Substrate Interactions and Free-Swimming Dynamics in the Crayfish Escape Response.

The caridoid or "tail flip" escape behavior of decapod crustaceans is a model system in neurobiology, but many aspects of its biomechanics are not well understood. To understand how the freshwater virile crayfish Faxonius virilis interacts with the substrate during the tail flip, we studied tail-flip hydrodynamics and force generation for free-moving animals standing on substrate, as well as tethered animals held at different distances from the substrate. We found no significant differences in force generation when distance from substrate was varied. Particle image velocimetry revealed that vortex formation was similar at all distances, but there were notable differences in interactions between shed vortices and substrate at different distances. Negative vorticity (clockwise flow of water) was observed in tethered animals interacting with the substrate but was largely absent in free-swimming animals. We found no evidence of ground effects enhancing tail flip performance in either tethered or free-swimming individuals, as peak force generation occurred before vortex shedding. This study contributes to our understanding of the crayfish escape response and highlights the need for more work that incorporates free-swimming animals and complex environments in the study of crustacean biomechanics.

La reacción de escape caridoide de los crustáceos decápodos, o "coletazo," es un sistema modelo en la neurobiología. Múltiples aspectos de su biomecánica siguen sin explicación. Para entender como el cangrejo de río de agua dulce Faxonius virilis interacciona con el substrato durante el coletazo, hemos estudiado la hidrodinámica y la generación de fuerza del coletazo en animales de movimiento libre parados sobre el substrato, al igual que en animales restringidos a varias distancias por encima del substrato. No hemos detectado ninguna diferencia significativa en la generación de fuerza cuando la distancia del substrato es variada. La velocimetría por imagen de partículas (PIV) ha revelado que la formación de vórtices es similar a todas las distancias, pero existen diferencias notables en las interacciones entre vórtices desprendidos y substrato a diferentes distancias. Hemos observado una vorticidad negativa en animales restringidos interactuando con el substrato, pero no en animales con libre movimiento. No hemos detectado que efectos relacionados al suelo aumenten el rendimiento del coletazo en individuos libres o restringidos, ya que la generación de fuerza máxima ocurrió antes del desprendimiento de los vórtices. Este estudio contribuye al entendimiento de la reacción de escape de los cangrejos de río, y destaca también la necesidad de estudios adicionales que incorporen animales con capacidad de movimiento libre y en ambientes complejos para el estudio de la biomecánica de los crustáceos.

Phytoestrogens ß -sitosterol and genistein have limited effects on reproductive endpoints in a female fish, Betta splendens.

Phytoestrogens are produced by plants and may cause endocrine disruption in vertebrates. The present study hypothesizes that phytoestrogen exposure of female Siamese fighting fish (Betta splendens) may disrupt endogenous steroid levels, change agonistic behavior expression, and potentially also disrupt oocyte development. However, only the pharmacologic dose of ß-sitosterol had a significant effect on opercular flaring behavior, while we did not find significant effects of ß-sitosterol or genistein on steroids or gonads. These findings are in direct contrast with previous studies on the effects of phytoestrogens in female fish. Results of the current study support previous work showing that the effects of phytoestrogen exposure may be less acute in mature female B. splendens than in other fish.

The effects of temperature and dissolved oxygen on antioxidant defences and oxidative damage in the fathead minnow Pimephales promelas.

Fathead minnows Pimephales promelas maintained at 25° C for 6 h had significantly higher superoxide dismutase (SOD) activity than fish maintained at 7 or 32° C, but hypoxic conditions (3 mg l(-1) O2 ) over the same time period did not affect SOD activity. Fish in better body condition (length-adjusted mass) had higher SOD activity. In a separate experiment, P. promelas maintained at three water temperatures (7, 23 and 32° C) for 31 days did not differ in liver acrolein, a biomarker of oxidative stress.

The effect of body coloration and group size on social partner preferences in female fighting fish (Betta splendens).

Females of the fighting fish Betta splendens have been shown to associate with other B. splendens females in a manner reminiscent of shoaling behavior. Since body coloration varies dramatically in this species, and since body coloration has been shown to affect shoalmate choice in other species of fish, we examined the influence of body coloration on association preferences in female B. splendens. In dichotomous choice tests, B. splendens females spent more time swimming near groups of females (regardless of coloration) than swimming near an empty chamber, and chose to swim near fish of similar coloration to their own when choosing between two distinctly colored groups of females. When examining the interplay between body coloration and group size, focal fish spent more time swimming near larger groups (N=5) of similarly colored fish than swimming near an individual female of similar coloration. However, focal fish showed no preference when presented with an individual female of similar coloration and a larger group of females of dissimilar coloration. These results suggest that association choices in B. splendens females are strongly affected by both body coloration and by group size.

Social partner preferences of male and female fighting fish (Betta splendens).

While the social interactions of Betta splendens have been studied in the contexts of dominance hierarchies, mate choice and communication networks, the social partner preferences of Betta have been largely overlooked. In this study, we presented male and female Betta with a single male, a single female, and a group of three females in dichotomous choice tests in order to better understand basic social interactions in this largely nonsocial species. The highly territorial Betta preferred associating with conspecifics in nearly every configuration we tested, with exceptions noted when single females were given the choice between a lone male and an empty chamber, and when males were presented with a single female and an empty chamber. Also, in most tests, the fish chose to spend more time with the larger group of females. The motivation for this preference certainly varied from reproductive to anti-predator. While such behavior might not suggest true shoaling behavior, it does demonstrate a subtle degree of sociality.