootechnical performance and the expression of the myogenic genes in the initial phase of the life cycle of the tambaqui post-larvae.

Protein Requirements of Oncorhynchus mykiss Cultured in the Convection-Water Cages by Evaluating Growth, Body Composition and Liver Health

The diet formulation for trout has changed dramatically over the last decade due to changes in the ingredient markets and advances in feed processing technology. The protein requirements of Oncorhynchus mykiss were established at the end of the last century, and it is unclear whether these requirements are applicable to modern dietary formulations. Therefore, an eight-week feeding trial was performed to measure the protein requirements of O. mykiss by evaluating growth, body composition, antioxidation property, innate immune response and liver morphology. The five experimental diets were prepared to contain the same levels of crude lipid (120 g/kg) and graded levels of crude protein (356.3, 383.9, 411.5, 439.2 and 466.8 g/kg). The results suggested that the growth, feed utilization and whole-body crude protein levels were significantly increased when fish were fed diets containing 439.2 and 466.8 g/kg crude protein. Meanwhile, low dietary protein levels (356.3 and 383.9 g/kg) significantly down-regulated the mRNA levels of insulin-like growth factor I, catalase, glutathione peroxidase, superoxide dismutase, complement 3 and lysozyme, and also up-regulated the insulin-like growth factor binding protein 1 as well as proinflammatory cytokine expression in the liver, including interleukin 1β, interleukin 8 and tumor necrosis factor-α. Moreover, low dietary protein levels (356.3 and 383.9 g/kg) damaged liver structure, suppressed total antioxidative capacity and increased the malondialdehyde content in liver. In conclusion, high dietary protein (439.2 and 466.8 g/kg) promoted fish growth, while low dietary protein (356.3 and 383.9 g/kg) damaged liver structure, induced oxidative stress and inflammatory responses and weakened non-specific immunity. The protein requirement of O. mykiss reared in the convection-water cages is no less than 439.2 g/kg for optimal growth, antioxidant and immune properties.

Intestinal Microbiota Regulate Certain Meat Quality Parameters in Chicken

Growing evidence of intestinal microbiota-muscle axis provides a possibility to improve meat quality of broilers through regulating intestinal microbiota. Water-holding capacity is a crucial factor to evaluate the meat quality. High quality of water-holding capacity is usually described as a low drip-losing rate. This study aimed to explore the relationship between intestinal microbiota and water-holding capacity of muscle in broilers. According to our results, two native breeds of broilers (the Arbor Acres broilers and the Beijing-You broilers) exhibited remarkable differences in microbiota composition. However, the regular of gut bacteria compositions gradually became similar when the two breeds of broiler were raised in a same feeding environment. Therefore, this similar regular of intestinal microbiota induced similar water-holding capacity of the muscle from the two breeds. In subsequent fecal microbiota transplantation (FMT) experiments, the intestinal microbiota community of the Arbor Acres broilers was remodeling by oral gavage of bacterial suspension that was derived from the Beijing-You broilers. Then, not only body weight and abdominal fat rate were increased, but also drip loss of muscle was decreased in the Arbor Acres broilers. Additionally, muscle fiber diameter of biceps femoris muscle and expression of MyoD1 were notably enlarged. Muscle fiber diameter and related genes were deemed as important elements for water-holding capacity of muscle. Simultaneously, we screened typical intestinal bacteria in both the two native breeds of broilers by 16S rDNA sequencing. Lachnoclostridium was the only bacteria genus associated with drip-losing rate, meat fiber diameter, body weight, and abdominal fat rate.

