Laboratory Evaluation of Two Bioenergetics Models for Brown Trout

Laboratory growth and food consumption data for two size classes of brown trout Salmo trutta that experienced three distinct feeding regimes at two temperatures were used to evaluate the abilities of two bioenergetics models to predict fish growth. Accuracy of cumulative consumption predictions was also tested for one of the models. Model errors for predicting relative growth rate of individual fish were regressed on observed mean daily consumption rate to assess whether consumption-dependent prediction error commonly observed in bioenergetics models for other fish species was exhibited by the two brown trout bioenergetics models. Both models yielded unbiased estimates of brown trout growth that were within 1-12% of observed values across the range of fish sizes, water temperatures, and ration levels tested. Bonferroni joint 95% confidence intervals for the slopes and intercepts of regressions of predicted final weight on observed final weight included a slope of 1 and a y-intercept of 0 for both models. No significant inter-model differences in percent error for predicting final weight of fish in feeding trials were observed. Predicted cumulative consumption values were within 8-15% of corresponding observed values. Neither model exhibited significant consumption-dependent error for predicting brown trout growth, in contrast to results of several previous laboratory evaluations of bioenergetics models for other fish species. Absence of consumption-dependent error in the two brown trout models may be due to incorporation of feeding rate-dependence of egestion and excretion in these models and that egestion and excretion parameters were not borrowed from other species. Results of this evaluation corroborate the utility of these bioenergetics models for predicting growth and consumption for brown trout under the range of fish sizes, water temperatures, and ration levels tested

Changes to water quality and sediment phosphorus forms in a shallow, eutrophic lake after removal of common carp (Cyprinus carpio)

Pickerel Lake (Minnesota, USA) is a shallow, polymictic lake that has had eutrophication problems for decades. Although excess nutrient loading has been a problem in the past, the dominance of common carp (Cyprinus carpio) was considered to be a substantial factor driving and sustaining eutrophic conditions. To remove carp and restore the fish community, the lake was treated with rotenone in late 2009 and then restocked with native species. All water quality variables improved after carp removal, with mean values (May-Sep) for chlorophyll a, total phosphorus, and turbidity decreasing by 80% to 93% and Secchi disk transparency increasing nearly 600% when comparing means of pre- to post-treatment years. Macrophyte coverage also improved, from means of 4.6% before treatment to 90% after treatment, indicating a shift from an algal- to a macrophyte-dominated system. Sediment phosphorus (P) storage increased significantly after carp removal as well, with labile (releasable) forms of P increasing in the upper 10 cm of sediment in all cores (n = 7). The decrease in water column P equaled the increase in labile sediment P forms after treatment, indicating carp were a key driver of P transport from sediment to water. The results of this study indicate that an ecological (i.e., both abiotic and biotic) approach is needed when managing eutrophic lakes because management of nutrients alone will not likely be adequate to restore water quality in systems dominated by carp or other large benthic feeding fish

Improvement of Bioenergetics Model Predictions for Fish Undergoing Compensatory Growth

A previous evaluation of a bioenergetics model applied to juvenile hybrid sunfish (F1 hybrid of female green sunfish Lepomis cyanellus × male bluegill L. macrochirus) undergoing compensatory growth (CG) indicated that the model substantially overestimated growth and underestimated cumulative consumption. This result suggested that fish bioenergetics models might not adequately account for physiological shifts that occur during CG. However, we demonstrate that application of a recently developed procedure for correcting consumption- and growth-rate-dependent systematic errors common among bioenergetics models negates much of the predictive error that had been attributed to the physiological complexities of CG. Correction equations for estimating the model-relative growth rate error (predicted less observed; g · g−1 · d−1) from the observed mean daily consumption rate (g · g−1 · d−1) and the consumption rate error (predicted less observed; g · g−1 · d−1) from the observed relative growth rate (g · g−1 · d−1) were derived by applying linear regression analysis to data from individual hybrid sunfish not undergoing CG. These independently generated correction equations significantly improved model predictions of growth and cumulative consumption for three groups of fish undergoing CG at one temperature near their growth optimum. The findings indicate that the high consumption and growth rates characteristic of fish undergoing CG merely amplify the consumption- and growth-rate-dependent errors inherent in bioenergetics models and that model predictions for fish undergoing CG can be significantly improved through application of the correction procedure

