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Introduction to the Freshwater and Brackish Water Puffers.
By: Robert T. Ricketts


Puffers are a fairly small group of fish. Dr. Klaus Ebert suggests there may be something like 150 species (Fishbase lists 121). But the taxonomy is highly uncertain. They are largely tropical. There are a few temperate, with no cold-water species known to date, and they are worldwide in distribution but with the majority in the southern hemisphere. Fewer than 40 species are considered freshwater (FW) or brackish water (BW). Obviously most puffers are marine (SW), but a number of those are sometimes found in brackish or even fresh water as juveniles or spawning adults. A number of marine forms, not just puffers, do return to estuaries or mangrove swamps to breed. The fry and juveniles are common there as these are highly rich environments for fry as well as adults. Puffer size ranges from about an inch (total length) at maturity (the perhaps two, or perhaps three, "new" species of FW dwarf puffers) to just over two feet in FW, almost to four feet for SW. Standard length, by the way, is the measure from nose to caudal peduncle, not including the caudal (tail) fin itself. Total length would be the measure including the caudal fin.

Fahaka, Nile puffer
Tetraodon lineatus the Fahaka, Nile puffer.

All known puffers are largely predatory, some preying on snails, shellfish, and crustaceans by active hunting, others are lurking predators of other fish (piscivores) or wandering crustaceans and mollusks. SW puffers may consume more vegetable matter than FW and BW puffers. The FW and BW puffers tend to eat green food mainly by chance, when they bite a snail with a bit of the plant on which it is grazing - a small side salad, as it were. In captivity most puffers can be trained to (thawed) frozen foods along with live. But it must not be forgotten that their dentation is key to their diet. They are adapted principally to a high protein diet packaged in a hard shell.


Their strongest single obvious family characteristic is the fusion of their teeth into four bony plates, two upper and two lower, matched with strong jaws such that they are well equipped to crush the hard shells or bones of their prey. Those fused teeth, dental plates, are the character for which they are named, the Tetraodontidae family - meaning "four-toothed" in reference to the four fused plates serving them as incisors. They also have pharyngeal teeth for additional grinding of crunchy foods. They do also share the major anatomic adaptations required to be able to inflate their bodies with water, including loss of the paired pelvic fins, loss of the ribs, being scaleless, and having uniquely specialized skin and stomach. It might be worth noting that the puffers and their near kin as a family lack other close relatives. Anatomically and phylogenetically they are in a relatively isolated family. Their adaptations are extreme, but highly successful.

Among their feeding and defensive specializations, they have lost their pelvic fins. Normal swimming is largely by the transparent pectoral fins, with extra guidance and a bit of drive by their symmetrically positioned dorsal and anal fins. The caudal fin serves generally as a rudder, but the body-and-caudal fin swimming used by most fish for propulsion can be employed for bursts of speed from most, and likely all, of this family. Their bodies tend to be chunky, some almost blimp-like (near tubular), some being a bit flattened side-to side, and others flattened top-to-bottom. The gill openings are not hard opercula as on more familiar fish, but smaller, softer skin openings near the pectoral fins. Many puffers show iridescence on their eyes (corneas), commonly a very nice blue - I believe this to be a light-control (or perhaps glare-control) measure for them in the wild. Their eyes are so positioned and muscled such that they can use binocular vision for depth perception quite well and do so in their browsing for prey. They appear different from most tank fish in part due to the modifications required for puffing up, including no ribs, which also impacts their variant swimming techniques.

Puffers are scaleless, most with spines that are not always apparent. They have the ability to inflate their bodies with water in their stomach when threatened, which makes them appear much larger and which also erects their spines. They have special stomach valving which allow them to swallow and hold water to expand their stomach and body to several times its normal mass. Their stomach and skin are elaborately pleated and folded normally or highly elastic to allow this expansion. This mass change in configuration, plus the spines which erect as the skin is stretched, should make them appear far less appetizing to potential predators. If that should fail, they might get their revenge after the fact, as they are or may be toxic. Their primary toxin, tetrodotoxin, is one of the most potent biological neurotoxins known. The notorious Australian blue-ringed octopus uses the same toxin, along with a variety of other critter from newts and frogs through worms and shellfish. The Japanese eat SW puffers (fugu) as a specialty, as the toxin is most concentrated in certain tissues and consuming the muscles results only in mild tingling and numbness of the fingers, toes, and lips - unless the specially licensed chef made a slip, in which case you die without intensive medical care. In FW puffers the toxin may be somewhat modified and differently distributed (lots in the skin). The common freshwater puffer toxin is the closely related Saxitoxin. The toxin is not manufactured by the puffers, but eaten from the environment. The toxin is bacterial in origin. Captive puffers do tend to lose their toxin over time, just as the captive poison dart frogs do, as the producers of the material are (hopefully) not present in the captive food chain. The toxin is not released into the aquarium water by the fish. Freshwater puffers tend to high concentrations in their skin, so direct handling is not a good idea with newly captured specimens, but then, no fish should be directly handled other than for special procedures.

Many of the active hunters in the FW and BW groups characteristically squirt water jets from their mouth at the substrate (an alternate idea for the origin of the name "blowfish"?). This helps uncover potential prey bivalves, crustaceans, or other mollusks, or worms. In captivity it is not rare for them to squirt water from the aquarium surface at their owner - a not so subtle feeding hint? Their aim in air is not as good as archerfish.

Puffers, like many Cichlids, tend to be very long-lived fish. With proper care most should live beyond ten years, many to the mid- and upper teens. I suspect that like, but still less than clown loaches, they could make it into the twenties with excellent care, and I just haven't managed them that well - yet.

