Prey preference for Asian carp and soft plastic lure ingestion by largemouth bass

Invasive bighead (Hypophthalmichthys nobilis) and silver carp (Hypophthalmichthys molitrix) have become established throughout much of the Mississippi River basin. In many areas, these two species comprise a significant proportion of the fish biomass. Despite their prevalence and potential for negative environmental impacts, to date, there has been no assessment of vulnerability to predation of Asian carp compared to native species. We sought to examine largemouth bass (Micropterus salmoides) predation on juvenile bighead and silver carp in relation to common native prey species. Prey species selection experiments in 2-m pools showed number of prey captures was highest for bighead carp followed by gizzard shad with lower capture rates for bluegill, golden shiner, and silver carp. Observations of prey and predator behavior were quantified in a 720-L aquarium and variation in anti-predator behavior explained relative differences in vulnerability to predation. Differences in vulnerability to predation may explain the greater invasion success of silver carp. Similar or higher vulnerability to predation of Asian carp compared to common native prey suggests that they may serve as viable prey for native predators mitigating the potential negative impacts on the native prey community. Soft plastic fishing lures (SPLs) have recently gained attention as a potential source of pollution in aquatic systems. A number of anecdotal reports have suggested that discarded SPLs are being ingested by wild fish and causing health problems including mortality. Few studies have been conducted concerning the effects of SPLs on fish. We designed a laboratory study to determine the effects of ingestion of three different shapes and two different materials of SPLs on consumption by largemouth bass. No effects on consumption were observed except on the first day after SPL ingestion. In three trials with 30 fish, all largemouth bass were ultimately capable of expelling the lures from their bodies. Field data were also utilized to determine the occurrence of SPL ingestion by largemouth bass in the wild. In two Illinois lakes, occurrence rates of SPL ingestion were < 1%. Bass sampled with SPLs in their stomach did not have significantly different body condition from fish that had not ingested SPLs. We conclude that discarded SPLs do not pose a significant threat to the health of largemouth bass. Nevertheless, we encourage efforts to responsibly dispose of SPLs in order to prevent pollution and any possible undiscovered consequences of their presence in the environment

Evaluation of rate law approximations in bottom-up kinetic models of metabolism.

BackgroundThe mechanistic description of enzyme kinetics in a dynamic model of metabolism requires specifying the numerical values of a large number of kinetic parameters. The parameterization challenge is often addressed through the use of simplifying approximations to form reaction rate laws with reduced numbers of parameters. Whether such simplified models can reproduce dynamic characteristics of the full system is an important question.ResultsIn this work, we compared the local transient response properties of dynamic models constructed using rate laws with varying levels of approximation. These approximate rate laws were: 1) a Michaelis-Menten rate law with measured enzyme parameters, 2) a Michaelis-Menten rate law with approximated parameters, using the convenience kinetics convention, 3) a thermodynamic rate law resulting from a metabolite saturation assumption, and 4) a pure chemical reaction mass action rate law that removes the role of the enzyme from the reaction kinetics. We utilized in vivo data for the human red blood cell to compare the effect of rate law choices against the backdrop of physiological flux and concentration differences. We found that the Michaelis-Menten rate law with measured enzyme parameters yields an excellent approximation of the full system dynamics, while other assumptions cause greater discrepancies in system dynamic behavior. However, iteratively replacing mechanistic rate laws with approximations resulted in a model that retains a high correlation with the true model behavior. Investigating this consistency, we determined that the order of magnitude differences among fluxes and concentrations in the network were greatly influential on the network dynamics. We further identified reaction features such as thermodynamic reversibility, high substrate concentration, and lack of allosteric regulation, which make certain reactions more suitable for rate law approximations.ConclusionsOverall, our work generally supports the use of approximate rate laws when building large scale kinetic models, due to the key role that physiologically meaningful flux and concentration ranges play in determining network dynamics. However, we also showed that detailed mechanistic models show a clear benefit in prediction accuracy when data is available. The work here should help to provide guidance to future kinetic modeling efforts on the choice of rate law and parameterization approaches