FISH CRUSTACEA

Like humans and other animals, fish suffer from diseases and parasites.

All fish carry pathogens and parasite. Usually this is at some cost to the fish. If the cost is sufficiently high, then the impacts can be characterized as a disease.

Parasites in fish are a natural occurrence and common.

Almost all fish are potential host to a wide range of parasites.

When the population of the fish parasite grows beyond a certain limit, it can be life-threatening.

Also, fish can transmit some parasites to human “zoonotic parasites”.

Parasites

Fish

Helminths

Arthropods

Protozoa

Leeches

Trematodes

Cestodes

Nematodes

Acanthocephalans

Crustacean

Ciliates

FlagellatesMyxozoa

Coccidian

Monogenea

Digenea

IMHFH

Fresh water

Marine

Microsporidia

There are about 42,000 species of Crustacea, including many of the most familiar arthropods such as the crabs.

Crustacea is the only group of arthropods that is primarily marine, though there are many fresh water species.

Reproduction of Crustacea occurs after a number of larval stages, crustaceans metamorphose into the adult, usually after settling on the sea floor.

The sexes are usually separate in Crustacea, and sexual dimorphism is clear but some crustacea are hermaphroditic.

Ectoparasitic crustacea1- Copepoda 1- Ergasilus 2- Caligus 3-Lernea 4- Salminocloa

2- Branchiura Argulus sp. (Fish Lice)

3- Acarina Larval stages of water mites

Class Copepoda

The copepods are mostly marine.

They occur in vast numbers, millions being present in a cubic meter of sea water and are important links in many food chains.

The copepod body is short and cylindrical, and as in all crustaceans, is segmented comprising a head, a thorax and an abdomen.

The head and thorax are often fused to form a cephalothorax.

There is a long pair of antennules and a shorter pair of antennae (at the front of the body.

Diagram showing morphology of Copepods

Diagrammatic life cycle of Fish-parasitic copepodes “crustacea”

Arthropods Crustacean: Copepods; and Branichura

Ergasilus spp. Argulus spp. Caligus spp. Salminocola spp. Lernea spp.Gill louse Fish louse - - Anchor worm

Gills Skin Skin Gills Skin, fins

Cyclop like, with 2nd antenna modified to be hook like.

Egg sacs in female is attached to the abdominal segment

0.5 to 1 cm in length It has 2 sucker like adhesive discs, eyes and in the thoracic part 4 pairs of swimming legs.

Up to 1 cm in length, oval in shape with anterior cephalothorax being the widest part, followed by abdomen which is constricted end with 1 pairs of swimming leg-like structure. In female the egg sacs usually on the form of tape like.

It exhibits a maxilliped with subchela that ends as a solid claw. The claw is associated with a long papilla. The copepod possesses a large, flat, and round bulla associated with two maxillary arms.. At the termination of the antennae, there are hook-like processes on the endopods. The 2nd maxilla is relatively long and is implanted up to 2/3rds of its length in cavities of 5–8 mm in host tissue

10 to 12mm with characteristic anterior end (Head), which have horns like projections, while the rest of the body cylindrical and elongated.

In female, egg sacs are attached to the last abodominal segment

Ergasilus sp. is a member of a small group of parasitic crustaceans that prey upon freshwater and marine fishes.

It may be found on the skin, fins, and gills of fishes, but is most frequently found on the gills.

They can cause significant morbidity and mortality when heavily infesting fish.

They have also been implicated as vehicles for other fish diseases.

Ergasilus has a direct life cycle using only fish as a host.

Ergasilus can spend prolonged periods swimming free, and mating takes place while the male and female are swimming. The male then dies. Egg incubation occurs while the egg clusters are attached to the female. 

(Ergasilus sp.)

Adult female Ergasilus on gill of rainbow smelt.

The offspring hatch and are broadcast into the water.

The offspring undergo four molts before becoming adults.

There are several species of Ergasilids and none is too host specific.

Ergasilids infect wide range of fish species like eels, herrings.     

(Ergasilus sp.)

Male Ergasilus.

Affected fish have patches of hemorrhagic and edematous affected skin, gills or fins.

The parasite causes these injuries by attaching to the fish with its modified antenna turned hooks. Its feeding apparatus further injures the host fish when it inserts the stylet into the epidermis and underlying host tissue causing hemorrhage.

Ergasilus feed on the host’s blood and body fluids. 

The feeding apparatus also may release digestive enzymes which can cause systemic illness  similar to Argulus.

(Ergasilus sp.)

Special points of interest:Ergasilus does not infect humans.

Ergasilus sp. can be found on the gills of many different species of freshwater fishes.

Cooking fish kills the parasite.

(Ergasilus sp.)

Gill Louse )Gill Louse )SalmonicolaSalmonicola sp.( sp.( Gill Louse )Gill Louse )SalmonicolaSalmonicola sp.( sp.( These are copepod organisms

Salmonicola attach to fish by burrowing an attachment organ called a “bulla” beneath the skin or gill tissue.

This bulla anchors the young Salmonicola organism in place generally to a part of the fish’s bone or cartilage. It lives its entire life then in that spot on the fish. 

