That Fish Blog – Aquarium Advice and Information
Mudskippers, the largest species of which reach a length of 12 inches, inhabit tidal flats, river mouths and mangrove swamps in East Africa, Southeast Asia, Australia, and along the Red Sea.
Gill covers tightly seal the gill chambers, and water stored there keeps the gills moist and provides oxygen to the fish as it scuttles about on land. Mudskippers also absorb moisture from the damp mud upon which they usually travel when out of water. Although it is tempting to think of mudskippers as representing an early stage in the development of amphibians, the creature that gave rise to frogs and salamanders was more like the Australian lungfish, Neoceratodus fosteri, in appearance and in its method of breathing (utilizing primitive lungs).
The most commonly available mudskipper in the pet trade is Periopthalmus barbarus, a fairly hardy species that reaches a length of 6 inches. Like all mudskippers, it hails from brackish water areas.
Mudskippers are fairly tolerant in their salinity requirements, and will do well under typical brackish water aquarium conditions (salinity of 1.005-1.015) and temperatures of 75 – 80F. They require a “beach” area, which can be a separate, drainable plastic container within the main aquarium or designed as small islands fashioned from non-toxic tree roots, coral heads and rocks. The popular “aqua-terrariums” now on the market make excellent mudskipper homes as well. Remember to keep the water shallow, or to provide easy access to land, as they are poor swimmers (not something you usually worry about when keeping fish!).
Most mudskippers do well in captivity if provided with a suitable habitat. Males, however – distinguished by their large dorsal fins and bright colors – are very territorial, and dominant specimens will make life miserable for others, so plan your group and space accordingly.
Although they prey upon live invertebrates such as crabs and insects in the wild, mudskippers adjust well to frozen foods such as prawn and clams. I also provide a vegetable-based frozen food from time to time, and find they accept this readily as well. Their food should be placed on land, as most species will not feed while submerged. Mudskippers are especially fond of live crickets, small shrimp and other such foods, and these should form a large portion of their diet. Their acrobatics when chasing live food – they often flip over in their excitement – never fail to delight me.
Brackish water community tanks containing mudskippers and fiddler crabs make fascinating exhibits. The interactions between the crabs and mudskippers (assuming they are properly matched in size!) go on all day long. If you establish a deep water area (mudskippers will do okay as long as they can exit the water easily) you can add such fascinating fishes as four-eyed fish, Anableps spp., scats, Scatophagus argus and rubrifus, monos, Monodactylus argenteus, and, of course, the amazing archer fish, Toxotes chatareus. In fact, archer fish are at their best in an aquarium containing a land area because in such they can show off their incredible ability to knock crickets from land into water. Somehow compensating for the refraction of light through water, archerfish eject streams of water at insects (best observed by placing crickets on branches positioned over the water’s surface), hitting them unerringly and thus securing a meal. They will also aim water at your eye movements, so be careful!
I’ll cover the creation of such aquariums in future articles. Until then, please share your observations and write in with your questions. Thanks, Frank.
For more information on establishing aquariums for brackish water fish, please see the article Brackish Water Basics, posted on on February 26, 2008:
Hi,
I have several mudskippers in a 55 gallon brackish water tank. Their land area is driftwood. I plan to switch to mud once I have the time to set it up properly. In the water portion of the aquarium I keep glass fish and puffers. I often see fiddler crabs for sale, I know some species live with mudskippers in nature and was wondering if they would coexist in a tank? Also your article mentions Australian lungfish. I’m very interested in unusual fish and would like to look into keeping these. Are they ever sold, and do they have special requirements? I’ve seen large lungfish, I think African, at the old Steinhart Aq. in San Francisco, very impressive. Thank you.
Hello,
Frank Indiviglio here. Thanks for your interest in our blog.
The key to keeping mudskippers with fiddler crabs is space…I was able to it in an exhibit with an area of appx. 3’ x 3’, but in a 55 gallon set-up it was difficult – the mudskippers charged the crabs each time they emerged from the water. The crabs did fine, but mainly remained in the water, coming onto land in the evening. You might try it once you have set up a mud substrate – in this situation the crabs will establish burrows, so the usable space within the aquarium will be increased. Most fiddlers sold in the trade are held in fresh water…be sure to adjust yours to brackish water slowly.
