Welfare insights
Two prize-winning studies by Swansea University students offer a new perspective on fish and shrimp welfare.
CSAR, the Centre for Sustainable Aquatic Research at Swansea University, is one of the UK’s leading centres of academic excellence in its field. This year, three Swansea students have been recognised for their dissertations in the centre’s annual awards.
Charlotte (“Lottie”) Oulton and Oliver (“Ollie”) Duke won a joint award for the Best Welfare in Aquaculture Dissertation, with a study showing how providing a choice of feed can improve welfare for farmed tilapia.
Jack Van Eker was awarded Best Aquaculture Dissertation for his study of farmed shrimp and their temperature preferences.
These two awards were sponsored by Fish Farmer magazine as media sponsor, and the Best Welfare in Aquaculture award was sponsored by animal welfare certification body RSPCA Assured.
Also, Edwin Batchelor’s report comparing the welfare, growth and feed conversion rate of tilapia reared for four weeks with three different feeding systems (on-demand, pulse and continuous) was declared the winner in the Best Aquaculture Practical Report.
“The shuttle box allowed individuals to express their temperature preference”
Development of measures of positive welfare for Nile tilapia
Charlotte Oulton & Oliver Duke
Most current welfare measures for farmed fish focus on reducing or eliminating negative impacts on an animal’s wellbeing. However, fish can also access positive experiences that traditional welfare measures ignore.
The premise of the study was that giving fish a choice of food, and when and how much they eat could bring back a feeling of freedom of choice, increasing positive welfare.
Nile tilapia (Oreochromis niloticus) is one of the most farmed fish worldwide, but little is known about its positive welfare needs.
The starting hypothesis was that fish housed in the “choice tanks” would demonstrate better welfare-linked behaviours, such as boldness and curiosity, than fish in the “no-choice” tanks.
This study addressed this knowledge gap by investigating the potential for dietary choice to improve positive welfare of farmed Nile tilapia.
Sixty juvenile Nile tilapia were reared in duplicate tanks and fed using on-demand pendulum feeders over a six-week period. The on-demand feeders allowed the Nile tilapia to dispense food upon contact with the pendulum.
One group had a choice of two different diets in each feeder (dietary choice), while the other groups had the same diet in each feeder (no dietary choice). All diets used had similar nutritional values.
The Nile tilapia’s behaviour (number of aggressive interactions and interactions with the feeders) was recorded over six weeks, and some behavioural welfare metrics (boldness, neophobia and thigmotaxis, that is response to physical contact) were recorded for individual fish at the end of the trial.
Given a choice of diet, Nile tilapia showed evidence of higher levels of boldness, lower anxiety around a novel object and demonstrated less aggression. However, other welfare metrics were not affected by choice.
The findings from this study suggest that dietary choice can alter affective states that might improve fish welfare in an artificial environment, allowing the expression of more natural behaviours. Dietary choice, say Oulton and Duke, can open a promising avenue for introducing measures of positive welfare on farmed fish.
Charlotte (“Lottie”) Oulton said: “The thought of studying something that can improve the lives of animals that don’t have a say as to how they are reared (like fish in aquaculture) really intrigued me and the thought of possibly making a difference to these animals was appealing.
Also, the opportunity to work with someone like Professor Garcia de Leaniz [CSAR Director] and the other professionals within the CSAR facility was exciting.”
She added that rearing the tilapia from fry, and building the rotating metal rig for feeding, were the most enjoyable parts of the project, while the most challenging was working in the lab at a constant temperature of 32C.
Oliver (“Ollie”) Duke commented: “The entirety of this research project was fun, but most elements were challenging, primarily because I had never looked after 120 Nile tilapia before! Aside from the challenges of learning the husbandry behind rearing our Nile tilapia, I also learned how to handle new (and exciting) data and engineer our experiment set-ups. All these things were challenging and fun at the same time.”
He added: “This research makes me want to continue improving my academic skills to conduct better research in relevant fields that need change.”
Emilie Wix, Head of Farming Engagement at RSPCA Assured, said “We are delighted to again support these excellent fish welfare projects undertaken by the students at Swansea University. Farmed fish welfare is an important issue and we hope that by sponsoring awards such as this, we can help to encourage the fish industry specialists of tomorrow to prioritise improving welfare standards.
“We are proud that the RSPCA Assured scheme and the RSPCA higher welfare standards for farmed Atlantic salmon and trout have been a catalyst for change for over the last 20 years, and we look forward to seeing what Lottie and Ollie do next.”
Tilapia test arena with unfamiliar object
Some like it hot: Assessing temperature preference in white leg shrimp (Litopenaeus vannamei)
Jack Van Eker
Despite the popularity of white leg shrimp (Litopenaeus vannamei) as a farmed species, the paucity of scientific research information regarding its environmental preferences has been detrimental to welfare efforts that would improve the health and well-being of individuals.
This study used a shuttle box to assess temperature preference in L. vannamei, which allows individuals to dynamically regulate temperature – a method that has yet to be used in this species.
The shuttle box comprises two sub-chambers connected by a passageway that allows an individual to “shuttle” between increasing or decreasing water temperatures without the water mixing. An overhead camera detects the position of the shrimp, and either warmer or cooler water is pumped into the chamber to force it to make a new choice. The maximum tested temperature was 33°C and the minimum 20°C (based on existing information) and the rate of temperature change was set to +/-2°C per hour.
In total, 30 freshwater post-larvae were monitored individually over 24 hours. They were measured and weighted in resealable plastic bags filled with water to reduce stress, and three thermal values were obtained: preferred temperature, upper avoidance temperature, and lower avoidance temperature.
White leg shrimp larvae being measured
Results indicated an optimal thermal range for L. vannamei between 29.16°C and 32.83°C (figure 2) with smaller individuals displaying a significant preference for warmer temperatures, and larger individuals showing significantly higher variation.
This is warmer than the lower temperature commonly used in RAS-based shrimp farms (25.5 C). Increasing the current low rearing temperature by 3-4°C should improve welfare by preventing thermal stress, which this study suggests may begin at temperatures below 29 C.
Maintaining temperatures above the lower avoidance threshold of 29C appears to be particularly important for post-larvae below 8g, as they prefer warmer waters, becoming more cold-tolerant as they grow.
Studies like these will help provide valuable insight into the physiological and behavioural responses of L. vannamei to changing environmental conditions and inform welfare guidelines to help facilitate sustainable aquaculture practices.
Jack van Eker commented: “The practical part of the research like problem solving and fixing machinery was fun. The data analysis was probably the most challenging part of the work, namely because of how large the dataset was and how much my laptop hates larger files.”
He added that among the main takeaways from the project were: “The importance of a holistic approach to research; to consider ecology, behavioural changes, and an individual’s preference.”
