Related FAQs: Biological Classification, Marine Microbes, Marine Virus, Marine Bacteria, Marine Funguses, Marine Protozoans, Marine Plankton,  Live Rock, Related Articles: Marine Virology, Marine Bacteria, Marine Mycology, Marine Protozoans, Invertebrates, Marine Plankton, Phytoplankton, Marine Macro-Algae What's In A Name? Ever Wondered Why They Keep Changing the Latin Name of Your Favorite Fish?

By Neale Monks

One of the things that characterise experienced aquarists is their use of scientific, or Latin, names. Aquarists that become keen on groups of fishes such as cichlids, catfish, and killifish quickly find that relying on common names soon becomes untenable, as the overwhelming majority of those kinds of fish don't have common names. Even among the more familiar tetras and livebearers, there are far more species only known by their scientific names.

Besides being the only available names for many types of fish, scientific names also provide a degree of clarity lacking even if you stick with English language common names, let alone those in other languages. British aquarists familiar with black widow tetras and glassfish might be surprised to learn that in America those species are often called petticoat tetras and jewel tetras instead! Common names change over time, too; did you know that during the 1970s and 80s, the popular brackish water mono, Monodactylus argenteus, was widely referred to as the Malayan angel? Moreover, does anyone refer to guppies and discus as millionsfish or pompadours anymore?

However, scientific names are more than just a convenient way to establish the identity of a fish, they also reveal information about the relationship that fish has to all the others. Once you understand that all those animals that we refer to as fish actually comprise a number of distinct groups, then it becomes much easier to make predictions about the maintenance and behaviour of a mystery fish, even if that fish has never been kept in captivity before! While not a sure-fire replacement for a good encyclopaedia of tropical fish or a subscription to PFK, a slight education in fish taxonomy will stand you in good stead next time you go shopping for oddball tropical fish.

 

Phylogeny 101

While fish taxonomy has often been likened to stamp collecting ' each scientist trying to outdo the other by naming new species and devising new families ' at its best, this branch of science serves to make clear how all the thousands of different fishes are related to one another. Some scientists examine the skeletons of fish closely, some study the genes, and others pore over the fossil record. All are carefully looking for clues to the phylogeny of the fishes.

Phylogeny is best considered to be the like a family tree, while scientific names are rather more like our own family names. If you think about it, while our family names sometimes tell others about who we are biologically related to, this isn't always the case. Married women take on the names of people they're not related to by blood, as do children who have been adopted. So just because angelfish, discus, Kribensis, and orange chromides are all cichlids ' members of the family Cichlidae ' doesn't mean that they are all equally closely related to one another. In this example, while angels and discus actually are close relatives, they are only distantly related to the krib and to the orange Chromide even more distantly. If you look at the diagram here, you can see a family tree containing these four cichlids, with the discus and angelfish close together, the krib a bit further out, and the orange Chromide further out again.

PICTURE 1

This sort of diagram, called a cladogram, is at the heart of the way modern taxonomy describes the relationships between fishes. As more data is collected about the morphology and genes of these fish, the trees become ever more refined, and to keep pace with these changes is one of the reasons cichlid-keepers in particular are constantly bombarded with new Latin names. The branch with the discus and angelfish on, for example, is known as the subfamily Cichlasomatinae, and it includes, among other species, the popular festive cichlid, Mesonauta festivum. Stepping down the tree, the branch with the Kribensis is that of the subfamily Pseudocrenilabrinae, and includes all the other African cichlids except for those from Madagascar.

The orange Chromide, together with two other Chromide species from Asia and the Madagascan cichlids of the genus Paretroplus, form a branch all their own, the subfamily Etroplinae. These cichlids can justifiably be called the most primitive of all living cichlids, and closely resemble the marine ancestors of the cichlids in morphology and behaviour. The brackish water habitats favoured by the Asian chromides in particular is a reminder that not quite all cichlids have completely made the break with sea. In some sense, cichlids are, at heart, marine fish, and many species are remarkably tolerant of brackish water; a few thrive and even breed in salt water if they must.

 

This month's new name is

Once you have a cladogram with lots of species attached to it, you can work out all sorts of subtle relationships. Consider the Central American cichlid genus Cichlasoma, a group that includes such popular aquarium fish as the Firemouth cichlid, Cichlasoma meeki, and the convict, Cichlasoma nigrofasciatus. Ever wondered why all the fish-geeks go around giving these otherwise familiar fish such unattractive names as Thorichthys and Archocentrus? All will be revealed!

Consider the traditional approach, where convicts, Firemouths, and all the other Cichlasoma species are bundled together. Certainly, they have much in common, but are they all as closely related to one another, as this would suggest? Did they all evolve, simultaneously, from a single common ancestor? Of course not ' across millions of years new species of Cichlasoma appeared in different places and subject to different environmental pressures. Phylogeny reveals the texture of this radiation of species, marking out the ones that are closely related, and the ones that are more distantly related.

PICTURE 2

The diagram above shows the difference between the traditional and phylogenetic approaches. According to one recent paper I looked at, convicts and red devils, Cichlasoma labiatum, are more closely related to one another than either is to Cichlasoma salvini. Likewise, Firemouths and Texas cichlids, Cichlasoma carpinte, are closely related to one another, and more so than either is to Cichlasoma festae. As scientists learn more about the phylogeny of these cichlids, they give each clump of species its own generic or subgeneric name, from whence come such mouthfuls as Amphilophus, Thorichthys, and Herichthys.

