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Third R&D Study of 2024: Dissolved Oxygen Tolerance Assessment

By Dr. Paul Monaghan, Fish Welfare Initiative Research & Development Lead


Summary

Dissolved oxygen (DO) is considered the key water quality parameter by FWI, and many corrective actions recommended to farmers by FWI are based on DO levels. Few studies have been conducted to determine the oxygen requirements of Indian major carps (IMCs), the primary beneficiaries of FWI in India. Given the sparsity of published data about IMCs, we seek greater confidence for the DO ranges we apply as a proxy for fish welfare. We also seek greater confidence for acceptable tolerance levels of ammonia. This post discusses a study that we began today, and which will run for the next two months at our new test facility, to understand the levels of DO and ammonia which IMCs can tolerate without exhibiting welfare concerns.


In order to improve its programming, FWI is investing more in R&D this year. We will be running several studies throughout the course of the year in order to inform improvements to our programming, and will keep our blog updated with our progress.


Background

FWI’s core program, the Alliance for Responsible Aquaculture (ARA), focuses on improving water quality in fish farms. This program centers on our ground teams collecting water quality data from farms and providing the farmers with corrective actions in the event of key water quality parameters indicating that fishes may be exposed to poor conditions. Dissolved oxygen (DO) is considered the key water quality parameter by FWI, and many decisions by FWI around fish welfare are based on DO levels. ARA ground teams issue corrective actions to farmers when DO is outside of FWI’s recommended range of 3-5 mg/L (based on measurements taken in the morning). 


Indian major carp (IMCs)—the primary fishes targeted by FWI in India—are considered quite tolerant to DO compared to many other fishes, but few studies have been conducted to determine their oxygen requirements. Given the sparsity of published data about IMCs and how they are or are not impacted by specific water quality parameters—in particular, DO—is FWI confident in the recommended DO range that it has set?


As FWI aspires to be an evidence-based organization, the evidence for the DO range utilized for decision-making needs to be strengthened. To generate this evidence, FWI is conducting a study to understand the levels of DO which IMCs can tolerate without welfare concerns.


Additionally, this study will be looking at tolerable levels of ammonia. Ammonia is known to impact DO levels in water, and a recent study by FWI suggests that the combination of ammonia and DO may be a more important indicator of fish welfare than DO alone. A study that takes into account the dynamics of water quality, particularly the interplay of DO and ammonia, would help us understand if DO on its own is a suitable proxy for fish welfare, and/or if there is a need to refine the water quality conditions—specifically, the combination of DO and ammonia levels—which should trigger our decisions to recommend corrective actions to farmers.


Hypothesis

If we conduct laboratory-based experiments to ascertain the DO levels which IMCs can tolerate without welfare concerns, we would obtain empirical data to inform if FWI’s focus on DO is justified, or needs to be reconsidered. If it confirms that DO is a justified concern, the study would inform the lowest level of DO at which corrective actions should be issued as part of the ARA, and how ammonia can be factored into this decision-making.


Research Question

We have two research questions with this study:


  1. What is the lowest level of DO which IMCs can tolerate without exhibiting welfare concerns?

  2. How does DO tolerance for IMCs change with varying levels of ammonia?


Our Plans

On this post’s date of publication, July 10, we have initiated a study to provide empirical evidence to inform our decisions around the need to refine the water quality conditions—specifically, the combination of DO and ammonia levels—which should trigger our decisions to recommend corrective actions to farmers.


Due to the requirement to carefully control parameters—namely, DO and ammonia—this study is being conducted in a laboratory setting, not in aquaculture ponds. We are conducting this study in our custom-built test facilities hosted at our university partner Adikavi Nannaya University (AKNU) in Rajamahendravaram, Andhra Pradesh. Last year we constructed six test ponds in collaboration with AKNU in order to enable us to test different practices in controlled, farm-like conditions (we have recently initiated a study to test fortified feed in these test ponds). We recently expanded this test facility to include a laboratory housing a number of tanks to allow us conduct experiments that require even more refined control of environmental conditions than is possible in a pond.


Our purpose-built laboratory facility where we will conduct the study houses eight tanks. Six 500 L tanks (background) will be used for experimental conditions. Two larger 1500 L tanks (foreground) will be maintained at optimal water conditions for fishes, into which fishes will be moved once they exhibit stress in the smaller experimental tanks.

The study will utilize six 500 L tanks, three for experimental conditions and three for controls. The study will be conducted in phases over the course of a approximately two months:

  • The first phase—designed to determine the lowest level of DO which IMCs can tolerate without exhibiting welfare issues—will involve slowly and incrementally reducing the DO levels in experimental tanks, while keeping the DO levels constant in the control tanks. 

  • The second phase—designed to determine how IMC’s tolerance for DO changes with varying levels of ammonia—will involve keeping DO constant (at the lowest tolerated levels identified through the first phase), but slowly and incrementally increasing the levels of ammonia in experimental tanks, while keeping the ammonia levels constant in the control tanks.


Data, including water quality parameters and welfare indicators, will be collected throughout. Fishes will be carefully and constantly monitored throughout the study, and will be transferred to a tank with more optimal conditions once data indicates they are stressed. Beyond the stress they experience from exposure to low DO levels, no fishes will be intentionally harmed or killed in or after the study. After the conclusion of the study, the fishes will be released into the nearby Godavari River (we have obtained permission from local authorities for this wild release). The study protocol has received ethical approval from AKNU’s Institutional Ethical Committee.


The study will be conducted over the course of a number of weeks. Time is required to allow fishes to acclimate to the tanks before starting each phase of the study. All phases of the study are expected to be finalized by the end of August, with preliminary results expected in September.


We’re conducting this study in keeping with our commitment to evidence-based decision making. Regardless of the results, the data from this study will inform our programming—data may indicate that our existing DO thresholds are correct, or need to be changed. Either way, the study will provide critically important information to guide FWI’s decision-making.


We’re excited to commence this study, and look forward to how the results will inform our programming. As we intend to publish this study in a peer-reviewed journal, full sharing of results isn't expected until next year in line with publication of the paper, but we will endeavor to share updates later in the year.



Our newly-constructed laboratory facility where we’ll conduct the study (dark blue building on the left of the image) is part of our custom-built test facilities at Adikavi Nannaya University, which also includes six test ponds.

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