How do you tell the difference; they're both big & ugly fish?

Question

Whopping Fish Declared New Species

A man-sized grouper that trolls the tropical waters of the Eastern Pacific Ocean for octopuses and crabs has been identified as a new fish species after genetic tests.

Called the goliath grouper, the fish can grow to six feet (1.8 meters) in length and weigh a whopping 1,000 pounds (454 kg). Until now, scientists had grouped this species with an identical looking fish (also called the goliath grouper, or Epinephelus itajara) living in the Atlantic Ocean.

"For more than a century, ichthyologists have thought that Pacific and Atlantic goliath grouper were the same species," said lead researcher Matthew Craig of the Hawaii Institute of Marine Biology, "and the argument was settled before the widespread use of genetic techniques."

Once upon a time, about 3.5 million years ago — before the Caribbean and the Pacific were separated by present-day Panama — they were, in fact, the same species. Now, DNA tests have revealed the two populations have distinct genes, indicating they likely evolved into two separate species after their ocean homes were divided by Central America.

Scientists disagree about how to define the term "species" and what separates species from one another biologically, though some say that a species is a group that can mate with one another and produce offspring that are not sterile. However, this biological definition doesn't always hold up, for instance, with coyotes and wolves (considered separate species), which can successfully produce fertile offspring. In this study, the scientists relied on differences in the fishes' genetic codes to establish the separate grouper species.

The new Pacific species, now designated as Epinephelus quinquefasciatus, is described in a recent issue of the journal Endangered Species Research.

The Atlantic variety, E. itajara, is currently listed as critically endangered by the IUCN, or International Union for Conservation of Nature. Due to its scarcity, E. quinquefasciatus also may be considered critically endangered.

http://www.livescience.com/animals/080821-goliath-grouper.html

Answer 1

Genetic Tests

Answer 2

In general, I'm leery of allowing geneticists to determine what a species is. They can provide one sort of information, which is indeed valuable but only a single source. I would be more willing to consider the two populations separate species if the genetic evidence could be backed up by another sort of evidence, such as morphological. Sounds like a good project for an ichthyologist.

I'm not completely fossilized. I have no trouble considering the two gray tree frogs separate species because their calls differ. Kind of difficult to tell with a museum specimen though, unless you have a karyotype.

Despite what the article implied, there have been portals between the Atlantic and Pacific at different times and places, not just at Panama. Nicaragua and Colombia come to mind.