Some fish parasites

[samir]

Hope this helps the less experienced and more confused understand better the life cycles of some common pests in order to completely eradicte them.
Introduction.

The skin of fish consists of two layers of different composition namely, the epidermis (the upper part) and the cutis (the lower part). The epidermis consists of epithelial cells with mucous cells in between. These mucous cells excrete a slimy substance that covers the whole surface of the skin, with a protective layer. This mucous coating helps to protect the fish against infections. However certain parasites make fish their host, they feed and live on the fish and some even reproduce on the fish. Other parasites leave the fish to reproduce, but the youngsters soon scurry back to find a new fish host.

Representatives of all major groups of parasitic protozoans use this external surface or the internal tissue of the fish integument as an environment. We will look at several of these ectoparasites to examine how they survive on fish.

Although Parasites affect all fish in various environments this project is aimed at Koi in British ponds in particular.

Trichodina.

This pathogen is a high hat shaped ciliate crowned with a ring of cilia at each pole of the cylindrical cell. It can be easily seen at 100x magnification.

Trichodina continually spins and can quickly change from place to place on the fish. The parasite moves about it’s host by means of the ciliary girdle, which also serves to propel it through the water. On the underside of Trichodina there is a complicated attachment organ known as the adhesive or sucking disk. It can be easily seen at 100x magnification.

They reproduce by both binary fission (dividing in two) and conjugation, it appears that reproduction is not a simple procedure for these protozoa. Fish have a resistance to the propagation of parasites, but bad conditions in the pond is an ideal environment for Trichodina. As the fish makes more mucous to protect itself, so the bacteria will increase and in so doing will provide ideal conditions for the propagation of Trichodina. Presence of large numbers of this parasite is indicative of poor water quality and/or overstocking and often occur with other ectoparasites.

Fish Louse. (Argulus).

This parasite has a flattened body with eight legs with which it swims and a small fish like tail which acts like a rudder. It has two large hooks for attaching itself to the fish and between it’s pair of eyes it has a proboscis which it forces down under the scale of the fish and into the cutis area. It then feeds by sucking up the fishes blood. Argulus can grow up to 10mm in diameter, but usually they are about 7mm.

Mating takes place between late Spring and Summer and the eggs are deposited in long tubes, which are flatish, on to the sides of the pond.

The females die after spawning while the eggs hatch out about a month later. The louse is capable of attacking fish at about one month old. The louse is also old enough to mate and can cause heavy infestations which can cause mass mortalities. This parasite is also a strongly suspected spreader of virus diseases.

Gill Fluke. (Dactylogyrus).

This parasite is worm shaped and normally makes it’s home in the gills of the fish, where it also feeds on the gill plate and causes serious gill tissue damage. Such damage prevents the adequate diffusion of oxygen and causes many secondary gill problems. Eggs laid by the fluke embryonate and hatch in a period which varies with temperature. In certain climates eggs laid in Autumn can overwinter and hatch out in the Spring when more favourable conditions arrive.

The larvae propel themselves through the water until they find a new host and can survive for about four days in normal water temperatures without a host fish. The feeding of this parasite destroys the epithelium, causing haemorrhagic ulcerative lesions but is not usually harmful to large fish.

The four eye spots are recognition features that help to differentiate between the body and gill fluke. The eggs of this fluke hatch out in about four days at a temperature of 20oC or longer if the weather is colder. It can be easily seen at 100x magnification.

Costia. (Ichthyobodo).

This parasite is probably the best known serious fish pathogen which causes the disease Costiasis. They are very fast moving and the swimming stage is oval to kidney shape with two pairs of flagella of unequal length. The two longer flagella are used to create movement which results in a jerky motion. When attached to the fish it is without obvious flagella and penetrates the epithelial cells with a type of hold fast organ.

Reproduction is by division and they may be that rapid that in one or two weeks the fish is covered with specimens of this parasite and unless treated the fish will surely die. This costia parasites reproduction temperature range is between 10oC and 25oC, below 8oC the organisms encyst whilst at 30oC they apparently cannot survive.

The life cycle of costia is completed in ten to twelve hours at 26oC but takes six days at temperatures of 4oC. It can be seen at 100-400x magnification.

White Spot. (Ichthyophthirius Multifiliis).

This parasite penetrates the mucous coat, the epidermis and the cutis, where it feeds on red blood corpuscles. When full grown it bores out through the epidermis for reproduction. The mature white spot sinks to the bottom of the pond where it covers itself in a jelly like substance called a cyst. Within this cyst the parasite undergoes a rapid division into numerous youngsters which can number up to two thousand. Depending on the temperature for hatching the young parasites will be free swimming and soon looking for a new host fish.

At 75oF the cycle will be around four days, whilst at 45oF the cycle will be nearer to forty days.

The white spot viewed from above or below is circular and has a large number of cilia (little hairs) and by the movement of which can swim and move around the fish. It then penetrates into the skin of the fish via a tubular mouth. The feeding stage of the parasite is found within the epidermous of the skin and therefore is safe from treatments making it the most important ciliated protozoan. This parasite can only be treated in the free floating stage.

