Valentina Di Santo

Phototactic guidance of a tissue-engineered soft-robotic ray

Swim into the light A bio-inspired swimming robot that mimics a ray fish can be guided by light. Park et al. built a 1/10th-scale version of a ray fish with a microfabricated gold skeleton and a rubber body powered by rat heart muscle cells. The cardiomyocytes were genetically engineered to respond to light cues, so that the undulatory movements propelling the robot through water would follow a light source. Science, this issue p. 158 A biohybrid swimming robot powered by cardiomyocytes is optogenetically engineered to respond to light cues. Inspired by the relatively simple morphological blueprint provided by batoid fish such as stingrays and skates, we created a biohybrid system that enables an artificial animal—a tissue-engineered ray—to swim and phototactically follow a light cue. By patterning dissociated rat cardiomyocytes on an elastomeric body enclosing a microfabricated gold skeleton, we replicated fish morphology at 110 scale and captured basic fin deflection patterns of batoid fish. Optogenetics allows for phototactic guidance, steering, and turning maneuvers. Optical stimulation induced sequential muscle activation via serpentine-patterned muscle circuits, leading to coordinated undulatory swimming. The speed and direction of the ray was controlled by modulating light frequency and by independently eliciting right and left fins, allowing the biohybrid machine to maneuver through an obstacle course.

Intraspecific variation in physiological performance of a benthic elasmobranch challenged by ocean acidification and warming

ABSTRACT Elucidating the combined effects of increasing temperature and ocean acidification on performance of fishes is central to our understanding of how species will respond to global climate change. Measuring the metabolic costs associated with intense and short activities, such as those required to escape predators, is key to quantifying changes in performance and estimating the potential effects of environmental stressors on survival. In this study, juvenile little skate Leucoraja erinacea from two neighboring locations (Gulf of Maine, or northern location, and Georges Bank, or southern location) were developmentally acclimatized and reared at current and projected temperatures (15, 18 or 20°C) and acidification conditions (pH 8.1 or 7.7), and their escape performance was tested by employing a chasing protocol. The results from this study suggest countergradient variation in growth between skates from the two locations, while the optimum for escape performance was at a lower temperature in individuals from the northern latitudes, which could be related to adaptation to the local thermal environment. Aerobic performance and scope declined in skates from the northern latitudes under simulated ocean warming and acidification conditions. Overall, the southern skates showed lower sensitivity to these climatic stressors. This study demonstrates that even mobile organisms from neighboring locations can exhibit substantial differences in energetic costs of exercise and that skates from the northern part of the geographic range may be more sensitive to the directional increase in temperature and acidification expected by the end of the century. Summary: Juvenile little skates from neighboring locations, developmentally acclimatized to varying levels of ocean acidification and warming, exhibit substantial differences in escape and aerobic performance.

Swimming Mechanics and Energetics of Elasmobranch Fishes

1. Introduction 2. Elasmobranch Locomotor Diversity 3. Elasmobranch Kinematics and Body Mechanics 4. Hydrodynamics of Elasmobranch Locomotion 5. The Remarkable Skin of Elasmobranchs and Its Locomotor Function 6. Energetics of Elasmobranch Locomotion 7. Climate Change: Effects on Elasmobranch Locomotor Function 8. Conclusions The remarkable locomotor capabilities of elasmobranch fishes are evident in the long migrations undertaken by many species, in their maneuverability, and in specialized structures such as the skin and shape of the pectoral and caudal fins that confer unique locomotor abilities. Elasmobranch locomotor diversity ranges from species that are primarily benthic to fast open-ocean swimmers, and kinematics and hydrodynamics are equally diverse. Many elongate-bodied shark species exhibit classical undulatory patterns of deformation, while skates and rays use their expanded wing-like locomotor structures in oscillatory and undulatory modes. Experimental hydrodynamic analysis of pectoral and caudal fin function in leopard sharks shows that pectoral fins, when held in the typical cruising position, do not generate lift forces, but are active in generating torques during unsteady swimming. The heterocercal (asymmetrical) tail shape generates torques that would rotate the body around the center of mass except for counteracting torques generated by the ventral body surface and head. The skin of sharks, with its hard surface denticles embedded in a flexible skin, alters flow dynamics over the surface and recent experimental data suggest that shark skin both reduces drag and enhances thrust on oscillating propulsive surfaces such as the tail. Analyses of elasmobranch locomotor energetics are limited in comparison to data from teleost fishes, and data from batoids are particularly scarce. We present an overview of comparative data on elasmobranch energetics, with comparisons to selected teleost fishes: generally, teleost fishes exhibit low costs of transport compared to elasmobranchs. Many elasmobranch species are particularly susceptible to changing oceanic conditions in response to climate change as a result of benthic habitat, reproductive mode, or reproductive site fidelity. Experimental studies on skates demonstrate that even small changes in water temperature can negatively impact locomotor performance, and locally adapted populations can differ in how they respond to abiotic stressors.

