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Histology is the examination of changes in the tissues of fish. These may be due to infection, tissue damage, haemorrhage, etc. Different diseases damage the tissues in different ways, which means that histology may be used as one of the tools for making a diagnosis. Combining real-time RT-PCR with histology thus provides new potential for ascertaining the nature of disease.

Why histology?

Histology expands the advisory and problem-solving capability that PHARMAQ Analytiq offers to the industry. Health challenges in the aquaculture industry can often be ascribed to a number of different factors. By examining the tissue response of the fish in combination with any infectious matter which is present, one can draw conclusions about what may be the greatest challenge to the fish’s health. This may be decisive for implementing the right preventive measures at the right time.

In the case of known diseases such as infectious salmon anaemia (ISA) and pancreas disease (PD), the level of virus presence will often provide a clear indication of what causing fish mortality. Nevertheless, it may be necessary to submit histological documentation to the public authorities in some cases. In the case of other diseases in which the significance of the amount of infections matter is less well known, histology in combination with real-time RT-PCR will provide a better overview of the overall pathological picture.

Histological cross-section of lumpfish fry

Cross-section of lumpfish fry

Rapid analysis result provides more possibilities

Before planned handling such as delousing, moving or sorting, it is important to carry out a risk assessment. Examination of damage to gill and heart tissue provides an insight into the tolerance of the fish and can affect a decision as to whether to postpone handling or perform it with additional caution. A fish whose heart appears as shown below has reduced cardiac capacity but will often display no signs of illness in a normal hatchery situation. During delousing or other stressful operations, such fish may die as a result of their impaired cardiac function. A quick risk assessment is more feasible now than it used to be, since, as in the case of real-time RT-PCR, the standard response time for histology is five days.

Photograph of histological examination of a salmon heart with heart and skeletal muscle inflammation (HSMI)

Heart showing HSMI. Cell-rich inflammation at the surface and spreading towards the interior of the heart.

Long experience with diagnostics

Renate Johansen is head of histology services at PHARMAQ Analytiq. She has 14 years’ experience in fish diagnostics and research at the Norwegian Veterinary Institute and the Norwegian School of Veterinary Science, as well as practical experience in the field.

Renate Johansen
Histology Services Manager

Fish tissue answers many questions

Studying the tissue response (histology) of fish provides answers to many questions about the state of the fish’s health and welfare. Histology is therefore an important tool which in combination with PCR provides a good picture of a fish’s condition. The demand for histology is therefore increasing sharply and PHARMAQ Analytiq is pleased to have Pernilla Simolin as a member of its histology team.

Trygve Poppe

Trygve Poppe – Expert Advisor at PHARMAQ Analytiq

After many years as a professor at the Norwegian School of Veterinary Science, Dr. Trygve Poppe has now been appointed as an expert advisor at PHARMAQ Analytiq. Poppe is particularly well known for his excellent teaching of students in fish health and veterinary science and has also published several books about fish health.

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