Damage to gill tissues can be extensive, and result from attachment , feeding, and the mechanical presence of the parasite. The parasite feeds on the fish’s body tissue and body fluids.

As the parasite grows, the females develop two caudal egg sacs. These can be easily seen with the naked eye. In some species of Salmonicola the egg sacs are dark brown to black in others they are cream to tan in color.

Salmonicola have a direct life cycle.

The egg sacs on the caudal portion of the female’s body release eggs into the water column.

The eggs develop into larva within the egg shell and then hatch ready to infect a new fish. 

The young parasites die within a day or two of hatching if they do not find a suitable fish host.

Gill Louse )Gill Louse )SalmonicolaSalmonicola sp.( sp.( Gill Louse )Gill Louse )SalmonicolaSalmonicola sp.( sp.(

Salmonicola Salmonicola sp. sp. Salmonicola Salmonicola sp. sp.

    Salmonicola edwardsi infestation on gill of  landlocked Atlantic salmon.

Learnaea - Anchor wormis a common parasite on fish which is clearly visible to the naked eye and can reach 10 to 12mm.

The parasite burrows its head into the fish tissue, under a scale and only the body and tail are normally visible.

If left on the fish, secondary bacterial infections can occur at the point of contact due to the damage caused by the anchors used to attach itself.

Learnaea lay eggs which can lay undetected in the pond and can hatch when conditions and water temperatures are right.

Chemical treatments will not affect the viability of eggs so repeat treatments may be required to kill all generations.

Normally the parasite attaches itself by the dorsal or tail fin, and is also commonly found in large numbers on the bellies of fish when they are first netted from the mud ponds.

Learnaea - Anchor worm

Treatment is by manual removal of the parasite with tweezers under anaesthetic, ensuring that the whole parasite is removed.  To be sure of complete removal, dip a cotton bud in strong potassium permanganate solution and dab the worm with this solution whereupon it will release its grip immediately.  Pond treatments.

Caligus spp. is an opportunistic parasite and like its close relative the salmon louse, cause problems for both wild and farmed fish in the northern Atlantic.

Caligus spp. has been found on more than 80 different fish hosts. With an increased number of fish farmed in marine waters, the infection pressure from this parasitic copepod is likely to increase.

Caligus spp.Caligus spp.

Caligus attached to the host

Class: Branchiura

The branchiurans are flattened crustaceans which are temporary parasites on fish.

Like most parasites many features have become reduced; the eyes are sessile, the antennae are very small, the abdomen is small and unsegmented and there are no gills.

Morphology of Argulus sp. (Fish lice)

Fish Louse )Argulus Sp.(

Live Argulus from skin of largemouth bass.

Argulus Spp.

is a member of a small group of parasitic crustaceans that prey upon freshwater and marine fishes.

Argulus can be found on the skin, fins, and gills of fishes.

They can cause significant morbidity and mortality when heavily infesting fish.

They have also been implicated as vehicles for other fish diseases.

Fish Louse )Argulus spp.(

Argulus spp. has a direct life cycle using only the fish as a host.

Argulus can spend prolonged periods swimming free and mating takes place while the male and female are swimming.

Clusters of Argulus eggs are deposited on submerged objects and after hatching, juveniles must locate a suitable host within a couple of days or they will expire. 

Fish Louse )Argulus sp.(

Fish Louse )Argulus sp.(

Argulus can be seen moving rapidly around on the surface of the fish, but will often swim away as soon as the fish is netted out of the water. 

Affected fish have patches of hemorrhagic and edematous affected skin, gills or fins.

The parasite causes these injuries by attaching to the fish with its curved hooks and sucker.

Its feeding apparatus further injures the host fish when it inserts the stylet into the epidermis and underlying host tissue causing hemorrhage.

Argulus feed on the host’s blood and body fluids.

The feeding apparatus also releases digestive enzymes which can cause systemic illness.

Fish Louse )Argulus Sp.(

Live Argulus from skin of largemouth bass.

Argulus Spp.

is a member of a small group of parasitic crustaceans that prey upon freshwater and marine fishes.

Argulus can be found on the skin, fins, and gills of fishes.

They can cause significant morbidity and mortality when heavily infesting fish.

They have also been implicated as vehicles for other fish diseases.

Fish Louse )Argulus spp.(

Argulus spp. has a direct life cycle using only the fish as a host.

Argulus can spend prolonged periods swimming free and mating takes place while the male and female are swimming.

Clusters of Argulus eggs are deposited on submerged objects and after hatching, juveniles must locate a suitable host within a couple of days or they will expire. 

Fish Louse )Argulus sp.(

Control Measures

Don’t transport fish from one water to another without hygienic measures.

Don’t dispose of fish parts into water - it can spread the parasites eggs.

Clean boats and equipment before moving between different waters.

TreatmentExcept for Laernea spp. which required manual removal of the parasite, nearly all ectoparasitic crustacea could be treated with

3% salt dip, followed by 0.2 %-prolonged bath for three weeks.

Other chemicals like Potassium permanganate, formalin and cupper sulpahte can be used as short dips with diluted or very diluted concentrations.

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