Lungfishes become great pets, with captive longevities approaching 30 years. Most available in the pet trade are 6-10 inch long juvenile West African Lungfish, Protopterus annectans annectans. They eventually reach 3 feet in length and are very forgiving re water quality, but should none the less be kept as you would any other tropical fish. They are escape artists, and almost always intolerant of any tank mates, even similarly sized lungfish. Please let me know if you decide to keep one, and I’ll send along specific care information. The Australian species is an incredible beast, but unfortunately never available in the trade. I have seen them in aquariums in Japan (where part of their diet is plantain chunks!), but not in the US.
Steinhart was a wonderful place, wasn’t it? I have not seen it since the renovations, but they were known for their unique assortment of very large and long-lived individuals of many fish species. You can also see lungfishes at the NY Aquarium…and I recently set up an exhibit for them at the Maritime Aquarium in CT.
Best regards, Frank Indiviglio.
Hello, since I wrote last I purchased a small lungfish… the pet store fed it only goldfish which is not great as a sole diet I know, they do not have much of a variety of dry foods, are there any I can order or buy somewhere that the lungfish would accept? Also i feed my mudskippers mostly crickets, which they love, but would like to add variety, anything else they would eat? Thanks.
Hello,
Frank Indiviglio here. Thanks for your interest in our blog.
You are correct in seeking to provide a more varied diet for your fishes…goldfish as a sole diet are particularly bad.
We carry a number of foods that will round out your lungfish and mudskipper’s diets. Please click on the links to see product details.
Lungfish readily accept frozen, freeze-dried and pelleted meat-based foods; yours may take a little time to adjust as it was given live foods only. Introduce them slowly, and keep him a bit hungry at first…as you know, lungfishes are great at storing away food (aestivating animals have gone 4 years without!), so don’t worry if he skips a few days.
Ideally, you should alternate between 2 or more of the following, and offer minnows, shiners, crickets, waxworms and earthworms as well:
Pellets
Hikari Massivore Diet, Sinking Carnivore Pellets, Cichlid Staple
That Fish Place Shrimp Pellets
Freeze Dried
San Francisco Bay Krill
Frozen
San Francisco Bay Frozen Beefheart
San Francisco Bay Silversides, and other marine foods (i.e. squid, mussels) can be used once each month or so as a treat.
I’ve found that mudskippers accept a wide variety of pelleted, freeze dried foods if these are moistened, but are especially fond of frozen foods. I always mix in a product with some vegetable material, as they seem to take in algae etc. in the wild, possibly when swallowing mud along with live insects (?). In any event, mine have done well for years on a diet composed of live and frozen/other food.
Frozen/dry foods should be placed on a plastic jar lid or similar surface for ease in cleaning up leftovers.
Frozen
San Francisco Salt Water Multipac Roll a Cube is ideal, as it contains a wide variety of different ingredients, including algae-based foods.
San Francisco Bay Emerald Entrée Cubes
Pellets
Any listed for lungfish: mudskippers especially favor Shrimp Pellets
Freeze Dried
San Francisco Bay Freeze Dried Bloodworms, Ocean Plankton, Daphnia, Brine Shrimp
Please let me know if you need anything further, good luck!
Best regards, Frank Indiviglio.
Hello,
I have fiddler crabs in with mudskippers (I wrote before), and they seem to be getting along The crabs are always picking at the wood when out of water, and in the gravel underwater, but I’m not sure how much food they are getting. The fish eat everything pretty quickly. Is there an effective way to feed the crabs? Thank you.
Hello, Frank Indiviglio here. Thanks for your interest in our blog.
Good question – fish usually out-compete invertebrates, so it’s important that you give thought to this topic. Fiddler crabs will eat underwater, but feed most effectively on land. You can limit the food taken by the mudskippers if you feed the crabs just before shutting the aquarium light for the evening. If you prefer to feed in the day, grind the food up into very tiny particles…the crabs’ feeding claws (the smaller set on the males) are tiny, and they actually prefer minute food particles. Such would likely not interest the mudskippers. Another method is to use Tetramin Tablets or other food items that might be too large for the mudskippers to swallow – just be sure to moisten these so the crabs can pick at them easily.
If the mudskippers harass the crabs on land, you can feed them underwater. I believe you mentioned having glass fish and other species in a past note, however…if this is the case, feed the crabs underwater at night, and use tablets that dissolve slowly.
I hope this proves useful…please let me know if you need further information.
