New publication: Flash photography impacts on fish – To flash or not to flash?

The final paper of my PhD thesis has just been published online in the journal Scientific Reports. The paper, titled “Behavioural and pathomorphological impacts of flash photography on benthic fishes” explains the effects of typical diver behaviour while photographing small critters such as seahorses or frogfishes.

The paper itself can be a tad technical, so with the help of two co-authors (Dr. Ben Saunders and Tanika Shalders), I wrote this summary of the research, which was published first at The Conversation (original article here).


We all enjoy watching animals, whether they’re our own pets, birds in the garden, or elephants on a safari during our holidays. People take pictures during many of these wildlife encounters, but not all of these photographic episodes are harmless.

There is no shortage of stories where the quest for the perfect animal picture results in wildlife harassment. Just taking photos is believed to cause harm in some cases – flash photography is banned in many aquariums as a result.

But it’s not always clear how bright camera flashes affect eyes that are so different from our own. Our latest research, published in Nature Scientific Reports, shows that flash photography does not damage the eyes of seahorses, but touching seahorses and other fish can alter their behaviour.

Look but don’t touch

In the ocean it is often easier to get close to your subject than on land. Slow-moving species such as seahorses rely on camouflage rather than flight responses. This makes it very easy for divers to approach within touching distance of the animals.

Previous research has shown that many divers cannot resist touching animals to encourage them to move so as to get a better shot. Additionally, the high-powered strobes used by keen underwater photographers frequently raise questions about the welfare of the animal being photographed. Do they cause eye damage or even blindness?

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Does flash harm fishes? Photo: Luke Gordon

Aquariums all around the world have taken well-meaning precautionary action. Most of us will have seen the signs that prohibit the use of flash photography.

Similarly, a variety of guidelines and laws exist in the scuba-diving community. In the United Kingdom, flash photography is prohibited around seahorses. Dive centres around the world have guidelines that include prohibiting flash or limiting the number of flashes per fish.

While all these guidelines are well-intended, none are based on scientific research. Proof of any damage is lacking. Our research investigated the effects of flash photography on slow-moving fish using three different experiments.

What our research found

During the first experiment we tested how different fish react to the typical behaviour of scuba-diving photographers. The results showed very clearly that touching has a very strong effect on seahorses, frogfishes and ghost pipefishes. The fish moved much more, either by turning away from the diver, or by swimming away to escape the poorly behaving divers. Flash photography, on the other hand, had no more effect than the presence of a diver simply watching the fishes.

For slow-moving fishes, every extra movement they make means a huge expense of energy. In the wild, seahorses need to hunt almost non-stop due to their primitive digestive system, so frequent interruptions by divers could lead to chronic stress or malnutrition.

The goal of the second experiment was to test how seahorses react to flash without humans present. To do this we kept 36 West Australian seahorses (Hippocampus subelongatus) in the aquarium facility at Curtin University. During the experiment we fed the seahorses with artemia (“sea monkeys”) and tested for changes in their behaviour, including how successful seahorses were at catching their prey while being flashed with underwater camera strobes.

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The aquaria were the seahorses were housed during the experiment

An important caveat to this experiment: the underwater strobes we used were much stronger than the flashes of normal cameras or phones. The strobes were used at maximum strength, which is not usually done while photographing small animals at close range. So our results represent a worst-case scenario that is unlikely to happen in the real world.

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West Australian seahorses (Hippocampus subelongatus) in their aquarium at Curtin University

The conclusive, yet somewhat surprising, result of this experiment was that even the highest flash treatment did not affect the feeding success of the seahorses. “Unflashed” seahorses spent just as much time hunting and catching prey as the flashed seahorses. These results are important, as they show that flashing a seahorse is not likely to change the short-term hunting success (or food intake) of seahorses.

We only observed a difference in the highest flash treatment (four flashes per minute, for ten minutes). Seahorses in this group spent less time resting and sometimes showed “startled” reactions. These reactions looked like the start of an escape reaction, but since the seahorses were in an aquarium, escape was impossible. In the ocean or a large aquarium seahorses would simply move away, which would end the disturbance.

