What is a "big" fish?
Exactly what constitutes a "big fish" in aquarium terms is open to debate, and not as straight-forward to define as it might seem.
The length of a fish alone does not define its size (e.g. some fish are much deeper-bodied than others), nor its suitability for a particular aquarium size.
This is one reason why the Big Fish Campaign is not attempting to define a "cut-off size" for fish that are not recommended for sale or purchase - there are simply too many variables to make this a practical or workable option.
However, it is clear that fish above a certain adult size are unlikely to be suitable for even very large home aquaria - realistically most fish that will attain 75cm (30") or more can only be accomodated in specially built ponds or giant aquaria such as those found in public aquarium facilities.
It would also be recommended that any fish that can attain 30cm (12") or more should always be labelled with their potential adult size by retailers.
Big Fish need Big Homes!