You know what I am to for two reasons
1. You just started mud slinging
2. Im saying this from a hypothetical stand point as in it is theoretically possible and so far there's no way of proving it can't be done until it has been tried.
It simply can't be done because there is too much of a genetic disparity between the two fishes and not enough genes would match up for a viable live hybrid to be created from merging a piranha sperm with a bluegill egg or vice versa. You're talking about trying to combine the DNA from fishes that are not of the same species, genus, family, superfamily, suborder, order, and or even superorder: piranha are in the superorder Ostariophysi while bluegill are in the superorder Acanthopterygii. It's considered to be pretty lucky to get animals of different species to hybridize, let alone genus, family, etc. As such, a hybrid of this sort can not and will not ever happen via traditional fertilization, e.g. unaltered sperm merging with unaltered egg.
The zebrafish example is not a valid example for arguing for the possibility of a piranha/bluegill hybrid because it's not an example of a hybrid, rather it is an example of gene addition: a single gene from the jellyfish genome (specifically the gene for glowing, GFP) was inserted in a zebrafish embryo and the gene was integrated into the genome of the zebrafish. The zebrafish embryo was already formed via traditional fertilization and was 100% zebrafish prior to the addition of the gene.
So in short, Water was correct to say that such a hybrid was and is still impossible, so there's really no point in thinking that it is hypothetically possible. I'm not seeing any "mudslinging" here either; Water was just pointing out the facts. Personally, I could easily go on in much more detail all day about how this hybrid wouldn't work, but I have better things to do which brings me to my final question: Are you just trolling this one, Tropicalfish34?