Transmission experimental design to detect genetic differences in host resistance, infectivity and tolerance. (a) Tank composition in our transmission experiment. Each of the 72 tanks comprised five artificially inoculated (shedder) fish from a single family and 20 susceptible (recipient) fish from four families. (b) Transmission experimental design in one of the trials. Each grey circle corresponds to one tank and a unique symbol-colour combination is assigned to each recipient (Ri) or shedder (Si) family in 36 tanks in one of the two trials of our experiment. The 4 shedder families (S1 to S4) were distributed across nine tanks each. Recipient families were housed in tanks such that nine recipient family combinations were created, which in turn were housed with each of four shedder families. Each recipient family was allocated in two recipient family compositions.