A fluid-driven soft robotic fish inspired by fish muscle architecture

Artificial fish-like robots developed to date often focus on the external morphology of fish and have rarely addressed the contribution of the structure and morphology of biological muscle. However, biological studies have proven that fish utilize the contraction of muscle fibers to drive the protective flexible connective tissue to swim. This paper introduces a pneumatic silicone structure prototype inspired by the red muscle system of fish and applies it to the fish-like robot named Flexi-Tuna. The key innovation is to make the fluid-driven units simulate the red muscle fiber bundles of fish and embed them into a flexible tuna-like matrix. The driving units act as muscle fibers to generate active contraction force, and the flexible matrix as connective tissue to generate passive deformation. Applying alternant pressure to the driving units can produce a bending moment, causing the tail to swing. As a result, the structural design of Flexi-Tuna has excellent bearing capacity compared with the traditional cavity-type and keeps the body smooth. On this basis, a general method is proposed for modeling the fish-like robot based on the independent analysis of the active and passive body, providing a foundation for Flexi-Tuna’s size design. Followed by the robot’s static and underwater dynamic tests, we used finite element static analysis and fluid numerical simulation to compare the results. The experimental results showed that the maximum swing angle of the tuna-like robot reached 20°, and the maximum thrust reached 0.185 N at the optimum frequency of 3.5 Hz. In this study, we designed a unique system that matches the functional level of biological muscles. As a result, we realized the application of fluid-driven artificial muscle to bionic fish and expanded new ideas for the structural design of flexible bionic fish.

A higher mitochondrial content is associated with greater oxidative damage, oxidative defenses, protein synthesis and ATP turnover in resting skeletal muscle

ABSTRACT An unavoidable consequence of aerobic metabolism is the production of reactive oxygen species (ROS). Mitochondria have historically been considered the primary source of ROS; however, recent literature has highlighted the uncertainty in primary ROS production sites and it is unclear how variation in mitochondrial density influences ROS-induced damage and protein turnover. Fish skeletal muscle is composed of distinct, highly aerobic red muscle and anaerobic white muscle, offering an excellent model system in which to evaluate the relationship of tissue aerobic capacity and ROS-induced damage under baseline conditions. The present study used a suite of indices to better understand potential consequences of aerobic tissue capacity in red and white muscle of the pinfish, Lagodon rhomboides. Red muscle had a 7-fold greater mitochondrial volume density than white muscle, and more oxidative damage despite also having higher activity of the antioxidant enzymes superoxide dismutase and catalase. The dominant protein degradation system appears to be tissue dependent. Lysosomal degradation markers and autophagosome volume density were greater in white muscle, while ubiquitin expression and 20S proteasome activity were significantly greater in red muscle. However, ubiquitin ligase expression was significantly higher in white muscle. Red muscle had a more than 2-fold greater rate of translation and total ATP turnover than white muscle, results that may be due in part to the higher mitochondrial density and the associated increase in oxidative damage. Together, these results support the concept that an elevated aerobic capacity is associated with greater oxidative damage and higher costs of protein turnover.

Histological and biochemical evaluation of skeletal muscle in the two salmonid species Coregonus maraena and Oncorhynchus mykiss

The growth of fishes and their metabolism is highly variable in fish species and is an indicator for fish fitness. Therefore, somatic growth, as a main biological process, is ecologically and economically significant. The growth differences of two closely related salmonids, rainbow trout (Oncorhynchus mykiss) and maraena whitefsh (Coregonus maraena), have not been adequately studied as a comparative study and are therefore insufficiently understood. For this reason, our aim was to examine muscle growth in more detail and provide a first complex insight into the growth and muscle metabolism of these two fish species at slaughter size. In addition to skeletal muscle composition (including nuclear counting and staining of stem and progenitor cells), biochemical characteristics, and enzyme activity (creatine kinase, lactate dehydrogenase, isocitrate dehydrogenase) of rainbow trout and maraena whitefish were determined. Our results indicate that red muscle contains cells with a smaller diameter compared to white muscle and those fibres had more stem and progenitor cells as a proportion of total nuclei. Interestingly, numerous interspecies differences were identified; in rainbow trout muscle RNA content, intermediate fibres and fibre diameter and in whitefish red muscle cross-sectional area, creatine kinase activity were higher compared to the other species at slaughter weight. The proportional reduction in red muscle area, accompanied by an increase in DNA content and a lower activity of creatine kinase, exhibited a higher degree of hypertrophic growth in rainbow trout compared to maraena whitefish, which makes this species particularly successful as an aquaculture species.