Batoid locomotion: effects of speed on pectoral fin deformation in the little skate, Leucoraja erinacea

ABSTRACT Most batoids have a unique swimming mode in which thrust is generated by either oscillating or undulating expanded pectoral fins that form a disc. Only one previous study of the freshwater stingray has quantified three-dimensional motions of the wing, and no comparable data are available for marine batoid species that may differ considerably in their mode of locomotion. Here, we investigate three-dimensional kinematics of the pectoral wing of the little skate, Leucoraja erinacea, swimming steadily at two speeds [1 and 2 body lengths (BL) s−1]. We measured the motion of nine points in three dimensions during wing oscillation and determined that there are significant differences in movement amplitude among wing locations, as well as significant differences as speed increases in body angle, wing beat frequency and speed of the traveling wave on the wing. In addition, we analyzed differences in wing curvature with swimming speed. At 1 BL s−1, the pectoral wing is convex in shape during the downstroke along the medio-lateral fin midline, but at 2 BL s−1 the pectoral fin at this location cups into the flow, indicating active curvature control and fin stiffening. Wing kinematics of the little skate differed considerably from previous work on the freshwater stingray, which does not show active cupping of the whole fin on the downstroke. Summary: Three-dimensional analysis of pectoral fin movement in the little skate during swimming reveals substantial changes in shape as speed increases.

Skating by: low energetic costs of swimming in a batoid fish

ABSTRACT We quantify the oxygen consumption rates and cost of transport (COT) of a benthic batoid fish, the little skate, Leucoraja erinacea, at three swimming speeds. We report that this species has the lowest mass-adjusted swimming metabolic rate measured for any elasmobranch; however, this species incurs a much higher COT at approximately five times the lowest values recorded for some teleosts. In addition, because skates lack a propulsive caudal fin and could not sustain steady swimming beyond a relatively low optimum speed of 1.25 body lengths s−1, we propose that the locomotor efficiency of benthic rajiform fishes is limited to the descending portion of a single COT–speed relationship. This renders these species poorly suited for long-distance translocation and, therefore, especially vulnerable to regional-scale environmental disturbances. Summary: The little skate exhibits decreasing mass-adjusted swimming metabolic rates with increasing speed, which are the lowest values among elasmobranchs. However, its cost of transport is one of the highest measured for fishes.

Progressive hypoxia decouples activity and aerobic performance of skate embryos

We evaluated the usefulness of long-term plant carbon economy of a xerophyte shrub as a tool in conservation. Reserves manipulation through defoliation decreased reproduction in the long-term but not growth. Root and shoot reserves can be used as indicators of how much biomass can be harvested without threatening future reproduction

High postural costs and anaerobic metabolism during swimming support the hypothesis of a U-shaped metabolism–speed curve in fishes

Significance Hydrodynamic theory predicts that the energetic costs required for fishes to swim should vary with speed according to a U-shaped curve, with an expected energetic minimum at intermediate cruising speeds. Empirical studies to date do not support this view. Here we report a complete dataset on a swimming batoid fish that shows a clear energetic minimum at intermediate swimming speeds. We also demonstrate that this species uses a combination of aerobic and anaerobic metabolism to fuel steady swimming at each speed, including the slowest speeds tested. This contradicts the widespread assumption that fish use only aerobic metabolism at low speeds. Kinematic data support this nonlinear relationship by also showing a U-shaped pattern to body angle during steady swimming. Swimming performance is considered a key trait determining the ability of fish to survive. Hydrodynamic theory predicts that the energetic costs required for fishes to swim should vary with speed according to a U-shaped curve, with an expected energetic minimum at intermediate cruising speeds and increasing expenditure at low and high speeds. However, to date no complete datasets have shown an energetic minimum for swimming fish at intermediate speeds rather than low speeds. To address this knowledge gap, we used a negatively buoyant fish, the clearnose skate Raja eglanteria, and took two approaches: a classic critical swimming speed protocol and a single-speed exercise and recovery procedure. We found an anaerobic component at each velocity tested. The two approaches showed U-shaped, though significantly different, speed–metabolic relationships. These results suggest that (i) postural costs, especially at low speeds, may result in J- or U-shaped metabolism–speed curves; (ii) anaerobic metabolism is involved at all swimming speeds in the clearnose skate; and (iii) critical swimming protocols might misrepresent the true costs of locomotion across speeds, at least in negatively buoyant fish.

Thermal tolerance of the invasive red-bellied pacu and the risk of establishment in the United States

Indigenous red-bellied pacu, Piaractus brachypomus, populations are in decline due to overfishing. Once ignored by aquaculturists because of their perceived low economic value, renewed aquaculture efforts in Central and South America aim to relieve fishing pressures on natural pacu populations. In the southern United States pacu aquaculture for the aquarium trade has raised concerns that accidental release could lead to establishment of overwintering populations outside captivity-a threat accentuated by the average 6 °C increase in shallow-water temperatures predicted by the end of the century. In the present study, Critical and Chronic Thermal Methodology was used to quantify red-bellied pacu thermal tolerance niche requirements. The data suggest that red-belllied pacu are a thermophilic species capable of tolerating low and high chronic temperatures of 16.5 °C and 35 °C, respectively. Critical thermal minimum and maximum temperatures of fish acclimated near their chronic limits are 10.3 and 44.4 °C. Red-bellied pacu aquaculture in the United States is concentrated in subtropical Florida regions that encourage rapid growth and reproduction, but carry an increased risk of establishing reproducing populations in local freshwater systems. The thermal niche data show that the risk of bioinvasion can be reduced or eliminated by adopting an approach whereby aquaculture potential is integrated with environmental temperature constraints.