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Physical Training of Fish to Improve Growth and Production

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By Milthon Lujan

Phylogeny of the fish included in the meta-analysis study. Source: Rodgers and Gomez (2023), Rev Aquac.
Phylogeny of the fish included in the meta-analysis study. Source: Rodgers and Gomez (2023), Rev Aquac.

In the aquaculture industry, the pursuit of efficient growth and production has led researchers to explore unconventional methods. One promising avenue is physical training for fish, which has become a powerful tool to promote growth and enhance production efficiency. However, the nuanced relationship between exercise and growth, coupled with the diversity of species and training protocols, has made drawing universal conclusions challenging.

A meta-analysis of 69 studies covering 31 fish species conducted by scientists at Murdoch University sought to unravel the complexities of the impact of physical training on growth rates and feed conversion ratios (FCR).

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The study’s findings shed light on optimal training regimens and provide valuable insights for fish farmers looking to harness exercise as a strategic management tool.

Contextual Variations in Exercise Effects: Unraveling Complexity

“Swimming exercise can be a promising tool to promote fish growth and overall production efficiency without increasing environmental and economic burdens. Farmed fish can be exercised or ‘trained’ by increasing water velocity to stimulate fish to swim against the current,” emphasize the researchers.

One challenge in understanding the effects of exercise on fish growth lies in the context-dependent nature of these changes. Species-specific responses, along with variations in training protocols such as duration, intensity, and regimen, have created a mosaic of results that can be difficult to interpret. The meta-analysis, spanning a wide range of species, aimed to bring clarity to this complexity.

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Meta-Analytic Revelation: Exercise Enhances Growth Rates

The meta-analysis employed sophisticated tools to extract insights from the amalgamation of diverse studies. The overarching revelation was clear: physical training significantly increases growth rates in taxonomically diverse fish. This finding opens up interesting possibilities for aquafarmers seeking to expedite the attainment of marketable sizes.

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According to the researchers, “Improved growth due to exercise is evident in both salmonids and non-salmonids, with strong effects observed across a wide diversity of species. Additionally, exercise offered the additional benefit of reducing variation in growth rates, suggesting that exercise can be an effective intervention for breeding fish that are not only larger but also more uniformly sized.”

Identification of Optimal Training Regimens

Fundamentally, the meta-analysis identified optimal training regimens to achieve maximum growth benefits. Effects were more pronounced when fish underwent continuous exercise rather than intermittent sessions.

Furthermore, researchers found that the ideal point for target swimming speeds was equal to or less than 2 body lengths per second, and longer exercise durations produced superior results. However, they caution that swimming speeds exceeding 5 body lengths per second incur such high energy costs that energy must be diverted from growth to meet this demand.

“We found that growth gains were higher in fish that were exercised continuously rather than intermittently. Intermittent training, where fish exercise for short periods each day (e.g., 6 h d-1), appears to be insufficient to stimulate higher growth rates,” they emphasized.

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These insights provide practical guidance for implementing exercise regimens in aquaculture operations.

Juvenile Fish: Primary Beneficiaries

Analyses revealed that the positive effects of physical training were particularly relevant for juvenile fish, with an average length of 16 cm in the analyzed studies. This underscores the potential of incorporating exercise in the early stages of life to capitalize on growth-promoting benefits.

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Uniform Growth: A Desirable Outcome

Beyond growth rates, physical training demonstrated an additional advantage: reducing variability in growth. This implies that exercised fish exhibit more uniform sizes, a valuable feature to streamline capture and marketing processes.

Feed Conversion Ratios: Efficiency Unaffected

Interestingly, physical training had no perceptible impact on feed conversion ratios (FCR). Both the exercised group and the control group demonstrated equal efficiency in converting feed into body mass. This finding suggests that while exercise accelerates growth, it does not compromise the fundamental efficiency of food utilization.

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However, the study authors highlight that “since exercised fish grow faster, an FCR equal to that of non-exercised fish may still be beneficial because fish could reach marketable sizes more quickly, potentially improving the efficiency of aquaculture operations.”

Conclusion: Exercise as a Powerful Management Tool

In summary, the meta-analysis of 69 studies provides compelling evidence that exercise is a potent management tool in fish aquaculture. By promoting rapid and uniform growth without compromising feed efficiency, physical training emerges as a strategic approach for producers looking to expedite the journey from juvenile stages to marketable sizes.

Using meta-analytical models, the study shows that, overall, physical training significantly increases growth rates in both salmonids and non-salmonids, with strong effects observed across a wide diversity of fish.

“Optimal training regimens involve continuous swimming (rather than intermittent) at moderate speeds in the water (≤2 body lengths s-1) for fish with an average length of 16 cm,” conclude the researchers.

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As the aquaculture industry continues to evolve, incorporating these findings into operational strategies could mark the beginning of a new era of sustainable and efficient fish production.

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The study received funding from the L’Oréal-UNESCO for Women in Science Fellowship and a Challenge Research Fellowship grant from the Harry Butler Institute at Murdoch University.

Contact
Essie M. Rodgers
School of Environmental and Conservation Sciences
Murdoch University
90 South Street, Murdoch, WA 6150, Australia.
Email: essie.rodgers@murdoch.edu.au

Reference (open access)
Rodgers, EM, Gomez Isaza, DF. The growth-promoting effects of exercise in finfish: A systematic review and meta-analysis. Rev Aquac. 2023; 1-12. doi:10.1111/raq.12879

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