Critical swimming speed, tail-flip speed and physiological response to exercise fatigue in kuruma shrimp, Marsupenaeus japonicus

Hydrodynamics of the fast-start caridoid escape response in Antarctic krill, Euphausia superba

Krill are shrimp-like crustaceans with a high degree of mobility and variety of documented swimming behaviors. The caridoid escape response, a fast-start mechanism unique to crustaceans, occurs when the animal performs a series of rapid abdominal flexions and tail flipping that results in powerful backward strokes. The current results quantify the animal kinematics and three-dimensional flow field around a free-swimming Euphausia superba as it performs the caridoid escape maneuver. The specimen performs a single abdominal flexion-tail flip combination that leads to an acceleration over a 42 ms interval allowing it to reach a maximum speed of 57.0 cm/s (17.3 body lengths/s). The krill's tail flipping during the abdominal closure is a significant contributor to the thrust generation during the maneuver. The krill sheds a complex chain of vortex rings in its wake due to the viscous flow effects while the organism accelerates. The vortex ring structure reveals a strong suction flow in the wake, which suggests that the pressure distribution and form drag play a role in the force balance for this maneuver. Antarctic krill typically swim in a low to intermediate Reynolds number (Re) regime where viscous forces are significant, but as shown by this analysis, its high maneuverability allows it to quickly change its body angle and swimming speed.

Effects of constant flow velocity on endurance swimming and fatigue metabolism in red drum and blackhead seabream

Aquaculture has greater potential for seafood production than wild capture fisheries. To meet the growing demand for seafood, China's marine aquaculture industry has begun building deep-water cages in the open sea. However, under these conditions, fish encounter strong currents and waves, and ensuring their healthy growth is key to the farming process. To address these issues, it is necessary to study the sustained swimming abilities of cultured fish species. Blackhead seabream (Acanthopagrus schlegelii) and red drum (Sciaenops ocellatus) are traditional economic fish species in China; however, their sustained swimming ability under a constant current has been underexplored. Therefore, we examined the endurance swimming ability of three size classes of blackhead seabream and red drum at 20 °C. The fish were then subjected to swimming tests of 0, 30, 60, 90, 120, and 150 min at a constant swimming speed of 0.55 m/s (0.80 m/s), 0.65 m/s (0.90 m/s), and 0.70 m/s (0.98 m/s). The fish were then dissected to obtain muscle, blood, and liver samples; sample metabolite concentrations were measured at six time points, each of which guaranteed five sets of valid data. The results indicated that red drum has a significantly stronger swimming ability, and can be cultured in waters with a short-term flow rate not exceeding 0.75 m/s or 3.5 BL/s. Further, blackhead seabream can be cultured in waters with a flow velocity lower than 0.55 m/s or 2.5 BL/s. The species-related metabolic differences were mainly reflected in the hepatic glycogen and blood glucose concentrations, and those in swimming ability caused by body length were mainly reflected by the hepatic glycogen concentration. The hepatic glycogen concentration had the most significant effect on fish with body lengths >28 cm (P < 0.05). Overall, the experimental results indicated that the liver plays a major role in the physiological level of fish swimming fatigue, providing a direction for further research.

Modulation of stress response and productive performance of Litopenaeus vannamei through diet

The high tolerance of Litopenaeus vannamei to a wide range of salinity (1–50 psu) makes this species an excellent candidate for culture under low salinity, decreasing shrimp epidemics and water pollution in some coastal areas. However, salinity levels outside the optimal range could impose several physiological constraints that would in turn affect growth and survival, particularly in the presence of additional stressors (e.g. high densities, handling practices, and hypoxia). Despite shrimp susceptibility to individual stressors has been widely addressed, information regarding response to chronic and acute stressors combined and its relation to diet is scarce. Thus, the aim of our study was to determine the effect of diet on the susceptibility to chronic (low salinity) and acute (hypoxia and escape response) stressors in terms of culture performance and physiological indicators. We evaluated overall performance during culture of L. vannamei at low salinity (6 psu), fed with an experimental diet with low protein and high carbohydrate content (26% protein and 6% fish meal plus probiotic mixture) and compared to a commercial formula with high protein and low carbohydrate content (40% crude protein and 20% fish meal without probiotic mixture). At the end of the rearing experiment, shrimp were exposed to two types of acute stress, hypoxia and escape. Biochemical (hemocyanin, total proteins, glucose, and lactate) and bioenergetic (adenylic energy charge and arginine phosphate levels) variables were measured to assess chronic stress response (salinity) and acute stress response (hypoxia or escape). The experimental diet resulted in higher muscle energy status that was not affected by low salinity, although lipid levels were lower under this condition. This diet partially counteracted the low performance at low salinity and promoted greater protein efficiency. Hypoxia induced strong hyperglycemic and lactate increase as response, whereas escape response was characterized by a depletion of arginine phosphate levels, with a stronger decrease in shrimp fed experimental diet, due to the high initial level of this reserve. Some data (glucose levels in hemolymph and lipids in hepatopancreas) suggest that shrimp under chronic stress conditions (low salinity and high densities) present a low ability to respond to subsequent acute stressors such as hypoxia or escape. This work indicates that diet can increase the energy status of shrimp, enabling them to overcome potential multifactorial stressors, which are common in farming systems.

