If a disease in a tank would kill fish if introduced to the wild, it would affect the fish I bring home the same way. The fish you decide to keep aren't magically immune to a disease in a new tank so their buddies will be able to survive it if they can.
interesting. so you're saying...
no one or everyone dies from chickenpox.
Researchers from the CDC looked at data from 1990 to 2007.
"Every kid did get chickenpox and, in the pre-vaccine era, there were 3-4 million cases a year," Seward said. "What people may not have realized, every year, about 105 people died of chickenpox. About half of those were children and about 11,000-12,000 were hospitalized with severe complications. We started preventing the disease to really prevent those very serious complications."
so thousands get chicken pox, but only 105 people die each year...
all dogs or no dogs die from canine distemper...
Canine distemper is a viral disease that affects dogs worldwide. The disease is most common in young, unvaccinated dogs. Initially, fever and ocular and nasal discharge will be seen, but this will progress to include clinical signs involving the gastrointestinal tract, respiratory tract and central nervous system. The mortality rate can reach 50 percent.
again, your theory doesn't hold true.
or if you want to get technical about it-
Genetically similar VHSV isolates are differentially virulent in olive flounder Paralichthys olivaceus.
Two viral hemorrhagic septicemia virus (VHSV) isolates, VHSV-KR-CJA and VHSV-KR-YGH, were isolated from viral hemorrhagic septicemia disease outbreaks in flounder farms in South Korea. The VHSV-KR-CJA isolate was isolated from a flounder farm with high mortality (80%), while the VHSV-KR-YGH isolate was isolated from a flounder farm with low mortality (15%), suggesting that these isolates differ in virulence. The virulence of these isolates was evaluated in juvenile flounder via intraperitoneal injection. Consistent with their virulence in the field, mortality data revealed that the VHSV-KR-CJA isolate was highly pathogenic (cumulative mortality of 80%), while the VHSV-KR-YGH isolate was less pathogenic in flounder (cumulative mortality of 20%). To characterize the genotypes of these viruses, the full open reading frames (ORFs) encoding nucleoprotein N, phosphoprotein P, matrix protein M, glycoprotein G, nonstructural viral protein NV, and polymerase L of these viruses were sequenced and analyzed. Sequence analysis revealed that both isolates are genetically very similar (identical amino acid sequences for P, M, NV, and L and >99.7 and 99.8% amino acid sequence identity for N and G, respectively). Phylogenetic analysis indicated that both of these viruses belong to the Genotype IVa group, suggesting that they originated from a common ancestral virus. The low pathogenicity VHSV strain may potentially evolve to become a more pathogenic strain through only a few nucleotide substitutions. Further functional analyses of mutations in VHSV genes are necessary to identify factors that determine VHSV pathogenicity in flounder.
and how about cross contamination? there are plenty of species that can carry disease and transfer to another species, reptiles commonly transfer salmonella to humans, fleas transfer bubonic plague from rodents to humans.
who's to say that fish you just released isn't carrying tuberculosis, dropsey, vibrosis, or fin rot bacteria that is able, or has mutated enough to infect another fish, bird, or reptile when eaten. there's plenty of nasties that live in an aquarium and don't necessarily manage to infect the fish but still are hitching a ride on their skin, or in their poop.