Anchor Worm. (Lernea)

Only the females of this parasite actually parasitises the fish, she has a long body with an anchor like appendages at the head. By means of these the adult sticks to the fish since the anchor penetrates under the scale and into the muscle of the fish, where it feeds.

Reproduction takes place in May/June whereby the male anchor worm then dies. Two egg sacs are produced at the end of the females body, from these eggs the larvae hatch and swim freely until they come into contact with the fish, they then commence the cycle again.

The adult female still feeding on the host fish then soon dies, often leaving large holes with round openings in the muscles of the fish. These wounds sometimes heal very slowly but often become infected with bacteria and fungus and unless treated will often die from these secondary infections.

Skin or body fluke. (Gyrodactylus).

A worm like parasite which fastens itself to the fish by means of small hooks and then drives two larger hooks into the fish to obtain a firm hold. It feeds on the epithelial cells and when it wishes to move on it does so by a looping action. This parasite is a remarkable livebearing organism for not only can the young fluke be seen within the body of the adult, but in the unborn body yet another embryo may be seen. The young parasite creaps out into the mucous immediately after birth and can produce another youngster after only one day and then every four to five days. They live for about twelve to fifteen days at temperatures between 59oF and 68oF and are easily treatable.

This fluke is not thought to be a serious or significant pathogen in properly controlled systems and are not a problem unless really heavy infestations are present.

Leech. (Piscicola geometra).

A long worm like creature with a membered body which has a sucking disc at both ends. Movement of this parasite is by means of looping like a caterpillar. Leeches feed on blood and can also be bearers of blood parasites. They lay there eggs in cocoons on the pond bottom, plants, stones, etc. The leech is not an obligatory parasite and may leave their host for long periods of time, as they can survive for prolonged periods without feeding. The greatest threat to the fish from the leech is caused by moving from fish to fish whilst sucking blood, with a great risk of spreading any virus diseases present to all the fish in the pond. Leeches are common in planted ponds and are less likely in non planted ponds. They can infect all parts of the fish including the mouth and gill areas, and this parasite is extremely difficult to eradicate. The life cycle of Leeches can take from a month to more than a year depending on the species and temperatures of the water. Studying temperatures at which the parasites life cycle is speeded up so as to pitch the use of chemicals accurately is one option of eradicating them, the other alternative is to completely strip down the whole system and allow it to dry out.

Chilodonella.

Chilodonella is another important ciliate ectoparasite on a wide range of freshwater fish. It has a flattened ovoid shape and is covered by rows of cilia which move it in a steady gliding manner over the epithelial cells on which it feeds.

They reproduce primarily by binary fission and favour temperatures between 5oC and 10oC for optimum reproduction. It can therefore cause problems and be a serious pathogen to over wintering carp.

Conclusion.

As we can now begin to understand these parasites, if allowed to get out of hand can result in further problems of disease and at some time or other the koi-keeper has to deal with disease amongst his/her fish. We will now look at which of the ectoparasites we have looked at to hopefully find which of them is the most pathogenic to koi and why.

Chilodonella must rate as the most dangerous of the skin parasites as it can actively swim short distances and consequently spread to other fish. The risk of infection is increased if ponds are over stocked. In debilitated fish the disease quickly becomes established and may spread to healthy fish as well. In severe cases the skin may eventually fall away in strips. The gills can be totally destroyed so that only the cartilaginous parts of the gill lamellae remain. Also with it’s reproduction temperature between 5oF and 10oF, most treatments are inactive.

Costia is also a serious contender as one most pathogenic to koi as it reproduces fairly rapidly and in large numbers causes osmoregulatory failure leading to death.

White spot is a very important ciliated protozan and it is impossible to remove chemically without killing the host fish. Treatment is only effective on the life stages outside the dermal tissue of the fish. Fish are normally infected during autumn/spring and it is when this parasite enters the gills, which if extensively damaged can cause death.

Alteration of the protective barrier will also allow opportunistic bacteria or fungi access to underlying tissues and fish may die through secondary infections.

Anchor worm leaves largish holes when they die and bacteria etc can penetrate right through to the muscle. Fish lice in sufficient numbers can cause mortalities by sucking out the blood and leaving open wounds for secondary infections to penetrate and as it travels from fish to fish may also be a spreader of viruses.

All ectoparasites that damage the epidermis and/or cutis areas of fish are pathogens to be aware of. They open up areas where secondary infections and often more serious problems can arise, bacteria and viruses are waiting to invade and take advantage of any situation no matter how smal

[Merrilyn]

Great post Samir, thankyou. I've made it a sticky so all members can easily find it.

[marg]

You've done it again Samir!!

Aren't we lucky to have someone like you who is prepared to research subjects that interest us all and help us make life better for our precious fish .

Thanks heaps, keep up the great work - we all appreciate it very much.

Regards,

Marg.

[JoeDiscus85]

Samir i do have to say you have completely and totally outdone yourself this is some really usefull and potentially life saving information for the discus that is. Thanks for your hard work and keep it Samir


Joe