Dietary Selenium Promotes Somatic Growth of Rainbow Trout (Oncorhynchus mykiss) by Accelerating the Hypertrophic Growth of White Muscle

As a nutritionally essential trace element, selenium (Se) is crucial for fish growth. However, the underlying mechanisms remain unclear. Fish somatic growth relies on the white muscle growth. This study aimed to explore the effects and underlying mechanisms of Se on fish white muscle growth using a juvenile rainbow trout (Oncorhynchus mykiss) model. Fish were fed a basal diet unsupplemented or supplemented with selenium yeast at nutritional dietary Se levels (2 and 4 mg/kg Se, respectively) for 30 days. Results showed that dietary Se supplementation significantly enhanced trout somatic growth. Histological and molecular analysis of trout white muscle tissues at the vent level showed that dietary Se supplementation elevated the total cross-sectional area of white muscle, mean diameter of white muscle fibers, protein content, nuclei number, and DNA content of individual muscle fiber, and suppressed the activities of calpain system and ubiquitin-proteasome pathway. Overall, this study demonstrated that dietary Se within the nutritional range inhibits calpain- and ubiquitin-mediated protein degradation and promotes the fusion of myoblasts into the existed muscle fibers to promote the hypertrophic growth of white muscle, thereby accelerating the somatic growth of rainbow trout. Our results provide a mechanistic insight into the regulatory role of Se in fish growth.

Retention of learned predator recognition in embryonic and juvenile rainbow trout

Minimizing predation risk, especially for young or naïve individuals, can be achieved by learning to recognize predators. Embryonic learning may optimize survival by allowing for the earliest possible response to predation threats posthatch. However, predatory threats often change over an individual’s lifetime, and using old information can be detrimental if it becomes outdated. Adaptive forgetting allows an individual to discount obsolete information in decision-making and instead emphasize newer, more relevant information when responding to predation threats. Little is known about the extent to which young individuals can learn and forget information about predation threats. Here we demonstrate that rainbow trout 1) are capable of learning from both conspecific and heterospecific alarm cues as embryos, newly hatched larvae, and free-swimming larvae, 2) exhibit adaptive forgetting of predator information at all stages, and 3) display dynamic adaptive forgetting based on the ontogeny of learning. Specifically, fish that learned information as embryos retained the information for longer periods than those that learned the same information as newly hatched alevins.

The increase in fiber size in male rat gastrocnemius after chronic central leptin infusion is related to activation of insulin signaling

Insulin potentiates leptin effects on muscle accrual and glucose homeostasis. However, the relationship between leptin's central effects on peripheral insulin sensitivity and the associated structural changes remain unclear. We hypothesized that central leptin infusion modifies muscle size through activation of insulin signaling. Muscle insulin signaling, enzymes of fatty acid metabolism, mitochondrial respiratory chain complexes, proliferating cell nuclear antigen (PCNA) and fiber area were analyzed in the gastrocnemius of chronic central infused (L), pair-fed (PF) and control rats. PCNA-positive nuclei, fiber area, GLUT4 and glycogen levels and activation of Akt and mechanistic target of rapamycin were increased in L, with no changes in PF. Acetyl-CoA carboxylase-β mRNA levels and non-esterified fatty acid and triglyceride content were reduced and carnitine palmitoyltransferase-1b expression and mitochondrial complexes augmented in L. These results suggest that leptin promotes an increase in muscle size associated with improved insulin signaling favored by lipid profile.

Transient up- and down-regulation of expression of myosin light chain 2 and myostatin mRNA mark the changes from stratified hyperplasia to muscle fiber hypertrophy in larvae of gilthead sea bream (Sparus aurata L.)

Hyperplasia and hypertrophy are the two mechanisms by which muscle develops and grows. We study these two mechanisms, during the early development of white muscle in Sparus aurata, by means of histology and the expression of structural and regulatory genes. A clear stage of stratified hyperplasia was identified early in the development of gilthead sea bream but ceased by 35 dph when hypertrophy took over. Mosaic recruitment of new white fibers began as soon as 60 dph. The genes mlc2a and mlc2b were expressed at various levels during the main phases of hyperplasia and hypertrophy. The genes myog and mlc2a were significantly up-regulated during the intensive stratified formation of new fibers and their expression was significantly correlated. Expression of mstn1 and igf1 increased at 35 dph, appeared to regulate the hyperplasia-to-hypertrophy transition, and may have stimulated the expression of mlc2a, mlc2b and col1a1 at the onset of mosaic hyperplasia. The up-regulation of mstn1 at transitional phases in muscle development indicates a dual regulatory role of myostatin in fish larval muscle growth.