Have you ever wondered if it's possible to move Arctic char into brackish waters earlier without the fish suffering? Well, recent research conducted by the Experimental Farming Station of the Marine Research Institute in GrindavÃk has shed very promising light on this topic, suggesting that we can move these fish much earlier in their juvenile stage than previously thought.
This discovery is no small matter, as it could be a game-changer for fish farmers in areas like Reykjanes. In these locations, obtaining fresh groundwater is a real headache, so knowing that Arctic char (Salvelinus alpinus) tolerates salinity well from a young age opens up a range of possibilities for scaling up production without so many water restrictions.
The experiment: How was the test conducted?
To resolve any doubts, a detailed study was designed and published in the journal Aquaculture . The objective was to see if the fish of the Hólastofn population could transition from very low salinity (3‰) to a glacial water concentration (20‰) at a very early stage of their growth , instead of waiting until they weighed between 100 and 200 grams, which is the usual practice.
The experiment involved 432 tagged fish, divided into two distinct farming strategies:
- A first group was transferred to the brackish water when they were just "babies" with a average weight of 8 grams.
- The second group remained in fresh water (3‰) until they were much larger, reaching about 176 grams before transport.
For more than 500 days, scientists kept a close eye on the specimens, monitoring critical aspects such as growth rate, survival, whether they reached sexual maturity and, especially, the health of their bone structure until the moment of sacrifice.
Analysis of the results: Growth and survival
Looking at the growth data, it initially appeared that the prematurely transferred fish were growing more slowly than their freshwater counterparts. However, over time, this gap narrowed. In fact, from day 328 onward, there were no significant differences in growth rate between the two groups.
At the end of the process, something curious happened: the group that spent more time in freshwater ended up weighing an average of 1252 grams, while those transferred earlier weighed 1063 grams. Although the weight difference remained , it's important to note that the length of the fish was practically the same. But what really matters here is that survival rates were comparable in both cases; the small, 8-gram fish withstood the 20‰ salinity treatment without a significant increase in mortality.
Bone health: The key finding of the study
This is where the research gets really interesting. It turns out that the timing of the transfer drastically influences bone formation. In those fish that were moved to saltwater later, malformations were found in 13% of the individuals , a considerably high figure.
Conversely, specimens that transitioned at a very young age showed a malformation rate of only 2% . This means that waiting too long to move the fish increases the risk of developing bone problems fivefold, making early relocation much healthier for the animal.
Given that much of Iceland's Arctic char production is concentrated on the Reykjanes Peninsula, where freshwater is a limited resource, leveraging the fry's ability to adapt quickly to brackish water is a brilliant alternative to boost the industry and optimize available resources without compromising the species' welfare.
Evidence shows that advancing the transition to brackish water is not only viable and safe in terms of mortality, but also drastically reduces bone malformations and allows for the optimization of groundwater use, enabling fish to reach similar marketable sizes despite a slightly slower initial growth rate.