Best regards, Frank Indiviglio.
Hey there! I have a quick question for you. I am looking into starting up an aquarium again and I would like to get some mudskippers. What is the ideal tank and setup (habitat) for two or three? What gallonage am I looking at needing? Thanks!
Hello, Frank Indiviglio here. Thanks for your interest in our blog.
The most commonly available mudskipper species, Periopthalmus barbarus, reaches 6 inches in length. Three could be housed comfortably in a 15 gallon aquarium.
In a 15 gallon aquarium, a simple habitat can be arranged by using a Zoo Med Turtle Dock as the land area. It slopes nicely, allowing the fish easy access. Mopani Wood arranged to protrude above the water’s surface works well also.
In a larger aquarium, you might consider creating a mud or sand “beach”…please see details in the article or write back if you’d like to consider this option.
The best filtration method to choose will depend on your water depth and tank size – once you have decided, please be back in contact and I’ll provide some suggestions.
Good luck on your new venture – mudskippers are great fun and very interesting…enjoy!
Best regards, Frank Indiviglio.
Hi I also want to keep mudskippers but i dont know where to find them, do you know of any websites that sell them?
I have 2 mudskippers in a 20L and they seem to be doing great. They recently destroyed their ‘scaping by digging burrows in the sand part. I have an idea to make it more stable that I will be setting up this weekend. My question is, one of them is very aggressive, first to the food,(and biting my fingers)first to burrow, and first to great me when I get home. It totally dominates the other one. Is it possible that I have a female and a male?
Hello Jacki, Frank Indiviglio here.
Thanks for your interest in our blog. It sounds as though you are doing very well with mudskippers…congratulations, they can be tricky.
It could very well be that you have a pair. If they are full grown (5-6 inches for the most commonly imported species) then the male will have a noticeably higher dorsal fin, and he will be brighter in color – bright blue dots will be especially numerous.
However, in large groups I have seen females dominate other females, mature males chasing immature males, and so forth, so there really seem to be no general rules.
Sight barriers, in the form of driftwood, artificial plants or elevated sand banks are often effective in reducing aggression.
Please keep me posted, and let me know if you need any further information.
Best regards, Frank Indiviglio.
I have search every for this little guys an I have had no luck find them. any idea where i could pick two or three up
There was a time when they were much more common, but in recent years their availability has decreased. I recommend you search forums for people who have them mand may be interested in selling of trading, I do not know of a present source.
Hello,
I currently have a 46 bowfront tank that I want to setup for a mudskipper tank and was wondering how many I could realistically fit in there (I was hoping 4-6)? Also, I’ve been trying to do as much research as possible but nobody had a definite answer for filtration for the tank. My original thoughts were a sponge or a waterfall filter. My last question is do the mudskippers need mud or would some type of clay work just as well?
Hello, Frank Indiviglio here. Thanks for your interest in our blog.
Your tank will make for a very interesting mudskipper exhibit. The safest route would be to go with 1 male and 4-5 females, assuming that you keep the most commonly available species, Periopthalmus barbarus and that a substantial portion of the tank is set up as a beach. If the land area is broken up a bit by water and sight barriers, it might be possible to house 2 males and 4-5 females; this makes for interesting displays between the males, but you would need to have another tank set up in case the males become too aggressive towards one another.
Several larger species occasionally enter the trade – for these, I suggest 1 male and 2 females.
A canister filter set up with a waterfall style return would work out well, as would an undergravel filter or possibly a sponge filter as you suggest (especially if the water volume is small.
Mudskippers do not tax the water, in terms of ammonia etc., as much as they do the beach area…however, if the beach area drains into the water then water quality is more of a concern. You won’t be able to filter through the beach area. The ideal situation would be to have a separate area for the beach – a container, another tank or a beach created by using silicone to attach glass panes to the bottom and sides of the aquarium. A rubber-stopped hole cut into the bottom of the beach container (I use glaziers for cutting into aquarium glass, but some folks do this on their own) would allow for drainage and prevent the substrate from becoming foul.
Another option would be to plant live mangrove seedlings in the beach area. These are often available from dealers in Florida, add a nice touch to the tank, and do a great job in keeping the beach area clean and fresh. If the substrate is limited to 2-6 inches in depth, periodic replacement of the top layers would work well also.