One nice thing about these sometimes horrible names is they don't seem to last for long ' a year or two after one paper is published, another scientist comes along with a totally different scheme and a whole slew of new or redefined names. Aquarists needn't feel guilty about sticking with old-fashioned catchall names like Cichlasoma and Haplochromis in the meantime!

 

Hazardous hybrids

Because phylogeny shows us which species are most closely related, it also gives us fair warning as to which species might hybridise in aquaria. Besides cichlids, there are numerous Corydoras and Loricariid catfish, killifish, halfbeaks, and livebearers that belong to groups of very closely related species. Taking halfbeaks as an example, all the large halfbeaks of the genus Nomorhamphus are collected from the same Indonesian island, Sulawesi. Exporters do not make much effort to distinguish the different species, and as a result, it is not only possible but actually quite probable that a single batch of Celebes halfbeaks will contain not just the standard-issue Nomorhamphus liemi but also Nomorhamphus ebrardtii, Nomorhamphus ravnaki and others. Anyone trying to breed these fishes will therefore need to be very careful to separate out the difference species to avoid hybridisation. Hybrid halfbeaks exhibit reduced fertility and a higher risk of morphological deformities such as curved spines.

The problem is that the more closely fish are related, the more likely it is that they will speak the same language when it comes to breeding time. Hybrids are usually sterile, so if one species mates with another, it has effectively wasted energy and resources without doing anything to send its genes onto subsequent generations. Fish therefore avoid hybridizing by using a mixture of colour patterns and behaviour to ensure that only genetically compatible individuals will attempt to mate, guaranteeing that their offspring will be fertile and so able to carry the genes of the parents on down the generations. However, if species are very closely related, not only are they potentially genetically compatible, but their breeding colours and mating rituals are sufficiently similar that the normal blocks to hybridisation just don't exist. The result is fertile offspring mixing characteristics of both the species they are descended from, and so fully representative of neither.

Failure to prevent hybridisation has unquestionably messed up the bloodlines of many popular aquarium fish. The infamous mixed African cichlids sold in many tropical fish stores is a testament to how willingly Pseudotropheus zebra, among others, will hybridise with closely related species. Similarly, few commercially available Endler's guppies have reliable pedigrees, most of them being the result of cross male Endler's with standard issue female guppies. Nice fish, to be sure, but aren't Endler's guppies in any meaningful sense. More seriously, hybridisation is a major threat to the efforts of aquarists working hard to ensure the survival of species that are rare or extinct in the wild, as is the case with some livebearers and cichlids in particular.

 

Par for the genus

The above expression is one of my favourite bits of biological slang. It is taken from the sport of golf, where par for the course refers to the average number of strokes required to complete all eighteen holes on a golf course; in other words, something expected or typical. When a biologist says something is par for the genus, they mean that while they might not know this particular species, they know its close relatives, and what they've seen of the new species doesn't surprise them much. Likewise, an aquarist observing a new species of Tetraodon puffer nipping fins might say much the same thing.

Species within a genus tend to share many characteristics. The problem with the big, old-fashioned genera was that they contained so many species that establishing these commonalities can be difficult. Modern phylogeny refines these genera, making them smaller and more tightly defined.

Here's a good example: the genus Chanda. Not so long ago, this genus included a over a dozen species in size from 4-30 cm and spanning a range of habitats including blackwater streams and shallow seas, but mostly brackish water estuaries. The popular Indian glassfish, Chanda ranga, were but one of those species, and by comparison with its relatives, was assumed a brackish water fish. The situation is very different now, with many of the species formerly included in the genus Chanda now referred to three new genera, Ambassis, Parambassis, and Pseudambassis. The species kept as aquarium fish are now revealed as members of the genus Parambassis, all of which are fresh, not brackish water, fish.

In this example, the intellectual pursuits of the scientists have yielded useful information for the aquarist interested in keeping an otherwise little-understood group of fishes. If they understand the phylogeny of certain groups of fish, advanced aquarists are in a good position to predict the requirements of new species as they turn up. Each year, new species of Corydoras catfish, Stiphodon and Rhinogobius gobies, and Apistogramma cichlids turn up, for which little concrete information is available. By referring to their closest relatives, aquarists are in a good position to guess the correct water conditions these fish need, to provide them with appropriate food, and to facilitate successful breeding.

 

Use them or lose them?

The fact that Latin names are so useful, particularly those that have been refined through phylogenetic research, makes me wonder why we're so attached to common names. Scientific names can be a bit of a mouthful, and simply calling a fish a tiger barb or a black molly is just so much easier. It doesn't surprise me that so many aquarists prefer to stick with those sorts of names.

On the other hand, the endless debates about whether the green spotted puffer is actually Tetraodon nigroviridis or Tetraodon fluviatilis strikes me as rather silly ' as are the not-particularly-descriptive replacement common names like topaz puffier that no-one seems to use consistently anyway. Why not simply refer to each species by its Latin name and leave it at that? Would it really be that difficult for retailers to use Latin names as well, so that shoppers would instantly know what fish was being offered and could then easily look them up in their aquarium books or on the Internet? If we can deal with calling a catfish L.027b, surely we can come to terms with Panaque nigrolineatus.