Freshwater ecosystems (eg rivers) are being rapidly degraded, leading to a sharp decline in fish populations (eg up to 93% in Europe over the approx. the last 50 years). Numerous human activities are driving this decline (e.g. pollution, invasive non-native species, construction of river infrastructure such as dams, weirs and culverts) and in turn a wealth of lab-based research, utilizing live fish, aims to understand and provide information that can help mitigate (or lower) impacts, particularly those that affect important aspects of behaviour. It is important that the information obtained from this research is reliable and transferable to the applied problems being investigated, and assumes the animals are in a good welfare state and exhibiting natural behaviours in response to the factors being investigated.

Structural environmental enrichment (EE) is an important aspect of the fish husbandry environment. For example, fish from enriched (vs. barren) husbandry environments can demonstrate greater rates of recovery from handling, cognitive abilities that enhance agility and lower behavioural variability during experiments in novel environments. EE therefore has important implications for fish welfare but also potentially the results of applied lab-based behavioural research. However, EE is poorly documented in scientific publications, and its provision varies substantially between research groups and thus studies. This is problematic for a number of reasons. Firstly, it makes it almost impossible to precisely replicate most experiments as this should include the husbandry environment. Secondly, variability in the provision of EE in husbandry tanks within and / or between studies could be influencing experimental results in unknown ways.

In this project, the interplay between preferred EE, welfare, and behaviour was explored during a fish passage study. The results would add to a limited evidence base, helping decision making in relation of provision of EE, specifically for researchers, aquarium technicians or others in charge with overseeing the husbandry and care of fish housed for behavioural studies. Secondly, outputs are hoped to encourage researchers to more thoroughly consider and report the husbandry environment (e.g. in scientific publications), leading to better welfare for fish used in behavioural research and improving experimental replication (and ultimately the robustness of the science we do with fish). 

The study was run without any difficulties encountered, but a decision was made early to analyse the fish preference video data in a much more detailed way than originally planned. As such, the data analysis for this element is still on-going and will form the basis for a second publication. This approach will maximise the benefits and outputs from the data collected.

Presentations and publications:

Vowles AS (2025) Environmental enrichment as a confounding variable in applied behaviour research. UFAW International Animal Welfare Conference, 24-26 June 2025, online.

Vowles AS & Currie H (2025) Environmental enrichment in the husbandry environment as a confounding variable in applied fish behaviour research. Fisheries Society of the British Isles Annual Conference, 7-11 July 2025, Belfast, Northern Ireland.

Vowles AS (2025) Physical environmental enrichment as a confounding variable in fish behavioural research. CABI Animal Behaviour and Welfare Cases, https://doi.org/10.1079/abwcases.2025.0017