To dissect whether pathogen-pathogen interactions (e.g., GCRV-induced modulation of A. salmonicida proliferation) depend on zfhnf4α and whether zfhnf4α has a function similar to that of gchnf4α, we leveraged zfhnf4α knockout larvae to compare pathogen dynamics across single and co-infection scenarios, while paralleling analyses of transcriptional regulation of aif, caspase 3 or caspase 9. The gene discussed is CASP3; the disease is infection.