Answer:
Control experiment
Step-by-step explanation:
This a treatment of no change in the experiment whereby all variables ( usually the effects of the independent variable on the dependent variable) are well known. The control experiment is used to compare the outcomes with those of other treatments so as to verify and validate the experiment ad its results.
In this experimenter, placing another equal amount of fertilised fish eggs, from the same batch, in the water of salinity levels equal to that it would find in its normal environment, would be the control experiment.