As concerns the substrate, I would not recommend clay, as it compacts easily, and has no buffering capacity; I’m also not sure about its over-all effect on water chemistry in a brackish/marine aquarium. I have used mud collected from salt marshes, but this takes a great deal of management, and also compacts readily, creating a prime habitat for anaerobic bacteria. Many of the tiny invertebrates that live within the mud die off once transferred to an aquarium, causing additional problems.
I suggest Seachem Onyx Sand Gravel as a beach substrate. It is porous, helps maintain an appropriate pH and supports plant growth. Its color evokes that of mud, imparting a naturalistic appearance to your tank while dispensing with the concerns associated with the real thing. I would also mix in (20-30% by volume) some Koralagoon Aragonite Substrate . This product helps support the natural biological reactions that occur in estuarine environments, and is especially useful in maintaining substrates planted with live mangrove seedlings.
Sounds like a very interesting project…good luck and please keep me posted.
Best regards, Frank Indiviglio.
Hello Frank,
Thanks for the reply. I really appreciate the tips and suggestions you have given me and you pushed me over the edge into getting the mangrove seedlings.
I’ve heard different stories about raising mangroves that no matter what they will eventually grow out of the tank constraints but is there a way around this perhaps by pruning the plant frequently?
I have one other question before I actually start the endeavour of starting the tank setup. I have an interest in trying to breed the mudskippers to try to make some money back for the setup because it is becoming expensive. I was wondering if you have had any experiences with this or maybe and helpful hints that might help out because I have heard that this is sometimes extremely difficult in captivity. Thanks for all your help.
Hello, Frank Indiviglio here. Thanks for your kind comments and feedback.
I had one situation in which mangrove shoots stabilized at about 12 inches in height…it was a tall zoo exhibit and I believe the light intensity was a big factor, but I do not have detailed notes. If given adequate lighting, however, the do grow rapidly and will need pruning.
Unfortunately, mudskippers have proven impossible to breed in captivity, even in large public aquariums. A good deal of work has been done in several aquariums in Japan, but as yet without success. Like most fishes and invertebrates that live in estuaries, mudskipper reproduction is heavily influenced by tidal cycles and changes in salinity and other water quality parameters. They also must be able to establish sufficiently large territories, and to construct a deep chamber for the eggs. The eggs themselves are exposed to extreme temperature/salinity changes during development (in some species the female aerates the eggs) and may need such in captivity. Upon hatching, the fry utilize a different habitat than do the adults.
This is not to say it cannot be done…if you have an interest, by all means go to it. Whatever you learn would be of great value to others.
Good luck and please keep me posted.
Best regards, Frank Indiviglio.
Hello again Frank,
Well I’m finally about to purchase my little mudskippers and I was wondering if you could help me out with figuring out which species of mudskipper im purchasing. When I went to my LFS the owner said they are vietmanese mudskippers and they get around 6 inches in length. The only other description I have is from one of the fish that was in his store at the time. It had a greyish tannish color and had a horizontal stripe running down its side that was darker almost black. When I asked him about the barbarus species he really tried to push me away from that because of the agression, but I think he just never sold any. If you have any idea of what type of mudskipper this little guy is I would appreciate it I just have not found a lot of information on the viatmanese mudskipper so I’d thought I’d see what your opinion was.
Hello Joe, Frank Indiviglio here.
Nice to hear from you again.
Unfortunately, it’s almost impossible to distinguish many of the mudskippers based on color or even photos, unless (for some) a male in breeding condition is on hand. Many are very similar, pet trade names are confusing and individuals of the same species vary in coloration at different life stages and in different parts of the range.
Periopthalmus modestus has been sold as the Vietnamese or Siamese Mudskipper in the past; however, some that I ordered under that name for a public aquarium in NYC actually turned out to be P. barbarus. The importer from whom most pet stores order usually supply Latin names on their price lists, and these are often fairly accurate…perhaps the store owner would check for you?
All species studied thus far are similar as regards territoriality, and need to be watched closely for aggression. The care of all that are commonly available in the pet trade is similar, so you’ll be safe in following the general care guidelines set out in this article.
Sorry I couldn’t offer a more specific answer; please write back if I can be of any further assistance, or if you are able to determine the Latin name.
Good luck and please keep me posted.
Best regards, Frank Indiviglio.
