Freshwater Fishes of Iran

Introduction - Preserving Fishes

Revised:  27 June 2007

Acknowledgements     Purpose     Materials and Methods     History of Research     Fisheries     Geography     Climate     Habitats     Environmental Change     Drainage Basins     Scientific Names     Fish Structure     Collecting Fishes     Preserving Fishes     Quotes

Captured fishes which cannot be identified or seem unusual enough to warrant further attention should be preserved. Labeled, preserved specimens deposited in a museum are a permanent record of species identity and distribution. Some taxa present problems of identification even for experts so that misidentifications are often a nuisance if there is no material to examine. There is a developing aquarium industry in Iran that imports fishes from Singapore and Malaysia. There is a potential for exotics to become established as there are no controls or statistics are not kept (Tehran Times, 28 July 2001). Various exotics are now established through the aquaculture industry (Coad and Abdoli, 1993b). Samples from ecological or experimental studies as well as systematic and distributional works may be preserved and sent to a museum where their identity can be confirmed and where they are available to workers in the future. The National Museum of Natural History, Tehran (Muze-ye Melli-ye Tarikh-e Tabi'i) has a small collection of Iranian fishes but it is not extensive enough for systematic studies. Major museums in a number of countries welcome exotic material to enhance the variety of their collections. The author would be happy to identify fishes from Iran and the Middle East.

Specimens should be preserved whole, without removal of the guts or gills so that no key characters are lost. Specimens may be frozen, or even salted, but the best method and the one used by scientists is to drop fish into 1 part full-strength formalin to kill the fish quickly and then immediately add 9 parts of water to form a 10% preserving solution. Large specimens (larger than about 15 cm) should have a small slit made in the right side of the belly to allow formalin to penetrate the tissues. Ichthyologists cut the right side of the fish and leave the left side undamaged for illustration and scale counting. Hypodermic syringes are used to inject the abdominal cavity and muscle blocks of very large fish with formalin, otherwise the preservative will not penetrate all the tissues before decay sets in. This is especially important in a hot climate like that of Iran. Syringes should have a capacity of up to 100 ml and be capable of taking needles of various sizes. Particular care should be taken when injecting formalin into tissues; the needle should be withdrawn gradually while injecting the formalin solution to avoid a sudden spurt of liquid under pressure from the injection site.

Wherever possible some specimens should be preserved in 95+% ethanol or other appropriate solutions for potential molecular studies. Modern DNA techniques may be the only way to resolve some systematic problems as morphology has proved inadequate.

Formalin should be handled with care as it is a noxious chemical which irritates the eyes and nose and is painful in skin cuts. It may be carcinogenic and repeated exposure can trigger allergic reactions in the skin. Gloves and safety glasses are useful when diluting full-strength formalin. It should only be handled in well-ventilated rooms or in the open air. In the field, care should be exercised in packing specimens for transport so that leakages do not occur. Long-term preservation in formalin is not advisable as the solution becomes acidic and rots the fish. It also wrinkles and hardens the specimens.

Most museums store their specimens in alcohol for the long term. The formalin-fixed specimens are washed briefly in water and then transferred to 45% iso-propyl alcohol or 70% ethanol. These chemicals are pleasanter to work with. Some care should be taken such that specimens are not twisted and bent inside the preserving container. It is difficult to make counts and measurements necessary for identification on badly deformed specimens. Each specimen or group of specimens should have at least an equal volume of preservative as water in the fish tissues tends to dilute the preserving fluid. Specimens may be stepped through 30%, 50% and 70% alcohol solutions to reduce wrinkling and ensure a fuller penetration of alcohol into tissues and a final storage solution of at least 70% ethanol. Ethanol may be difficult to obtain in Islamic countries and undrinkable iso-propyl alcohol can be substituted.

The best containers for long-term storage are made of glass with tightly-sealing polypropylene lids. Plastic containers deteriorate with time and tend to crack. Metal containers and metal lids eventually rust. In the field, large plastic buckets with tightly-sealed lids are less likely to break than glass containers and are not as heavy. Very large fish may require sone sort of drum, such as a clean oil drum but it should be noted that formalin corrodes metal and the drums should be lined with plastic or lacquered. Fluid levels in the collection should be checked regularly and alcohol concentrations maintained at the recommended values or the specimens will deteriorate. Collections should be kept in the dark to reduce fading of pigments and at a constant, cool temperature.

Fish which have been preserved for a week in formalin, more for larger fishes, or transferred to alcohol can be sent to a museum for identification. Glass containers full of formalin or alcohol should not be mailed because of the danger of breakage. The fish should be wrapped in cheesecloth or some other absorbent packaging, with its label, the cheesecloth dampened with preservative, and tightly sealed in several, leak-proof plastic bags before being placed in a padded box for mailing. Spiny fish should be especially well wrapped to avoid puncturing the plastic bags. A tightly-sealed package retains the preservative which keeps the fish in good condition. The box may be labelled "Scientific specimens, no commercial value".

The label is as important as the fish itself. An interesting specimen is of little or no scientific value if there is no locality data. Labels should be written at the time of capture. Faulty memory and good intentions to label specimens later make a poor combination and often result in collections with no data, or worse with incorrect data. The label should bear the place of capture, such as a stream, lake, spring, qanat, etc., including a reference to the nearest town (local names may not be on maps or in gazetteers and some village names are very common, e.g. Hoseynabad, of which there are over 170 in Iran!), latitude and longitude, province, date, name of collector, notes on the habitat and live colour of the specimens, and any other items likely to be useful. Colour photographs of fresh fish are most useful, especially if the fins are pinned erect. Pencil or India ink should be used on stout, waterproof paper which will not disintegrate in liquid. The label must be dropped in the jar with the fish. Labels on the outside of jars always fall off and lids with labels always get put on the wrong jar!

In fact the amount of information which should be usefully recorded cannot be put on a small label. Instead extensive field sheets are used and related to the specimen or sample by a field number. The Canadian Museum of Nature, Ottawa (formerly National Museum of Natural Sciences) has field sheets with over 70 categories which can, potentially, be filled in and some categories have as many as 30 alternatives, e.g. Category 17, Environment includes fresh spring, cave, canal, stream/river, river-lake junction, flooded area, fresh pool, pond, lake, marsh (treeless), swamp (with trees), reservoir, ditch, etc. (see below). As an insurance against loss of field sheets or confusion of numbers, the jar label should carry minimal locality data as well as the field number.



Brian W. Coad (