Temperature effects on the contractile performance and efficiency of oxidative muscle from a eury- vs. stenothermal salmonid

We compared the thermal sensitivity of oxidative muscle function between the eurythermal Atlantic salmon (Salmo salar) and the more stenothermal Arctic char (Salvelinus alpinus; which prefers cooler waters). Power output was measured in red skeletal muscle strips and myocardial trabeculae, and efficiency (net work/energy consumed) was measured for trabeculae, from cold (6oC) and warm (15oC) acclimated fish at temperatures from 2-26oC. The mass-specific net power produced by char red muscle was greater than in salmon, by 2-5 fold depending on test temperature. Net power first increased, then decreased, when the red muscle of 6oC-acclimated char was exposed to increasing temperature. Acclimation to 15oC significantly impaired mass-specific power in char (by ∼40-50%) from 2 to 15oC, but lessened its relative decrease between 15 and 26oC. In contrast, maximal net power increased, and then plateaued, with increasing temperature in salmon from both acclimation groups. Increasing test temperature resulted in a ∼3-5 fold increase in maximal net power produced by ventricular trabeculae in all groups, and this effect was not influenced by acclimation temperature. Nonetheless, lengthening power was higher in trabeculae from warm acclimated char, and char trabeculae could not contract as fast as those from salmon. Finally, the efficiency of myocardial net work was approximately 2-fold greater in 15oC acclimated salmon than char (∼15 vs. 7%), and highest at 20oC in salmon. This study provides several mechanistic explanations as to their inter-specific difference in upper thermal tolerance, and potentially why southern char populations are being negatively impacted by climate change.

Skeletal muscle and cardiac transcriptomics of a regionally endothermic fish, the Pacific bluefin tuna, Thunnus orientalis

Background The Pacific bluefin tuna (Thunnus orientalis) is a regionally endothermic fish that maintains temperatures in their swimming musculature, eyes, brain and viscera above that of the ambient water. Within their skeletal muscle, a thermal gradient exists, with deep muscles, close to the backbone, operating at elevated temperatures compared to superficial muscles near the skin. Their heart, by contrast, operates at ambient temperature, which in bluefin tunas can range widely. Cardiac function in tunas reduces in cold waters, yet the heart must continue to supply blood for metabolically demanding endothermic tissues. Physiological studies indicate Pacific bluefin tuna have an elevated cardiac capacity and increased cold-tolerance compared to warm-water tuna species, primarily enabled by increased capacity for sarcoplasmic reticulum calcium cycling within the cardiac muscles. Results Here, we compare tissue-specific gene-expression profiles of different cardiac and skeletal muscle tissues in Pacific bluefin tuna. There was little difference in the overall expression of calcium-cycling and cardiac contraction pathways between atrium and ventricle. However, expression of a key sarcoplasmic reticulum calcium-cycling gene, SERCA2b, which plays a key role maintaining intracellular calcium stores, was higher in atrium than ventricle. Expression of genes involved in aerobic metabolism and cardiac contraction were higher in the ventricle than atrium. The two morphologically distinct tissues that derive the ventricle, spongy and compact myocardium, had near-identical levels of gene expression. More genes had higher expression in the cool, superficial muscle than in the warm, deep muscle in both the aerobic red muscle (slow-twitch) and anaerobic white muscle (fast-twitch), suggesting thermal compensation. Conclusions We find evidence of widespread transcriptomic differences between the Pacific tuna ventricle and atrium, with potentially higher rates of calcium cycling in the atrium associated with the higher expression of SERCA2b compared to the ventricle. We find no evidence that genes associated with thermogenesis are upregulated in the deep, warm muscle compared to superficial, cool muscle. Heat generation may be enabled by by the high aerobic capacity of bluefin tuna red muscle.

Distribution of Metals in Red and White Axial Muscles of Three Fish Species from the Krasnoyarsk Reservoir

The content of metals in fish fillet is an important criterion for food safety and nutritional benefits. Fish fillet is composed of both white and red muscles, but the standard method only detects metal content in white muscle. The true metal content in fish fillet can be underestimated due to this approach. So far, metal content in different types of muscle tissue of freshwater fish remains virtually unstudied. The aim of the present research was to study the metal content in red and white muscles of roach Rutilus rutilus, bream Abramis brama and pike Esox lucius that live in the Krasnoyarsk reservoir. Twenty metals were measured in the dry mass of red and white muscles of three fish species using inductively coupled plasma (ICP-OES) spectrometry. The contents of macronutrients such as K, Ca and Mg were higher in white muscle fibers and Na – in red fibers. Of the 16 metals regarded as trace elements, the highest contents in the muscles were noted for Fe (20.5-177.8 μg/g), Zn (26.7-79.0 μg/g), and Al (15.2- 67.2 μg/g), regardless of the fish species and type of tissue. Li (0.01-0.09 μg/g) and Cd (0.01-0.03 μg/g) had the lowest concentrations. Among trace elements, the contents of Cu and Fe were significantly higher in the dry biomass of red muscle compared with white muscle for the three fish species. The content of Zn was higher in the red muscle of bream and pike. Almost all other trace elements also tended to accumulate in higher concentrations in the red muscle. Differences between red and white muscles in the contents of trace elements such as Pb and Sr were species-specific. The distribution of metals between the two types of muscle fibers demonstrated by the freshwater species examined in this study was similar to the distribution of metals in marine fish, except the distribution of Sr. Thus, the greater capacity of the red muscle for accumulating most heavy metals confirmed in the present study may indicate a greater risk to health in eating this type of tissue