Fish Diseases and Management

Collection of samples for histology

Collect the samples with minimum handling. Collect only live animals as far as possible. The samples are fixed or preserved in a fixative having 10 times volume that of the volume of the tissue. Common fixative used for shrimps is Davidson’s fixative (Alcohol Formalin Acetic acid – AFA fixative)

Larvae and postlarvae (PL)

Immerse the shrimp directly into the fixative in case of larvae and postlarvae (PL). Fix for 12 to 24 h in a minimum of 10 volumes of fixative to one volume of shrimp tissue for effective preservation. Then transfer to 70 % alcohol for storage.

For PL that are more than 20 mm in length, make a small and shallow incision in the back using a fine needle and slightly lift the cuticle in the midline at the cuticular junction between first abdominal segment and cephalothorax. This is needed for quick and proper penetration of the fixative into the hepatopancreas.

Fixation of juveniles and adults:

If possible, place the shrimp briefly in ice water for sedation. Fixation is done by injecting the fixative into the body of the live shrimp, using a needle and syringe. Depending on the size of the shrimp, 0.1 ml to 10 ml of fixative is injected (approximately 10% of the shrimp’s body weight). The site of injection should be anterior and posterior abdomen, anterior hepatopancreas and proper hepatopancreas. The shrimp should be properly fixed indicated by the change of colour. After the injection, slit open the shell. If the shrimp is larger than 12 g, bisect it at the junction of abdomen and cephalothorax. Immerse the shrimp in the remaining fixative. After 24-72 h and proper fixation, the specimen should be transferred to 70% ethyl alcohol. For transportation, remove the specimen from alcohol and wrap it in paper towels. Place the wrapped specimen in a sealable plastic bag and saturate it with 70% alcohol. Write complete history of the specimen and place the bag in a second sealable plastic bag. Many small sealable bags can be kept in one large sealable bag. This can be further transported to lab for processing.