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A fundamental aspect of assessing the welfare of animals in captivity is to ask whether the animals have what they want. Here, we present a protocol to determine housing preference in the zebrafish (Danio rerio) with respect to the presence/absence of environmental enrichment and access to flowing of water.
Animal welfare assessment techniques try to take into consideration the specific needs and wants of the animal in question. Providing enrichment (the addition of physical objects or conspecifics in the housing environment) is often a way to give captive animals the opportunity to choose who or what they interact with and how they spend their time. A fundamental component of the aquatic environment that is often overlooked in captivity, however, is the ability for the animal to choose to engage in physical exercise. For many animals, including fish, exercise is an important aspect of their life history, and is known to have many health benefits, including positive changes in the brain and behavior. Here we present a method for assessing habitat preferences in captive animals. The protocol could easily be adapted to look at a variety of environmental factors (e.g., gravel versus sand as a substrate, plastic plants versus live plants, low flow versus high flow of water) in different aquatic species, or for use with terrestrial species. Statistical assessment of preference is carried out using Jacob's preference index, which ranks the habitats from -1 (avoidance) to +1 (most preferred). With this information, it can be determined what the animal wants from a welfare perspective, including their preferred location.
The regulations governing how laboratory animals should be housed in captivity are explicit and well-defined. The Association for Assessment and Accreditation of Laboratory Animal Care (AAALAC) International oversees and manages all organizations and institutions that work with research animals and has specific guidelines for species-appropriate husbandry and housing. For example, The AAALAC's Guidance on the Housing and Care of Zebrafish, Danio Rerio1 "strongly encourages" the use of enrichment (the addition of physical objects or conspecifics in the housing environment) when housing zebrafish in captivity. The guide goes on to state, "Providing artificial plants or structures that imitate the zebrafish habitat allow animals a choice within their environment."
Evidence suggests that enrichment can stimulate the growth of new neurons (neurogenesis) in areas of the brain involved in processing spatial information2, and it is thought that these neural changes are associated with enhanced learning ability3. The effects of enrichment on neurogenesis and learning have been widely studied across various taxa, including fish4,5, birds6, reptiles7, and mammals8. Although these types of studies are important to understand the effects of enrichment on the brain and behavior, they do not take into consideration the particular choices or preferences of animals for a particular environment over another.
A fundamental question to ask when assessing the welfare of captive animals is whether or not the animals have what they want9. A way to investigate this question that provides tangible evidence is to provide animals with choices that allow us to understand their subjective preferences. For example, two studies have investigated whether zebrafish prefer access to either an enriched or a plain environment, with both studies indicating a preference for areas that contain enrichment10,11. However, it has also been suggested that zebrafish appear indifferent to environmental enrichment12, so the answer to the question is obviously not clear-cut. Another application of preference testing associated with animal welfare extends to trying to understand how different aspects of an enriched environment play a part in the choices an individual animal makes. In fish alone, different types of enrichment have differential effects on the brain and behavior, and this relationship is further complicated by individual differences in personality traits13. Moreover, preference testing could be useful for comparative studies of environmental enrichment. Even across different fish species, enrichment has been shown to have an effect on many different types of behavior, including aggression14, boldness15, locomotion16, and risk-taking behavior17.
Jacob's preference index is a statistical test that is used frequently to quantify housing preferences18. Jacob's preference index assigns a value to each different habitat based on the number of animals present in each habitat type at different time points, where preference ranges from -1 (avoidance) to +1 (most preferred). Here we describe a method for using Jacob's preference index to investigate housing preferences in fish and use the example of assessing two important characteristics of the aquatic environment: 1) the presence or absence of enrichment; and 2) the flow of water19. However, the protocol could easily be adapted to look at a variety of environmental factors (e.g., gravel versus sand as a substrate, plastic plants versus live plants, low versus high water flow) across different species and landscapes (e.g., aquatic and terrestrial).
The current study has approval and complies with all requirements of the animal care and use protocols of the Pennsylvania State University; IACUC no. 46466.
1. Setup of preference apparatus
2. Capture, acclimation, and procedure
3. Measurements and data analysis
We used the preference test to investigate housing preferences in zebrafish given a choice between varying enrichment including 1) plastic plants and sandy substrate; and 2) water flow. These were divided into four zones: (i) Enriched Only; (ii) Flow Only; (iii) Enriched and Flow; (iv) Plain; and a Central arena where food was delivered19. Zebrafish showed the highest preference for the Enriched and Flow zone, which was significantly different than all other zones (Enriched Only, Flow Only, Plain,...
Here we present an experimental design that allows us to investigate the preferences of fish for different types of habitats. Some critical steps that are important in preference testing include: 1) ensuring that uniform conditions are maintained across different replicates (e.g., external noises or movement, experimenter, water chemistry, light levels); 2) ensuring that the zones are rotated between replicates and a significant amount of water is replaced with fresh sump water between tests to reduce biases; (3) ensurin...
The authors have nothing to disclose.
This work was supported by a Research Collaboration Fellowship and the Huck Institute at The Pennsylvania State University, as well as USDA AES 4558. The research complied with all requirements of the animal care and use protocols of the Pennsylvania State University; IACUC no. 46466.
Name | Company | Catalog Number | Comments |
Artificial Aquarium Plants | Smarlin | B07PDZQ5M5 | |
Artificial Seaweed Water Plants for Aquarium | MyLifeUNIT | PT16L212 | |
Experimental tanks | United State Plastic Corporation | 6106 | |
Floating food ring | SunGrow | B07M6VWH9V | |
Flow meter | YSI | BA1100 | |
Jager Aquarium Thermostat Heater | Ehiem | 3619090 | |
Master Water Quality Test Kit | API | 34 | |
SPSS Statistics for Macintosh | IBM | Version 25.0 | |
Submersible Pump, SL- | Songlong | SL-381 | |
TetraMin Tropical Flakes | Tetra | 16106 | |
Triple Flow Corner Biofilter | Lee's | 13405 | |
Video camera | Coleman | TrekHD CVW16HD | |
Windows Media Player (video software) | Microsoft | Windows Media Player 12 |
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