Inside the Tank: A Peek into the Tecniplast Annual International Zebrafish Husbandry Course, 2023 Part III/III

by Charli Corcoran

The Lectures: top tips and takeaways

The course was rather intense, we had a jam-packed schedule from the course’s start on
Monday evening. It began with an opportunity for networking and to introduce ourselves to
each other and a keynote speech addressing all the amazing things that zebrafish can be
used for in research.  It was a chance for us all to consider what we use zebrafish for in our
own facilities and to potentially think outside the box for ways that we could use the fish in
the future. The rest of the week was a mix of talks and social events that gave us a good
balance of learning and networking. I thought that the topics covered through the week were
a good range, covering the broader aspects of zebrafish care while also focusing on more
specific topics of interest.  

I struggled to choose which lectures to summarise as there were 27 talks throughout the
week, plus a round table event at the end, each talk addressing a different aspect of zebrafish management. I have chosen 7 that I felt were relevant to the wider community.

 Disease and Disease Management
 Health Monitoring
 Water Quality Fundamentals
 “Refinement” and “Setting and Validating Standards”
 Genetic Colony Management
 Enrichment
 Sustainability

Some top tips from Lauren and Justin’s talks were: 

 Understanding the design of our facility and whether it is doing its job properly helps
to mitigate the risk of disease
 Check the efficiency of your UV filter, don’t just assume that it is working properly.
Monitor the flow rate and the UV dose.
 Check your mechanical filters: what is actually getting through?
 Consider work flow and how that can help manage existing pathogen burden
 Colony health management planning is key to controlling your existing pathogenic
burden
 Use an online reporting system that notifies the users about any issues with their fish,
using health indicators and body condition scoring charts.

Health Monitoring
Bruce and Justin discussed health monitoring.  They encouraged us to take the time every
day to observe everything we can about the fish, and to make sure that all staff are trained to
recognise an unhealthy fish.  They talked about the different types of sampling for
diagnostics purposes, and what we should sample: fish, water, biofilms – and encouraged us
to think about what detection, or even lack of detection, of pathogens or microorganisms
might mean.
Key takeaways about Health Monitoring:

 Have a quarantine facility away from the main work room and consider your workflow
 Make decisions beforehand so that it is easier to decide in the moment, and have a
plan for what you will do if your monitoring gets a positive result
 Use sick fish charts and record what you are seeing so you can monitor trends.
Review logs regularly.
 Remove sick fish at earliest opportunity
 Investigate mortalities that shouldn’t have occurred
 Fecundity monitoring can be an early indicator for any problems.

Water Quality Fundamentals
This was one of the presentations that I was looking forward to going into the course, as
some areas of water quality continue to be a challenge for our facility. I was keen to hear
what Karen had to say on the topic and to discuss our concerns with other zebrafish people. 
Karen’s talk addressed the impact of water parameters on zebrafish welfare. Water
parameters have a complex relationship with each other and it was good to relate some of
those with some potential welfare issues that we might see in our fish.
Some of Karen’s Water Quality dos and don’ts:

 Zebrafish can tolerate a wide range of environmental conditions but they do not
tolerate sharp changes so acclimate your fish to any changes slowly 
 Remove chlorine using carbon filters

Water Hardness
 Low alkalinity can increase the toxicity of dissolved metals
 The recommended range for zebrafish is 50-75ppm
 Soft water (<60ppm) results in difficulties maintaining egg supply or survival

pH
 Haemoglobins affinity for oxygen decreases as pH decreases
 Nitrogenous waste is more toxic at high pH levels
 Zebrafish can tolerate a wide range 

Temperature
 Higher temperatures speed up development and aging and also food
consumption
 Activity and behaviour are highly affected by temperature
 Toxicity of nitrogenous waste increases with temperature
 Dissolved oxygen decreases as temperature increases
 Chlorine and Chloramines
 Low levels of chlorine cause stress and irritated gills
 High levels are fatal

Water Flow
 High water flow is good for adult fish, high occupancy tanks, tanks in rooms
with low ambient temperatures and tanks getting a lot of food. 
 Low water flow good for younger fish and for blind fish

Static Tanks
  Check water quality of static tanks regularly
 Change water regularly

Refinement and Setting and Validating standards.
Carrie’s talk on refinement in zebrafish, and Lauren’s talk on setting and validating
standards, were very motivating, encouraging us to make the small changes and
refinements that can be implemented at a local level, to do the validation studies, to publish
the results, and apply it from a facility management perspective.  