Hello Frank,
A relative of mine said that she was able to keep a mudskipper in a freshwater habitat. Do mudskippers require a brackish environment? I am only going to get one mudskipper, a “Vietnamese”. Would a 20 gallon aquarium be too big for it? Thanks in advance!
Hello, Frank Indiviglio here.
Thanks for your interest in our blog. Mudskippers live in habitats that vary widely in salinity…in Vietnam’s rainy season, for example, fresh water brings down the salinity until the tide comes in, at which time salinity rises again. So they are very adaptable, and can sometimes be habituated to fresh water (same holds true for other brackish water animals – fiddler crabs, puffers, archer fishes, etc.). However, they do not remain in peak condition long term in fresh water, and their lifespans are cut short. Please let me know if you need more info on vtheir care.
More space is always better…in addition to allowing for movement, a greater water volume makes it less likely that small changes in pH, ammonia levels etc. will harm the fish. Put a few small crickets in with the fish in a large tank and watch what happens!
Good luck, enjoy and please keep me posted.
Happy New Year, Frank Indiviglio.
Hello, I have recently thought about getting a mudskipper. I will probably get 2 at the most. I have a 10 gallon tank and was wondering if that would be too small for 2 small mudskippers. I would probably get 2 females. I also want to know what they can eat other than crickets. I have some gravel that is made for the bottom of fish tanks, and was wondering if that would work if I slanted it up and out of the water,or if i should get some sand on something, or a turtle dock? I have a filter, thats opening is small enough that a small mudskipper would not be able to escape, and regular lights for it. I have some fake plants and things for them to hide in, and will get some drift wood for them. This would be my first time with any type of salt water animal, how much part saltwater part freshwater does a mudskipper need?Is there anything else that they need?
Thank you so, so, so, much in advance!
Hello Mary, Frank Indiviglio here.
Thanks for your interest in our blog.
A 10 gallon would be ok for one of the smaller species, but some mudskippers reach 6” in length, in which case only 1 should be kept. Question your supplier as to the adult size when purchasing your mudskipper.
A turtle dock or other solid surface is preferable to gravel; gravel is easily swallowed along with food.
In addition to crickets, feed a variety of frozen foods – alternate between animal based foods, i.e. prawn and clam and a “complete diet” type that includes both plant and animal products.
The water’s salinity should be kept within a range of 1.005-1.015. This is determined by adding marine salt, a bit at a time, and taking readings with a hydrometer http://www.thatpetplace.com/pet/prod/209908/product.web. Evaporated water should be replaced with fresh, not salt water, as salt does not evaporate. Please check this article on Brackish Water Aquariums http://blogs.thatpetplace.com/thatfishblog/2008/02/26/brackish-water-aquarium-basics/
for more info. As this is your first marine aquarium, I suggest that you read a basic guide to marine aquariums before purchasing your mudskippers; you can check out some possibilities here http://www.thatpetplace.com/pet/cat/infoL3/22818/category.web, and your local library should have a wide selection as well.
Please let me know if you need any further information. Good luck, enjoy and please keep me posted.
Best regards, Frank Indiviglio
Hey again, Frank!
I found out what the scientific name of it is… Periophthalmodon septemradiatus. The name, “Vietnamese Mudskipper” is quite ambiguous and seems to apply to a different species. I can’t seem to find anything except for a short physical description of the fish and some pictures though. Apparently, it gets up to 10 cm long. Do you know the common name for it? Is that length accurate? If you know any places I can go for information on the care for this species, that would be extremely helpful. I don’t want to rush into it or anything.
Thanks!
JP
Hello JP, Frank Indiviglio here.
Nice to hear from you again. It’s very common for several species to be sold under a single name; this applies to many fishes, and herps as well. There are still many undescribed species that find their way into the trade, and also the same species can differ radically in appearance from population to population. Collectors are paid very little for most, and so its not worthwhile for them to take the time to weed out look-alikes. New species of turtles, fishes and lizards are often uncovered in restaurants and food markets!
The best online source of natural history info is Fish Base.Here is
http://www.fishbase.org/Summary/speciesSummary.php?ID=25083&genusname=Periophthalmodon&speciesname=septemradiatus the entry for the species you mention. As you see, there is not much available, and it is not even listed as occurring in Vietnam, and there is no accepted common English name (meaning the common name was just applied by collectors or importers, also typical).
