# A Study Toward More Ethical Commercial Aquaculture by Leveraging Rheotaxis

## TL;DR

This paper introduces a prototype system that uses water currents to guide fish, reducing the need for physical handling and improving fish welfare in aquaculture.

## Contribution

A novel system leveraging rheotaxis to enable hands-free fish movement and monitoring, improving welfare and commercial viability.

## Key findings

- Rheotaxis effectively moves striped bass through a channel for observation without physical handling.
- Fish showed less behavioral variability and more frequent movement with directed currents.
- The system allows early identification of malformed fish for humane culling.

## Abstract

Current practices in aquaculture require physical handling of fish for routine measurement and health monitoring practices. These practices are labor-intensive and risk the welfare of fish by increasing both stress and the risk of significant injury. We have developed a prototype that is part of a larger system to eliminate the need for physical handling during measurement, health monitoring, and grading of farmed fish. With this prototype, we test the viability of using innate behavior in response to directed water currents (rheotaxis) to move fish through a channel, which will serve as an observation point. In the future, data will be collected at this point to determine measures such as length, indicators of health, and the population size. Results show that rheotaxis is an effective mechanism to move striped bass through a channel and past a point of observation. Further, this result indicates potential in the area of hands-free, autonomous sorting of fish as we continue to explore more fine-grained directional control of these fish.

The welfare of farmed hybrid striped bass remains largely unaddressed in U.S. aquaculture, despite the species’ economic significance and the scale of production. Physical handling during grading and inspection not only causes stress and increased incidence of injury, but also results in unmarketable fish and significant financial loss for producers. To address these issues, we present a prototype system that uses directed water currents to leverage the fish’s natural rheotactic behavior, enabling directed movement between tank regions without the need for direct physical contact. Our design allows for early identification of malformed individuals, who otherwise face prolonged suffering and starvation, so they can be humanely culled. In a small pilot study, we observed that fish moved into the destination region more frequently and with less behavioral variability when exposed to a directed current, suggesting this method as a viable alternative to traditional handling. While the system requires further refinement and testing at scale, these preliminary results offer a promising step toward ethical, commercially viable, and low-stress fish sorting systems in commercial aquaculture.