Key messages from the refinement and setting and validating standards presentations:

 We can be so focused on trying to make big changes, that we overlook the small
improvements that we can make at a local level in our own facilities.
 Small changes can lead to improvements in welfare
 Start by asking the question “Why do you do it that way?”

 Validate your changes and publish any results: Zebrafish Journal* would be a good
place to start with publishing any results.
 Always assess the ‘new thing’ that you heard at the conference with what works in
your facility and with your users

*I did not know about the Zebrafish journal, here is a link for anyone like me:
https://www.liebertpub.com/loi/zeb.  

Genetic Colony Management of Zebrafish 

This session was of interest to many of the attendees, and Karin focused on things to
consider in preventing and identifying phenomena such as inbreeding depression and the
founder effect in our zebrafish colonies.  She also linked good genetic health with the 3Rs:
how developing methods that focus on high survival is a good way to minimise the number
of animals used (Reduce), and she discussed methods to maintain good genetic diversity in
our wildtype stocks.

Some of the key messages from Karin’s talk on genetic colony management are:

Enrichment 
Enrichment is another topic that we are discussing a lot in our facility at the moment, and a
topic which some of our undergraduate students are in the process of looking into, so I was
really interested in this session, and to hear the speakers and attendees’ views on
enrichment in zebrafish facilities. Karin defined enrichment as additions or modifications to
the basic laboratory environment which aim to improve laboratory animal welfare. She talked
about the benefits and objections, and the different types of enrichment that we might
encounter in our facilities.
Top Enrichment tips: 

 Enrichment is not one size fits all: consider age, group size and sex
 Habituation can lead to lack of interest, so change enrichment frequently
 Simple tank changes can improve welfare
 Communicate changes with staff and users

Sustainability in a Fish Facility
I was looking forward to this session as sustainability is a topic that’s heavily discussed in
the wider environment of our institute.  I think it can be quite overwhelming to think about
how we can be more sustainable in a facility where the large majority of our equipment has
to be running all the time.  This session was a little different to the rest of the week, as we
divided up into small groups and separated out to discuss the ways which we have been
able to be more sustainable in our own facilities, and share ideas to help others take steps to
be more sustainable.  

Obviously not all the ideas and solutions will be viable in all facilities, but having that time to
discuss in a group and hear how things had worked out in different facilities around the world
was very useful.

Some of those ideas: 
 Adjust feeding regime to reduce required cleaning and filter changes and to reduce
food waste.
 Look at ways we can reduce our consumable use: wash the filter mats in hot water
instead of replacing them every time, and clean petri dishes in a bleach solution.  In
this particular case, washing the petri dishes had cut down on petri dish purchase by
90%.  Biodegradable petri dishes were also suggested, as was the use of glass petri
dishes.
 Adjusting water exchange when the total system volume changes to make sure that
water is not being wasted.
 Recycling the water that we use.

I really enjoyed the format of this session and I do wish there had been other opportunities to
discuss specific topics in more formal settings like this throughout the course.

I fully agree with Michaels point that a lot of the things that were discussed on the course
were things that many of us already knew, but didn’t really have any ways of enforcing in our
facilities or with our users.  The course empowers us to enforce those things by sharing
some of the consequences of not enforcing those steps.

Each presentation had time for discussion afterwards. These were sometimes lively
opportunities to ask specific questions which had come up during the course and it was
really great to hear all the questions that the attendees had. 

“I gained a lot of insights and useful information through sharing my challenges.”
-Iris Y.K. Woo, University of Hong Kong

Like Iris, I found these discussion times helpful, as well as the more informal networking at
lunch or during the social time.  I found it helpful to be able to hear about issues that other
facilities had encountered, as there is always the potential for those problems to crop up for
me in the future. There was also the opportunity to write down any questions or topics for
discussion, and put them in the fish tank. A round table was held at the end of the week,
where the panel of speakers answered or discussed the questions that had been left in the
tank. This was a fantastic opportunity to get expert opinions on any zebrafish related topics.