I used those because they are not behind paywalls and I'm not sure if you have access to the same studies I normally use. And yes, I have read and digested them along with many others. The majority of the first link was about how a fishes innate ability reacts to an exposure to pathogens. It then discusses how each mechanism contributes to attacking the pathogen on subsequent re-exposure. I'm not sure it gets any more relevant than that.
A more observational based study showing the concept with Cryptocaryon Irritans can be found here if you can access it.
https://www.sciencedirect.com/science/article/abs/pii/S1050464885700435
As for the second article, I feel these sections show it quite clearly.
"The complement system Fish, as other vertebrates and invertebrates, activate their immune system after recognition of pathogen-associated molecular patterns (PAMPs) by specific receptors. These receptors act as soluble forms (LPS-binding protein, pentraxins, complement, collectins) or are associated to membranes of immune cells (epithelial, phagocytic, dendritic, granulocytic). The complement system appears to be one of the central immune responses in fish."
"Here, there are some relevant differences compared with mammals. The first is that fish possess multiple active isoforms of the key activation molecule C3. Mammals have one isoform of the C3 molecule whereas fish express several functionally active C3 isoforms"