Survivorship of zebrafish, Danio rerio, was measured during lethal hypoxic stress after pretreatment in water at either ambient oxygen or at a lowered, but nonlethal, level of oxygen. Acclimation to nonlethal hypoxia (pO2 ≅ 15 Torr; ca. 10% air‐saturation) for 48 hr significantly extended survival time during more severe hypoxia (pO2 ≅ 8 Torr; ca. 5% air‐saturation) compared to survival of individuals with no prior hypoxic exposure. The magnitude of the acclimation effect depended upon the sex of the fish: hypoxia pretreatment increased the survival times of males by a factor of approximately 9 and that of females by a factor of 3 relative to controls. In addition, survival time of control and hypoxia acclimated fish depended upon when in the year experiments were conducted. Survival times were 2–3 times longer when measured in the late fall or winter compared to survival times measured during the spring or summer. These results demonstrate a direct survival benefit of short‐term acclimation to hypoxia in this genetically tractable fish. The fact that the acclimation effect depended upon the sex of the fish and the season during which experiments were conducted demonstrates that other genetic and/or environmental factors affect hypoxia tolerance in this species. J. Exp. Zool. 289:266–272, 2001. © 2001 Wiley‐Liss, Inc.

No abstract

A modeling study was conducted to determine if the expansion of invasive northern snakehead Channa argus could negatively affect the largemouth bass Micropterus salmoides population size in Potomac River (Chesapeake Bay). Current distributions for both species were generated using catch records. Northern snakehead was not widely distributed during the study period and occurred mainly in upstream areas of tributaries. Many of these areas were moderately or highly suitable habitats for largemouth bass. Of sites where juvenile largemouth bass were collected, 10.6% were associated with northern snakehead. Using population modeling and measured predator–prey interactions, we determined that this level of co‐occurrence would result in a 3.8% reduction in largemouth bass population size. This prediction is consistent with current observations that indicate there has not been a negative trend in the largemouth bass fishery. As co‐occurrence was increased in the model, however, the negative impact of northern snakehead on largemouth bass monotonically increased. The time required for such increases in northern snakehead distribution is not known. If northern snakehead continues to expand its range in the absence of control measures, then our population model, with its assumptions, predicts a 35.5% reduction in the abundance of largemouth bass in the Potomac River. Received February 6, 2012; accepted June 7, 2012

Most fishes known for terrestrial locomotion are small and/or elongate. Northern snakeheads (Channa argus) are large, air-breathing piscivores anecdotally known for terrestrial behaviors. Our goals were to determine their environmental motivations for emersion, describe their terrestrial kinematics for fish 3.0 to 70.0 cm and compare kinematics among four substrates. For emersion experiments, C. argus were individually placed into aquatic containers with ramps extending through the surface of the water, and exposed to fifteen ecologically-relevant environmental conditions. For kinematic experiments, fish were filmed moving on moist bench liner, grass, artificial turf, and a flat or tilted rubber boat deck. Videos were digitized for analysis in MATLAB and electromyography was used to measure muscular activity. Only the low pH (4.8), high salinity (30 ppt), and high dCO2 (10% seltzer solution) treatments elicited emersion responses. While extreme, these conditions do occur in some of their native Asian swamps. Northern snakeheads >4.5 cm used a unique form of axial-appendage-based terrestrial locomotion involving cyclic oscillations of the axial body, paired with near-simultaneous movements of both pectoral fins. Individuals ≤3.5 cm used tail-flip jumps to travel on land. Northern snakeheads also moved more quickly on complex, three-dimensional substrates (e.g., grass) than on smooth substrates (e.g., bench liner), and when moving downslope. Release of snakeheads onto land by humans or accidentally by predators may be more common than voluntary emersion, but because northern snakeheads can respire air, it may be necessary to factor in the ability to spread overland into the management of this invasive species.