James E. Wetzel

Daily Increment Formation in Otoliths of the Redspotted Sunfish

Abstract To generate reliable age information for fishes, we must assess the robustness of techniques to environmental variation. We quantified daily ring deposition within the sagittal otoliths of known-age larval and juvenile redspotted sunfish Lepomis miniatus reared in ponds. We also determined how daily light : dark cycles mimicking natural conditions, reduced daylight, or constant daylight affected ring deposition in fish housed in aquaria. Additionally, we quantified how constant temperature (26°C), low daily variability in temperature (26±1°C), and high daily variability (26±2°C) affected production of daily rings. In pond-reared fish, the first increment was produced by the evening of hatch, and increment deposition occurred with 24-h periodicity through 119 d. Independent age estimates from two readers closely agreed. Photocycle and temperature variation did not affect periodicity of increment formation or the precision and accuracy of age estimates. Age and growth data can be reliably determine...

Comparison of Pond Production of Phase-III Sunshine Bass Fed 32-, 36-, and 40%-Crude-Protein Diets with Fixed Energy: Protein Ratios

Abstract We stocked phase-III sunshine bass (white bass Morone chrysops ♀ × striped bass M. saxatilis ♂) at a rate of 6,188 fingerlings/ha into twelve 0.04-ha earthen ponds supplied with continuous aeration. Three dietary treatments were randomly assigned to quadruplicate ponds. Sunshine bass were fed to apparent satiation once daily after average initial weight (mean ± SE = 214 ± 5 g) and total length (245 ± 1.6 mm) were determined. Diets were formulated to conserve the estimated digestible energy : crude protein (CP) ratio (9.3 kcal/g protein) and represented the following CP and energy values fed to fish: 32% CP (3,000 kcal/kg), 36% CP (3,360 kcal/kg), and 40% CP (3,760 kcal/kg). Harvest data suggest that nutrient density is a variable that can be manipulated to optimize production and reduce production costs. Production rates (mean ± SE) were 2,851 ± 600 kg/ha for the 32%-CP diet, 2,895 ± 341 kg/ha for the 36%-CP diet, and 2,953 ± 142 kg/ha for the 40%-CP diet; production rates were not significantly ...

MORPHOLOGICAL AND GENETIC COMPARISONS OF GOLDEN CRAYFISH, ORCONECTES LUTEUS, AND RUSTY CRAYFISH, O. RUSTICUS, WITH RANGE CORRECTIONS IN IOWA AND MINNESOTA

Abstract The distribution of the rusty crayfish, Orconectes rusticus, has been purported to include large portions of Iowa and Minnesota among many other states, whereas the golden crayfish, O. luteus, has been reported from Kansas, Arkansas, Missouri, and Illinois. Recent collections made in several river basins in Iowa and southern Minnesota and examination of museum specimens collected in Iowa revealed that many records attributed to O. rusticus are in fact O. luteus. We provide a suite of quantitative and qualitative characteristics, both morphological and genetic, that distinguish O. luteus and O. rusticus and also demonstrate that female O. luteus exhibit form alternation. Comparisons of mitochondrial 16S rRNA haplotypes among populations of O. luteus, O. rusticus, O. cf. rusticus, O. placidus, and O. virilis revealed relatively high levels of sequence divergence among taxa as well as within some taxa. We conclude that O. luteus is a native species in Iowa and southern Minnesota with introduced populations of O. rusticus occurring in both states. A more thorough survey of these states, particularly Iowa, is needed to assess the distributions of O. rusticus and O. luteus. If O. rusticus has a relatively restricted distribution in Iowa, efforts to control its anthropogenic and natural dispersal may be more effective if implemented in the near future. Our study indicates the need for more research in taxonomy, even in regions where the fauna is thought to be known well, in order for the conservation of native species and detection and management of nonindigenous species to be successful.

Distinction between Gastric Digestion and Evacuation in Black Bass Fed Piscine Prey

Abstract The terms “digestion” and “evacuation” are used interchangeably in studies of gastric processing in black basses Micropterus spp. We demonstrate that these processes are distinct and suggest that the differences may influence models involving the kinetics of gastric evacuation. Bolus (particulate matter) and residuum (bolus plus chyme (fluidized gastric contents)) sizes were used to examine gastric digestion (physical and chemical breakdown) and evacuation (passage of material from the stomach) in juvenile F1 backcross hybrid backcross black bass (largemouth bass M. salmoides × (spotted bass M. punctulatus × largemouth bass)). Thirty-five black bass (2.477–6.398 g), each fed a single female zebra danio Brachydanio rerio (wet weight = 139–619 mg), were sampled at 4.5 h postprandially. Dry-matter contents of the bolus, chyme, and residuum were related to relative prandium (meal) size and black bass wet weight. The presence of detectable chyme dry matter at all prandium sizes demonstrated that gastr...