DOI: 10.5061/dryad.v6wwpzh86
title: Interactive effects of temperature and food ration on growth and mercury concentration in eastern brook trout

description: Warming temperatures predicted under global climate change will alter the
 dynamics of secondary production and trace element accumulation and may
 interact with environmental factors such as food resource availability to
 influence growth and bioaccumulation. We conducted laboratory experiments
 to assess the role of temperature and food ration on Brook Trout growth
 and mercury (Hg) concentration. Across a range of temperatures (16 –
 24°C), Brook Trout growth rate decreased, and Hg concentration increased
 with temperature. We observed the lowest Hg concentrations in fish under
 the low temperature (15°C), high ration treatment, and the highest
 concentrations in the high temperature (22°C), zero ration treatment. The
 relative growth rank of individual fish was a significant predictor of Hg
 concentration, with fast-growing individuals having lower Hg. Based on
 structural equation modelling (SEM), the strongest relationship between
 Brook Trout Hg and the temperature/ration treatments was through an
 indirect pathway mediated by Brook Trout growth rate. Our results provide
 support for a link between warming temperatures, growth, and
 bioaccumulation rates in upland stream food webs, with implications for
 wildlife and human health.
description: # Interactive effects of temperature and food ration on growth and mercury
 concentration in eastern brook trout Dataset DOI:
 [10.5061/dryad.v6wwpzh86](10.5061/dryad.v6wwpzh86) ## Description of the
 data and file structure This dataset and analysis evaluate the brook trout
 mercury (Hg) experiments presented by Rutledge et al. 2025. Interactive
 Effects of Temperature and Food Ration on Specific Growth and Mercury
 Concentration in Eastern Brook Trout. *CJFAS*. The focus of the laboratory
 experiment used manipulations of water temperature and food ration
 treatments to see how Hg concentration changed in brook trout. ### Files
 and variables #### File: Rutledge_etal_2025CJFAS_Rproj.zip
 **Description:**  This zipfile contains an RStudio R Project directory. At
 the top directory level, there are three main files. 1. The first is the R
 Project file named "Rutledge_etal_2025CJFAS_Rproj.Rproj". Open
 this project file within RStudio. 2. The second and third files are named
 similarly but represent .Rmd and .html file types. The .Rmd file named
 "*bkt_hg_temp_ration_experiment_analysis.Rmd*" contains the R
 code chunks for data import, manipulation, statistical analysis, and
 figure generation for the paper. The HTML version of the file
 ("*bkt_hg_temp_ration_experiment_analysis.html*") is a knitted
 version of the .Rmd file for easy viewing of the analysis code. These
 files contain sections for each of the two experiments in the paper.
 Additionally, for each experimental data set, there is a metadata
 dictionary for the imported data sets. The top directory also contains 5
 subdirectories. These are: 1. **data** - contains four data files that
 represent the raw data produced by the two experiments. each experiment
 has an .RDS file to easily import the data into R and a corresponding .csv
 file that presents the same data in a more shareable format for most
 operating system spreadsheet software options. 1. ***Experiment One data
 files*** contain the following variables: 1. ***PIT:*** pit tag identifier
 for each individual fish. 2. ***tank:*** the experimental tank the
 individual fish was within for the duration of the experiment. 3.
 ***Hg:*** brook trout mercury muscle tissue concentration in ng per g of
 dry weight. 4. ***temperature:*** the mean temperature of the water
 measured in the tank across the duration of the study in degrees Celsius.
 5. ***tempfac:*** classification for temperature treatments as a factor
 (16, 18, 20, 22, 24 degrees C). 6. ***tot_tank_consumption:*** the total
 mass (g) of food fed to a treatment across the duration of the experiment.
 7. ***day00massg:*** mass (g) of individual fish at the start of the
 experiment 8. ***day24massg:*** mass (g) of individual fish at the end of
 the experiment 9. ***conv_eff:*** tank-based conversion efficiency for
 fish (unitless value) 10. ***growth_spe:*** specific growth rate for
 individual brook trout calculated as the
 ((ln(day24massg)-ln(day00massg))/24days)*100. 
 
 2. ***Experiment Two data files*** contain the following variables: 1.
 ***PIT:*** pit tag identifier for each individual fish. 2. ***tank:*** the
 experimental tank the individual fish was within for the duration of the
 experiment. 3. ***Hg:*** brook trout mercury muscle tissue concentration
 in ng per g of dry weight. 4. ***temperature:*** the mean temperature
 (degrees C) of the water measured in the tank across the duration of the
 study. 5. ***tempfac:*** classification for temperature treatments as a
 factor (16, 18, 20, 22, 24 degrees C). 6. ***ration:*** mass (g) of food
 fed to an individual fish as an average value for a given tank. 7.
 ***rationfac:*** classification for ration treatments as a factor
 ("zero", "low", or "high"). 8.
 ***day00massg:*** mass (g) of individual fish at the start of the
 experiment 9. ***day30massg:*** mass (g) of individual fish at the end of
 the experiment 10. ***growth_spe:*** specific growth rate for individual
 brook trout calculated as: ((ln(day30massg)-ln(day00massg))/30days)*100.
 11. ***growth_abs:*** absolute growth change for individual brook trout
 calculated as: day30massg-day00massg. 12. \***conv_eff: ***tank-based
 conversion efficiency for fish (unitless value) 13.
 ***growth_abs_tnk_rnk:*** absolute growth difference rank for individual
 fish within a given tank. Values range from 1-10, with fish ranked near 1
 having larger absolute growth differences between the start and end of the
 experiment, and fish ranked closer to 10 having smaller absolute growth
 differences. 14. ***VARIABLE_s:*** named variable (in place of
 "*VARIABLE*") scaled to a mean of 0 and standard deviation of 1,
 appended with a "_s" to distinguish from the raw units column.  
 
 2. **figs** - the figures generated in the paper will be populated here
 as both PNG and EPS file types if this R script is run. 3. **fnx** -
 contains a function .R file written for fitting and visualizing piecewise
 regression models specific to this data set. This is sourced in the .Rmd
 file. 4. **sessionInfo** - contains one text file with the
 "sessionInfo()" output for the R project. This file lists the R
 packages and their version numbers, as well as the R version and computer
 operating system used when this data package was published. 5. **tables**
 - contains a .csv file with the data supporting Table 1 from the paper. ##
 Code/software This data package used R (v4.5.0) and RStudio (v2024.12.1)
 to complete the data analysis and visualization. Additionally, the R
 Project session information is populated in the data product as noted
 above with each R package and its version number to help future users
 maintain R package versions for transferability and compatibility of the
 data analysis when attempting to rerun the analyses with the associated
 data set. ## Access information Data were all derived from experimental
 laboratory analyses and are not located anywhere else for access.