Variation in native micro-predator abundance explains recruitment of a mobile invasive fish, the common carp, in a naturally unstable environment

Why certain species of fish become invasive is poorly understood and a key obstacle to restoring many of the world’s ecosystems. In this study we tested whether variation in biotic resistance exerted by native predators might explain the reproductive success of the common carp, a large and fecund invasive species that typically spawns in outlying and unstable shallow habitat. An initial three-year study of the relative abundance of youngof- year (YOY) carp in interconnected lakes in the Upper Mississippi River Basin discovered that YOY carp are only found in shallow waters that experience winter hypoxia (winterkill) and have low densities of the native egg-predators that otherwise dominate these locales. A follow-up experiment tested if native fish predation on carp eggs could explain this distribution. It found that while carp eggs survived in winterkill lakes, they only survived in non-winterkill lakes when protected by a mesh that excluded fish. Large numbers of carp eggs were found in the stomachs of native fish inhabiting lakes that did not winterkill. We conclude that common carp, and likely many other highly mobile and fecund invasive fish, have evolved life histories to avoid egg predators and can become invasive when they are absent

Widespread Consumption-dependent Systematic Error in Fish Bioenergetics Models and its Implications

Data from laboratory evaluations of seven fish bioenergetics models (BEMs) were used to investigate possible associations between BEM prediction error in relative growth rate (RGRerror) and levels of model input variables: mean daily food-consumption rate and fish body weight. Correlation between RGRerror and fish body weight was found in three BEMs applied under submaintenance feeding conditions. A strong correlation between RGRerror and mean daily consumption level was observed in all models over full consumption ranges; consumption level explained 70%–96% of variation in RGRerror. All BEMs underestimated (by 2- to 5-fold) growth at lower consumption levels and overestimated (by 2- to 3-fold) growth at higher consumption levels. RGRerror values associated with higher consumption levels were greater (up to 22 cal·g–1·day–1) than those at lower consumption levels (up to 10 cal·g–1·day–1). Correlation between consumption rate and RGRerror in all seven models indicates widespread systematic error among BEMs that likely arises from deficiencies in consumption-dependent model parameters. Results indicate that many BEMs are substantially inaccurate when predicting fish growth from higher feeding rates or estimating consumption from higher growth rates, even when higher consumption levels or growth episodes are of short duration. Findings obtained under submaintenance feeding conditions indicate that additional body-weight- and consumption-dependent terms should be added to BEM subequations for routine metabolism to account for metabolic reduction

Data from: Tests in a semi-natural environment suggest that bait and switch strategy could be used to control invasive Common Carp

There are four files: 1) PIT_tagged_FISH contains unique PIT tag for every fish, plus length, species, pond, date of mortality, 2) Raw_detections contains all fish detected during study, 3) Summarized_mortalities contains summaries of the fish mortalities by pond and species before and after experimental treatment, and 4) R_code contains a summary of and code for the R analysis used.Common Carp (Cyprinus carpio Linnaeus, 1758), is a highly invasive species that has had profound effects on biodiversity and ecosystem services. Many Carp management methods have been applied including physical removal, pesticide treatments of whole lakes, and water drawdowns. Herein, we tested key elements of a potential “bait and switch” approach in which corn could be used to induce feeding aggregations of Carp and then switched for corn pellets with a pesticide Antimycin-A (ANT-A) to selectively target the Carp. First, laboratory experiments were used to determine if addition of lethal concentrations of ANT-A to corn pellets deterred Carp from eating corn-based food pellets. Second, a pond experiment tested if a corn-based bait containing ANT-A functioned as a species-specific Carp management tool in a semi-natural environment with three common native fishes: White Sucker (Catostomus commersonii Lacepède, 1803), Yellow Perch (Perca flavescens, Mitchill, 1814), and Bluegill (Lepomis macrochirus Rafinesque, 1819). The use of baited sites by Carp and native species was monitored using passive integrated transponder (PIT) tags. Mortality of each species and presence of corn in their digestive tracts was also monitored.This project was funded by the Environment and Natural Resources Trust Fund (ENRTF) in association with the Minnesota Aquatic Invasive Species Research Center at the University of Minnesota

