Biology 313
Ecotoxicology lab
Hypothesis: Road salt (NaCl) is considered an aquatic pollutant. The current aquatic
standard of 230 mg/L chloride is not toxic to fish
You will assess fish for responses to increasing concentrations of NaCl over an
approximate one month exposure.
Note: The fish you will be using (cichlids) are not native to Minnesota. Ideally you would
use test organisms from your habitat of interest.
In this experimental design there are six exposure levels (no salt added=control, 10 mg/L
Cl (as NaCl), 23 mg/L Cl (as NaCl), 100 mg/L Cl (as NaCl), 230 mg/L (as NaCl) Cl, 500
mg/L (as NaCl)). For each treatment there are 6 independent replicated samples (tanks).
Each tank contains 2 cichlids and Lemna aquatic plants.
Each tank is numbered with a piece of colored tape. The following treatments are
randomly assigned: Control (6 tanks), 10 mg/L Cl (6 tanks), 23 mg/L Cl (6 tanks), 100
mg/L Cl (6 tanks) , 230 mg/L Cl (6 tanks), 500 mg/L Cl (6 tanks).
The specific concentration is not provided on the tanks so that all assessments are
conducted without bias to the treatment.
Establish a group of three to four students and select two endpoints for the fish.
Examples
-appetite assessment (time the response when food is added to the tank )
-opercular movement (number of times gills are observed to open and close/minute)
-swimming behavior
-mobility (quantify the number of times a fish passes a marker in a specified time)
-any other endpoint you wish to use approved by the instructor
Take initial readings at the beginning of the exposure period. Once a week measure
water temperature, pH and conductivity. Record the means and standard deviations for
each treatment.
-Take notes and record the data on your endpoints
-record any additional observations that may indicate a toxic effect
-remove and count mortalities if and when they occur. Record this information on the
data sheet (posted).