Our last experiment tested if seahorses indeed “go blind” by being exposed to strong flashes. In scientific lingo: we tested if flash photography caused any “pathomorphological” impacts. To do this we euthanised (following strict ethical protocols) some of the unflashed and highly flashed seahorses from the previous experiments. The eyes of the seahorses were then investigated to look for any potential damage.

The results? We found no effects in any of the variables we tested. After more than 4,600 flashes, we can confidently say that the seahorses in our experiments suffered no negative consequences to their visual system.

What this means for scuba divers

A potential explanation as to why flash has no negative impact is the ripple effect caused by sunlight focusing through waves or wavelets on a sunny day. These bands of light are of a very short duration, but very high intensity (up to 100 times stronger than without the ripple effect). Fish living in such conditions would have evolved to deal with such rapidly changing light conditions.

This of course raises the question: would our results be the same for deep-water species? That’s a question for another study, perhaps.

So what does this mean for aquariums and scuba diving? We really should focus on not touching animals, rather than worrying about the flash.

Flash photography does not make seahorses blind or stop them from catching their prey. The strobes we used had a higher intensity than those usually used by aquarium visitors or divers, so it is highly unlikely that normal flashes will cause any damage. Touching, on the other hand, has a big effect on the well-being of marine life, so scuba divers should always keep their hands to themselves.

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Look, take pictures, but don’t touch!


NOTE: I realise that this is a controversial topic in underwater photography. If you have relevant questions, comments, or thoughts you want to share, feel free to add them in the comment section below. If you are interested, I would highly advise you to read the original research paper via this link. The paper is open access, so anyone can read and download it. If you have specific questions about the paper, you can always contact me via email here.

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Keeping seahorses

The last two months I have been running an experiment that involves keeping more than 30 seahorses in aquaria. Not because I am trying to become a marine aquarium expert or because I like seeing fish in tanks. On a personal level I think there are too many environmental issues with aquarium trade to get into it myself. Overfishing of species like Banggai Cardinalfish and Mandarinfish are two examples that come to mind. But this post is not about the aquarium trade, so I will leave those particular issues for another time. While I prefer seeing seahorses in the ocean, for this experiment it was necessary to bring them to the “Curtin Aquatic Research Laboratories” (CARL). This blog explains some of the challenges that come with keeping seahorses healthy in an aquarium. If you are considering ever keeping seahorses yourself, please read this blog carefully.

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West Australian Seahorses (Hippocampus subelongatus) in their artificial seagrass home

DISCLAIMER: This blog describes scientific research, catching seahorses as a private person is NOT allowed in Australia. If you have any questions about keeping seahorses, feel free to contact me in the comments section.

First challenge: Permits. It takes a lots of paperwork to be allowed to do research on seahorses in captivity. Seahorses are on Appendix II of CITES (Convention for International Trade in Endangered Species), which means they cannot be traded internationally if they are smaller than 10cm. But it does not mean that seahorses cannot be fished. As a matter of fact, they are caught in their millions for traditional Chinese medicine! For this experiment it was crucial to use wild-caught West Australian seahorses (Hippocampus subelongatus), which meant applying for permits from the Department of Fisheries and seeking approval from the Department of Parks And Wildlife. Besides government paperwork, doing any kind of research with animals means writing up extensive application (close to 40 pages) for the universities’ ethics committee to ensure proper treatment of the animals while in my care.

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Seahorse tag with red elastomer so it can be identified later

Second challenge: Catching seahorses. As anyone who has ever looked for seahorses can attest to, they are hard to find. There are a few sites around Perth where there are plenty of seahorses to be found, but getting all seahorses from one location would have a huge impact on that particular site. To limit the impact of my collecting, I spread out my fish-catching over multiple sites. To further reduce impact, I did not take any pregnant males or any seahorses that were clearly couples ready to mate. Since I needed a variety of sizes and a similar amount of males and females, collecting enough seahorses took a lot of dives spread out over a few weeks. Once seahorses were caught, they also needed to be transported safely to our facility, which meant not going too far, and using specialised tools to  (sturdy catch bags, coolers, oxygen, etc.) to reduce stress for the animals during transport.