Simultaneous Identification and Correction of Systematic Error in Bioenergetics Models: Demonstration with a White Crappie (\u3ci\u3ePomoxis annularis\u3c/i\u3e) Model

Recent evidence indicates that important systematic error exists in many fish bioenergetics models (BEMs). An approach for identifying and correcting this error is demonstrated with a white crappie (Pomoxis annularis) BEM. Model-predicted trajectories of growth and cumulative consumption for 39 individual white crappie obtained from six 60-day laboratory experiments diverged from observed values by up to 42.5% and 227%, respectively, indicating systematic error in the BEM. To evaluate correlates of the systematic error, model prediction errors were regressed against three major input/output variables of BEMs that were covered by the laboratory experiments: fish body weight (80–341 g), temperature (23–30 °C), and consumption level (0.5%–6.2% daily). Consumption level explained \u3e80% of the prediction error for growth and consumption. Two multiple regression equations containing body weight, temperature, and consumption variables were developed to estimate growth prediction error (R2 = 0.96) and consumption prediction error (R2 = 0.86), and incorporated into the white crappie BEM to correct its predictions. Cross-validation indicated that growth and consumption prediction error was reduced 2- to 4-fold by correction. Given recent evidence of widespread systematic error and increasing application rates of BEMs, the efficient error-identification and -correction approach described appears broadly applicable and timely

The Relationship between the Distribution of Common Carp and Their Environmental DNA in a Small Lake

<div><p>Although environmental DNA (eDNA) has been used to infer the presence of rare aquatic species, many facets of this technique remain unresolved. In particular, the relationship between eDNA and fish distribution is not known. We examined the relationship between the distribution of fish and their eDNA (detection rate and concentration) in a lake. A quantitative PCR (qPCR) assay for a region within the cytochrome <i>b</i> gene of the common carp (<i>Cyprinus carpio</i> or ‘carp’), an ubiquitous invasive fish, was developed and used to measure eDNA in Lake Staring (MN, USA), in which both the density of carp and their distribution have been closely monitored for several years. Surface water, sub-surface water, and sediment were sampled from 22 locations in the lake, including areas frequently used by carp. In water, areas of high carp use had a higher rate of detection and concentration of eDNA, but there was no effect of fish use on sediment eDNA. The detection rate and concentration of eDNA in surface and sub-surface water were not significantly different (p≥0.5), indicating that eDNA did not accumulate in surface water. The detection rate followed the trend: high-use water > low-use water > sediment. The concentration of eDNA in sediment samples that were above the limit of detection were several orders of magnitude greater than water on a per mass basis, but a poor limit of detection led to low detection rates. The patchy distribution of eDNA in the water of our study lake suggests that the mechanisms that remove eDNA from the water column, such as decay and sedimentation, are rapid. Taken together, these results indicate that effective eDNA sampling methods should be informed by fish distribution, as eDNA concentration was shown to vary dramatically between samples taken less than 100 m apart.</p></div

Results of a 3-way ANOVA for CarpCyt<i>b</i> marker in water samples.

<p>Results of a 3-way ANOVA for CarpCyt<i>b</i> marker in water samples.</p

Carp use and distribution of eDNA in Lake Staring.

<p>Panel A shows locations of radiotagged carp and high- and low-use areas. Density categories represent the average number of locations of radiotagged carp/km². The high- and low-use area cut-off value of 800 radiotagged carp/km² corresponded to approximately 1,248 carp/ha. Panels B–D show the pattern of eDNA detection and concentration in surface water (B), sub-surface water (C), and sediment (D). All figures have the same scale. The symbol legend in the upper right refers to panel A, whereas lower right refers to panels B–D.</p