CM – The secret life of farmed fish

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April 21, 2021

by Georgia MacAulay and Professor Tim Dempster, University of Melbourne

Aquaculture is becoming more and more important as a food source for our growing population. Billions of fish are raised and eaten around the world every year, and people today consume more farmed fish than fish caught in the wild.

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However, as aquaculture production increases, the behavior of many species of farmed fish remains a mystery.

We have both economic and ethical responsibilities to care for the welfare of the animals we raise, but this shortage of knowledge poses great challenges for animal husbandry in aquaculture.

For thousands of years, farmers have been observing and learning from their animals and adapting their farming methods in order to improve the welfare and production of animals.

When livestock behaving abnormally, this usually indicates that something is wrong. For example, a lameness dairy cow will spend more time lying down than a healthy cow.

But the marine life of fish makes it more difficult to care for. They are not seen below the surface, and individuals are anonymous in the huge schools of fish in the tanks and cages in which they are kept.

Tagging fish is not a new practice – tags were first introduced in the 1870s used to follow salmon migration routes. Early days were simple lengths of copper or silver metal attached to the fish’s back muscles. However, with modern electronics, tags have seen rapid and recent technological development.

Tags can now record, store, and forward complex data sets that are measured every second for days or more slowly over months and years.

Tags can measure information that were not previously obtainable – such as heart rate, body temperature, the environment in which fish live, and their position in three dimensions. Some tags can transmit data wirelessly in real time so researchers can see what fish are doing while they’re doing it.

Our group of scientists from the University of Melbourne, the Institute of Marine Research Norway (IMR) and the Norwegian University of Science and Research Technology has used tags to study farmed salmon’s response to parasites, track how salmon swim in new cage environments, and test their ability to learn new behaviors.

This work has resulted in remarkable new discoveries that have improved how fish are treated against harmful parasites, how they react to bad conditions and how fish can learn to adapt to life on farms.

In this work we have found that tags do not always work as intended and that tags sometimes affect the fish negatively.

When tags are supposed to provide useful information n relevant to the entire population of unmarked fish, the behavior and well-being of marked fish must not be impaired by the marking process. However, if tags change fish behavior or well-being, the information they provide may not represent the larger untagged population.

With funding from the Norwegian Research Council, we have systematically reviewed studies that use tags to monitor farmed fish behavior First, in studies in sea cages where fish are kept, the mortality of tagged fish was ten times higher than in tanks. The aquaculture of sea cages is carried out in floating cages that are attached to berths in the sea that are open to the wider marine environment.

In sea cages, one in four tagged fish died within the study period. In general, the longer the investigation, the higher the death rate. In many studies, key information such as the death rate of tagged and unmarked fish was not reported, making it difficult to determine the effects of tagging.

Why are sea cage death rates so high and why are they different from tank studies?

Experiments carried out in small tanks are usually carried out under controlled culture conditions, where researchers can largely prevent poor water quality and other undesirable events such as algal blooms or environmental pollution.

In comparison, experiments carried out in large sea cages in the ocean filled with thousands to millions of individuals, fish from stressful environments (fluctuating temperature, salinity, dissolved oxygen, electricity, pollutants, and pathogens) that can affect their behavior, well-being, and survival.

(ii) high deaths Probability rates in sea cage experiments call into question how representative tagged fish are for the entire fish population; and

(iii) With such high death rates in tagged fish in sea cages, tagging in this environment creates significant welfare problems.

Tagging is stressful for fish – being caught, handled, and surgery are not experiences a fish would normally go through. In sea cages, fish are also exposed to other stressful conditions such as crowds or extreme environmental influences – and unlike wild fish, cage fish cannot swim away from uncomfortable conditions.

We believe that the additional stress factors in the vicinity of the sea cage make it difficult for the fish to to recover from the initial stress of tagging and that this leads to a lower chance of survival.

Based on our results, we recommend a more rigorous application of the 3Rs when tagging fish in aquaculture. These are the guiding principles for the humane use of animals in scientific studies and include:

In our review published in Reviews in Aquaculture, we suggest tagging where possible through unobtrusive behavior monitoring technologies such as sonar, video or computer To replace imaging.

These alternatives will not work for every study. If researchers need to use tags, we recommend keeping the number of tagged fish to a minimum that will still provide large enough sample sizes to produce relevant results.

We also have recommendations for future tagging research to Refine the tagging process by encouraging researchers:

By reporting this information, researchers should be able to determine whether tags are adversely affecting the welfare and survival of their test fish – and whether it is a good idea to take data from Using fishing to make assumptions about unlabeled fish.

Our results shed light on a practice that is becoming increasingly popular – but one that needs significant improvement to ensure that it is a safe method for fish that also provides reliable results.

As tagging technology becomes cheaper and more sophisticated, tags will continue to be a popular choice ner to be scientists researching farmed fish. Tagging, while showing promise, needs significant improvement to ensure the welfare of tagged fish in aquaculture.

John R. Moring. Marking experiments with Atlantic salmon in the United States in the 1870s and 1880s, Fisheries (2004). DOI: 10.1577 / 1548-8446 (2002) 027 2.0.CO; 2

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