Keys
The freshwater fishes of Iran can be identified using these keys, aided by the illustrations and characters in the "Species Accounts". All keys benefit from use and feed-back - please let me know if you encounter problems.
There are three main sets of keys in this work. There is a general key to families (although all families are recognisable at a glance in Iran with a little experience), a series of keys to genera and species, and keys to regional ichthyofaunas. Genera keys and species keys may be separate if there are many genera and species, or combined in a single key if there are few. Keys to regional ichthyofaunas are convenient in that the number of species is more limited in a region, and errors in using the keys are less likely to occur with fewer steps.
Identification keys are based on couplets, a choice between two alternatives, e.g.
1. Mouth a large crescent; gill membranes joined
to form a free fold over the isthmus = Huso huso
Mouth small and transverse; gill membranes attached to
isthmus---> 2
2. Lower lip continuous, not split in middle;
more than 48 lateral scutes, usually 55 or more; barbels fimbriate =
Acipenser nudiventris
Lower lip interrupted in the middle; less than 51 lateral
scutes, usually less than 45 in Iran; barbels not fimbriate---> 3
If the fish has a large and crescentic mouth, then it is the fil mahi, Huso huso; if not, then the user is directed to the next couplet (2), and so on.
Ideally each couplet has a series of characters which reinforce each other and allow for any loss or damage to characters. Additionally, some characters are "key" but difficult to interpret without experience or are internal and require dissection which is not always possible. In some cases, only one character is available since it must encompass all included species below that point in the key. Since some species are difficult to identify, additional characters are given in brackets [.....]. These additional characters are not unique to the species but, in combination, help to identify the species. Some characters are illustrated in the keys; definitions are given in the Dictionary of Ichthyology.
If used properly, a key is more accurate and less time consuming than flicking through pages of text. The disadvantage of keys is that the alternative state in each couplet is not at hand if you only have one fish to examine, and a simple error can lead you widely astray. Some recognised species have overlapping counts for obvious meristic characters, although means and modes are significantly different, and differ in other, subtler ways not readily summarised in a key. Ideally a student of fishes should collect a series of individuals of different sizes and sexes from each locality, wherever conservation demands and practicality permits. A series of about 30-40 specimens allows for character variations dependent on sex and size, and on abnormalities, and also allows for comparative measurements and counts to be made. And more careful examination may reveal more than one species in the sample.
Distribution is often an important aid in assigning samples to a species. Readers should be aware however that fish farming in Iran has led to the introduction, either deliberately or by accident, of species into basins where they are not native.
The keys should not be used for countries bordering Iran which share many species but also have others not found in Iran.
The most important characters for identification are the general body shape, the number, position and size of the fins, the position and size of the mouth, whether teeth are obvious or not, the number of scales along the flank and the number of rays in various fins, among others. Although colour is often a useful guide, it can also be misleading. Fish vary their colour to match their background or for spawning rituals. In general, it is best to use several characters to identify a fish rather than relying on a single one which can easily be misleading.
Large fishes can be examined for these characters using the naked eye, but various pieces of equipment are necessary for identification of smaller species or juveniles. Hand lenses are of some use in magnifying small characters but by far the best instrument is a binocular microscope which can magnify up to 50 times. Pharyngeal teeth, fin rays and scales can be counted with ease using a microscope. Attachments can be used to take photographs or project images of structures for drawing. Measurements can be taken under a microscope on small specimens to ensure accuracy, and a microscope leaves both hands free to handle the specimen and dissecting tools or calipers. Ichthyologists develop their own techniques for manipulating light sources and specimens for making structures readily visible. I prefer to have two light sources. One of these illuminates the surface of the fish for scale counts and observation of structures. The other bounces light off a white enamel tray into the microscope and is particularly useful for counting fin rays as the light travels through the fin enabling clear distinction of rays.
Two types of forceps are very useful. A large pair (25-35 cm long) enables specimens to be taken out of a jar and sorted without immersing one's fingers. Preservative solutions will irritate the skin and contact should be minimised; some ichthyologists wash the specimen in water before handling, but this may compromise subsequent effectiveness of preservatives. Fine plastic gloves can be worn, but some people develop allergies to latex. A very fine pair of forceps with needle-like points is used to spread folded fins to see the rays and to probe and examine other structures.
Scissors are necessary for slitting the belly and these will vary in size depending on the size of the fish. Fine scissors can be useful in dissection. Very large fish may require a sharp knife or scalpel for dissection or slitting the abdomen. The slit is usually made on the right side of the fish as the left side (head to left) is used for drawings and photographs.
A needle mounted on a wooden or metal handle can be used for cleaning gill arches of debris, clearing flesh from pharyngeal arches or lifting the edges of scales to help in counting them. Most commercial dissecting needles are too blunt and a fine needle can be taped on the end.
Measurements are best made with calipers for accuracy. Dial or electronic calipers are available which measure to an accuracy of 0.1 mm, and are available in several lengths. Very large calipers are usually vernier calipers, but an accuracy of 0.1 mm for large specimens is not required, or even attainable.
Examination of minute scales, debris encrusted gill arches or the lateral and cephalic line canals is facilitated by using compressed air delivered through a glass tube of 1 mm diameter. The air can come from a compressor or aquarium air pump, or even from a hand-squeezed bulb.
© Brian W. Coad (www.briancoad.com)