Third challenge: High quality aquaria. Seahorses  are notoriously difficult to keep in tanks. They are very sensitive to bad water quality, which can lead to all kinds of issues. Preparing the aquaria started 6 weeks ahead of catching the seahorses. This is  done to ensure that the biofilters that ensure good water quality get properly established. The tanks themselves need to be large and high enough to house seahorses, and they need hold-fasts that mimic seagrass so the seahorses have something to cling on to.

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First arrivals in the tanks

Seahorses live in salt water, so getting seawater is another issue. Our labs are not directly by the ocean, so we need to import seawater. This then gets sterilised (using UV filters) before we use it. Water quality needs to be monitored daily and adjustments made where needed. This means no weekends off since minor problems could mean dead seahorses. While we have the aquaria and equipment available at CARL, the costs of this would be considerable for a private person.

Fourth challenge: Food. This is probably the biggest challenge of them all. Wild-caught seahorses only eat live food and will not eat dry or frozen fish food. So we need small shrimp to feed them. In our case we are using artemia (= sea monkeys = brine shrimp). Artemia are tiny (less than 1mm) when they hatch, but our seahorses will only eat them when they are about 1cm in size, which means  they have to be grown out for a few weeks before feeding. So we prepared 3 different artemia cultures, each one set up 2 weeks apart to ensure a constant supply of right-sized food. The artemia also need to be fed, in their case with algae. This means 5 cultures of different species of algae to make sure our seahorse-food stayed healthy and fat. Both algae and artemia water quality also need to be monitored, since dead algae/artemia would ultimately mean starving seahorses. To top it off, artemia are not naturally nutritious enough to be the only food source for seahorses. So we added an artemia enrichment-tank (where we add a fatty mix of all nutrients needed for healthy seahorses), which needs to be set up, cleaned, and harvested every day.  The result is that for 3 tanks with seahorses, we have 9 tanks for their food preparation. I’m not sure if you have enough space for that at home?

Fifth challenge: Feeding. As if breeding the food was not hard enough already, feeding them makes it even more complicated. Seahorses have no real stomach to speak of, so they are lousy at digesting their food properly. Because of this they need to eat almost constantly, which is possible in the wild, but harder in an aquarium where too much food will lead to bad water quality. In our case it means feeding them three times per day, every day (bye bye weekends or late nights!). Since our guys have been caught so recently, we can’t just drop the food in the tank and leave it. What works best is hand feeding them with a pipette to make sure they see the food and eat it. Each feeding session takes about 30 minutes, with longer sessions (90 minutes) in the morning, since food has to be harvested first and then a new culture prepared for the next day.

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Feeding the seahorses using a pippette

Sixth challenge: Keeping them healthy. Seahorses kept in aquaria are prone to infections, so besides good water quality  it is important to keep everything clean. This means sterilizing all the equipment we use, only handling seahorses with surgical gloves on, keeping workspaces clean, etc. Regardless of this, infections can still happen. So far I have had to treat one infection with freshwater baths. Earlier this week two males had bubbles in their pouch (common in tank-kept seahorses), which needed to be removed using syringes and gentle pouch-massaging. You read that correctly, my PhD involves giving belly-rubs to seahorses.

All of this is needed just to keep our seahorses alive. I won’t go into what it means to actually run the experiments as well. But if you managed to read this entire post, it should be clear that keeping seahorses means a LOT of work. I am only able to do this because I can use the great facilities at Curtin University and because I have the support of experienced lab technicians, dedicated volunteers, and supervisors with experience in aquaculture. After 2 months of caring for my seahorses, I feel even more strongly than before that seahorses should be in the ocean and not in a small aquarium. If you do want to keep them yourself, think it through before you begin. Make sure you have the right setup BEFORE buying seahorses, only buy captive bred animals and be prepared to sacrifice a lot of your free time for your seahorses.

To finish, here is a short video of one of our seahorses eating artemia: