Thermal performance of the electron transport system Complex III in seven Alabama fishes.

Management of fish populations for conservation in thermally variable systems requires an understanding of the fish's underlying physiology and responses to thermal stress. Physiological research at the organismal level provides information on the overall effects of stressors such as extreme temperature fluctuations. While experiments with whole organisms provide information as to the overall effects of temperature fluctuations, biochemical assays of thermal stress provide direct results of exposure that are both sensitive and specific. Electron transport system (ETS; Complex III) assays quantify a rate-limiting step of respiratory enzymes. Parameters that can be estimated via this approach include optimum thermal temperature (Topt ) and optimal breadth of thermal performance (Tbreadth ), which can both be related to organismal-level temperature thresholds. We exposed enzymes of seven fish species (native fish chosen to represent a typical community in Alabama streams) to temperatures in the range 11-44°C. The resultant enzymatic thermal performance curves showed that Topt , the lower temperature for enzyme optimal thermal performance (Tlow ), the upper temperature for enzyme optimal thermal performance (Tup ), and Tbreadth differed among species. Relationships between enzymatic activity and temperature for all fish followed a pattern of steadily increasing enzyme activity to Topt before gradually decreasing with increasing temperature. A comparison of our enzyme optimum and upper-temperature limit results versus published critical thermal maxima values supports that ETS Complex III assays may be useful for assessing organismal-level thermal tolerance.

THE EFFECTS OF GLOCHIDIA INFECTION ON THE METABOLIC RATE AND HYPOXIA TOLERANCE OF BLUEGILL LEPOMIS MACROCHIRUS AND LARGEMOUTH BASS MICROPTERUS SALMOIDES.

Gill parasites can negatively affect hosts by altering behavior or causing adverse effects to host physiology. Most unionid mussel larvae (glochidia) are obligate parasites requiring fish hosts, but much of the literature concerning how these parasites affect their hosts has been limited to only a few study species of salmonids and mussels. Here, we test the effects of natural glochidia infection levels on resting metabolic rate and hypoxia tolerance of bluegill Lepomis macrochirus and largemouth bass Micropterus salmoides using glochidia of the southern fatmucket mussel Lampsilis straminea, a warm-water unionid. We quantified oxygen uptake, hypoxia tolerance, and ability to regulate metabolic rate via respiration rate, critical dissolved oxygen values (DOcrit), and a regulation index (RI), respectively, to compare the effects of glochidia infection between infected and uninfected fish over 11 wk after host inoculation. Hosts were infected with glochidia at levels similar to those seen in wild, naturally occurring infections. At these levels, we observed no effects of glochidia infection on metabolic rate, DOcrit, or RI of infected versus control fish of either species over our 11-wk experiment. Glochidia infection on fish gills at levels expected under field conditions may not always induce an organismal-level (i.e., individual organism) response or cause host respiratory stress. Preventing respiratory stress from infection would be beneficial for both host and parasite, given that glochidia survival and dispersal depend on host survival.

Choice in the bluegill (Lepomis macrochirus).

To study matching in a species distantly related to mammals and birds, seven bluegill were trained to break a photobeam using a nose-poke response for access to pelleted food in their home aquaria during one-h sessions. Reinforcer ratios available from the two response alternatives varied among the following: 16:1, 8:1, 4:1, 1:1, 1:4, 1:8, and 1:16. The overall reinforcement rate was held at 0.8/min. All experiments were conducted in a closed economy, i.e., the fish's daily food ration was available only during experimental sessions. Matching functions are reported for each fish using all combinations of scheduled and obtained reinforcer ratios as the independent variables and response and time ratios as the dependent variables. All matching functions had slopes less than 1.0 and r(2) values above 0.70. Overall response rates were unrelated to the reinforcer ratios but, as with other species studied, changeover rates were highest for the 1:1 condition and lowest for the 16:1 conditions. These results are consistent with data obtained from more traditionally studied taxa (e.g., birds, mammals, and primates), and similar previous studies with fish, suggesting that matching has been conserved since fish, birds, and mammals evolved from a common ancestor over 400 million years ago.

Predation and the distribution and abundance of a pulmonate pond snail.

The abundances of a freshwater pulmonate snail, Lymnaea elodes were studied in a temporary pond and a permanent, more productive pond in northeastern Indiana, USA. When snails from both populations were reared in each of the ponds in containers excluding predators, snails grew to be 1.3 to 2 times as large in the more productive pond, and laid 9 times as many eggs. However, field sampling data showed adults to be more abundant in the temporary pond. The only obvious difference between the two ponds was the presence of the molluscivorous central mudminnow (Umbra limi) in the permanent pond. These fish fed upon L. elodes when eggs and juvenile snails were abundant. In an experiment in the temporary pond, addition of mudminnows lowered egg and juvenile snail survival in pens where snail abundances had been increased. We suggest that vertebrate predators like the mudminnow can be significant sources of mortality for thin shelled species like L. elodes, possibly excluding them from habitats like lakes and rivers.