The topics below the description contain additional information. The references section would be your best source of further details. I would check with a librarian about borrowing some of the books/articles listed (libraries can request resources from other libraries)…I know this sounds old-fashioned, but librarians are indispensible in this type of situation, and books will usually be more useful than the net.
I checked the best fish book I have in my collection on SE Asian fishes, but found no entry.
Please let me know if you need any further information. Good luck, enjoy and please keep me posted.
Best regards, Frank Indiviglio.
Hi Frank
Gert from Namibia here!
Well, when ever I want to keep an odd creature and want to look for decent info….I will always find Frank Indiviglio’s useful and professional information…LOL
I have purchased 10 African mudskippers (wild caught) and have following questions:
1: Do skippers really take up oxygen through their gills under water? Reason for the question is that my skipper aquarium has very little water and not aerated! BUT still they seem to “breath” under water…staying long periods submerged.
2: I know mud (especially when hand picked from n dam near our city) has got more than one demerit. High possibility in parasites, un-aerated clay for many bacteria …ect.
BUT as soon as I placed the skipper on the mud…I AM SHURE THEY FELT AT HOME… They darted around (not trying to get into the corners to escape anymore) and already eating and creating territories… Having them for 3 days only, I know it is hard to say but your opinion will be highly appreciated once again.
3: Last question. The skippers sometimes turn and “scratch” their heads in the mud. First I thought it to be an irritation but when I saw a youtube clip from skippers in the wild, I saw them doing the same thing in nature???
Thanxzzz once again in advance for your reply.
Best fishes
Gert from Namibia
Hi Gert,
Nice to hear from you..thanks for the kind words. Yes, the oddities always hook me..even as a child, I kept skunks in preference to dogs, native catfishes in place of guppies, etc!
As far as I know, those species which have been studied, including most that appear in the pet trade, can utilize their gills while submerged; skin assists on land. effectiveness of terrestrial vs aquatic breathing varies by species and is also affected by temperature, humidity levels etc. When given a choice between land and water, they will go back and forth and utilize the ideal breathing strategy in each; problems can occur when they are confined to either. There’s newer research, but I found this article to be quite interesting.
They can live on hard surfaces but are definitely more at home in mud, and you’ll see a variety of natural behaviors. Some of the substrates sold for use with aquatic plants work well for mudskippers…here are some examples, perhaps you can find similar locally.
Their signaling behaviors are quite complex..this could be what you are seeing; but mine have often done as you describe, and it was not related to external parasites as far as we could tell..moistening the skin may be involves?
Great that you have a large group…please keep me posted when you can, enjoy, Frank
Thanxzzz Frank! I will still look in depht in that article! In the mean time here is something else I could see: the mudskippers will most of their “resting” time lay with their mouth under water level. The gills will constantly be moving (looking as if they are drinking water) and when their heads are up, the gills will stand “open” but seen from the back…they actually are closed. This l would then take as resparation through the skin…?
What ever the case may be….one cool creature to studdy!
Their aquarium is relativly small but the smallest guy/girl seem to be less harassed…but it also seem the most cautious one…
That’s by the way the cool thing of nature…each single day something new…
Best fishes
Gert
P.S. I still need to report on the hunting method of my 3 baby sixeyed crab spiders…
Hi Gert,
Hard to say what they are doing, but your suggestion makes sense. You might wish to consider a a small submersible filter that works at low water levels; one similar to these, or this model would lessen the need for full water changes, prevent anaerobic bacteria from establishing, etc; important even if the fish do not rely on water for oxygen. best, Frank
Hello frank, I am in the process of setting up a 36x13x18 30 gallon long for 5-6 Periophthalmus novemradiatus (dwarf Indian mudskipper). It is going to be 60/40 to maybe 50/50 land to water with a wisper waterfall filter, and I’m thinking I’ll have roughly 5-10 gallons of water.
Is a top necessary to keep it humid enough for them? I live in Florida and our house stays in the mid to low 70’s year round. Also for heat I’m going to be using an under tank heating pad.
Hello Jarrod,
Interesting species…I haven’t seen them very often.
They can usually hydrate themselves well enough as long as water is available…they will enter as needed, etc. During very dry spells, a top may make it easier for them to self-regulate, but not critical. Perhaps add if you notice that they are not leaving the water. Most can jump well, so watch that they cannot get close enough to the top…climbing etc to jump out. I’ve not seen them climb glass, but check this also. Enjoy and please keep me posted, Frank