Visual Stimuli for the Induction of Hunting Behavior in Cuttlefish Sepia pharaonis

Cuttlefish exhibit typical hunting behavior, including elongating tentacles against specific prey such as prawn and mysid shrimp. Cuttlefish hunting behavior involves three different actions: attention, positioning, and seizure. Hunting behavior is innate and stereotypic behavior, and it is present in newly hatched juveniles. Factors associated with prey are known to induce this behavior, similar to the sign stimulus, whereby young herring chicks imitate pecking behavior against a red dot on their parent's bill. Although the hunting behavior of cuttlefish has been described and used as an indicator to test learning and memory, details of a stimulus that can elicit this behavior remain unknown. Here, we used a variety of visual stimuli presented on a computer screen to investigate the factors that induce hunting behavior of pharaoh cuttlefish, Sepia pharaonis. We found that the appearance of prey (western king prawn, Melicertus latisulcatus) and their movement at a vertical angle of 45° are specific factors that can initiate hunting behavior. We also showed that the height of prey can attract cuttlefish and initiate hunting. To the best of our knowledge, this is the first report of a stimulus that elicits stereotyped hunting behavior by coleoid cephalopods.

Effects of temperature, salinity, body length, and starvation on the critical swimming speed of whiteleg shrimp, Litopenaeus vannamei

The critical swimming speed (U(crit), cms⁻¹) of whiteleg shrimp, Litopenaeus vannamei, exposed to various temperatures (17, 20, 25, and 29 °C), salinities (20, 25, 30, 35, and 40), and starvation days (1, 4, and 8d), was determined in a flume tank. Body length (5.5, 6.6, 7.3, 9.4, and 10.0 cm) was also studied in relation to the U(crit). Temperature, salinity, body length and starvation significantly affected the U(crit) of whiteleg shrimp. The U(crit) increased as temperature increased from 17 to 29 °C. The relationship between temperature (t, °C) and U(crit) can be described by the linear model as U(crit)=1.5916t+0.8892, R²=0.9992 (P<0.01). The U(crit) increased and then decreased as salinity increased from 20 to 40. The optimum salinity and the corresponding maximum U(crit) are 36.17 and 42.87 cms⁻¹, respectively. The relationship between salinity (s) and U(crit) can be described by the quadratic model as U(crit)=-0.0171s²+1.2371s+20.497, R²=0.7667 (P=0.234). The U(crit) increased as body length increased from 5.5 to 10.0 cm, whereas relative critical swimming speed (U(crit)', BLs⁻¹) decreased. The relationship between body length (l, cm) and U(crit) or U(crit)' can be described by the quadratic model as U(crit)=-0.6233l²+12.302l-20.264, R²=0.9942 (P<0.01) or U(crit)'=-0.0514l²+0.5351l+3.8132, R²=0.9862 (P<0.05). The U(crit) decreased as starvation days increased from 1 to 8d. The relationship between starvation day (d, d) and U(crit) can be described by the quadratic model as U(crit)=-0.1262d²-0.0395d +40.979, R²=1. Low temperatures and salinity and starvation can reduce the swimming speed of whiteleg shrimp. Results can be of value in evaluating the locomotive ability, understanding ecological processes, and improving the capture and stock enhancement of whiteleg shrimp.