These fish are as group intelligent, high personality fish. They suffer from being "cute" and all but irresistible, or they are irresistibly weird almost to the point of being alien. Given the unavoidable confusion and/or lack of information on the nature of their native water and even the correct identification of the fish and of their needs, this frequently leads to premature death of the fish and often of their tankmates. There are several topics that need to be considered in the care of these critters: aggression, intelligence, feeding style, water nature, and water quality.

Aggression & Intelligence: These fish are in general not trustworthy with tankmates. There are reports on the boards after I've made such comments from folk who report no problems with puffers even in typical community tanks. So I tend to ask the length of time this setup has been stable. If I get an answer at all it most often ranges from a couple of weeks to a number of months. Long term mixed tanks are rare. These fish are very Cichlid-like in many ways. They are intelligent and adaptable. They are also very long-lived and not fast to mature in captivity, especially without proper diet and water conditions. When they do mature, just as with many Cichlids, the world changes. Some individuals of many common (in the trade) species will be relatively good guys. Others will be dog-in-the-manger and only occasionally cause damage. Still others make Jack the Ripper look like a Sunday School teacher. And that is within a single species. Some species tend to average a bit milder than their kin (Tetraodon biocellatus - the Figure-8 in brackish water, and Colomesus asellus, the South American FW puffer, in freshwater). Such puffers can be kept (given sufficient room) with conspecifics (others of their own kind). But any given individual puffer can behave anywhere on the scale. Tetraodon lineatus is at the bad-guy extreme - they cannot be trusted with anything, anytime post puberty. Plus any puffer, if hungry, may decide that even a long-term (years) tankmate looks like lunch. Size of the target is immaterial. Their dentation is such that they can bite through bones and most armored scales.

The lurking piscivores (fish eaters) tend as a group to be a bit more forgiving of conspecifics or even other tankmates, provided they have their own security spot. These are also among the least active of hobby fish. They seem to move mainly in the search for or in the presence of food, or in warning off others from their boundaries of their "secure" area. But then again, they may consider tank mates food, whether eaten whole or just having a bite removed, which of course may be fatal to the victim. Some of this lurking subgroup will benefit from the finest textured substrate practical, as they may prefer to bury themselves at least partially, with their eyes out (a bit like flounders) to watch for passing prey. Some puffers from the hunter group, especially when young, may also show this concealment in the substrate also.

Puffer bites on conspecifics are frequently territoriality and/or food access disputes. Such bites show up well on the bitten fish a neatly round bite marks that are surprisingly non-serious. They tend to heal quickly and cleanly. If there is insufficient space in the tank and/or insufficient refuges and visual complexity (out of sight is out of mind), the fights may escalate to permanent damage or death. But the commonest puffer-to-conspecifics puffer bites are warnings, not attempts to eat. As an aside, puffers are immune to puffer toxins.

For the active swimmers, in my experience, water volume and setup visual complexity are also great aids to peaceful co-existence. Judging tank size requirement by the adult size of these fish is woefully inadequate. Give them lots of swimming space and a complex environment and you have a better chance of success. Also provide refuges, more than the number of specimens housed - i.e., if you have three puffers, provide at least 4-5 or more caves, overhangs, bogwood tangles, plant thickets, whatever. This gives them choices of security spots for sleeping or resting. The visual complexity bit means not having clear sight lines throughout the tank from the fish's viewpoint, not the tank observer's viewpoint. This is a key difference. Blocking their sight lines need not block your own. You are looking from the outside in. They are inside and looking primarily within the tank (but are certainly highly aware of movement outside it as well). Carefully placed real or artificial plants, rockwork, etc. can help provide visual barriers for the inhabitants without seriously blocking your own view.

Some active hunters develop stereotyped swimming in tanks. They adopt one area of the tank wall and swim up and down there repeatedly, chronically. This is most often seen in an area of detectable current, as where flow from a filter hits the tank wall. To me this is identical to the pacing of caged zoo animals that are inadequately housed and exercised. If the environment is larger and more complex, and with good current, you may see less or none of this. If this behavior appears it is not terrible, just not desirable. Animals in the wild have certain lifestyles, and if they are roaming hunters, they "need", are hard-wired, to work off some energy - even if just by swimming up and down the tank glass for a puffer or pacing the cage for a captive big cat. It is as close as they can come to a treadmill. If this behavior occurs in your tank, you can control the location where it is done in part by current. Rearranging your filter outlet flows can cause relocation of the selected site. But to get rid of it altogether before it becomes a fixed habit (stereotyped) requires moving the fish to a much larger and more visually complex setup with more current, at least in my experience.

Most puffers can become nippers of the fins of other fish in their tanks, whether conspecific or unrelated. Depending on many factors, the nipping or biting causes stress at least, up to the directly or secondarily injury-related death of the injured fish. Unlike the case with many other predatory fish, relative sizes between the puffer and its target are trivial. A puffer has little or no hesitation to "taste" a fish many times its own size and mass. Once a particular fish has started nipping or biting or killing tankmates in my tanks, that behavior seems quickly to become fixed indefinitely. After that they are suitable only for solitary tanks. There are very wide individual differences within a species of puffers, just as there are broad differences between species. No one can predict what any given puffer will do or exactly how it will behave at maturity. If you hear claims to the contrary, take them with a large grain of salt.

Feeding style: The lurking predators can be trained to thawed frozen and pre-moistened freeze-dried (FD) food with a little patience, but you are likely to have to start with some type of live feeder. If possible these should be disease free and well fed or at least gut-loaded (you are what your prey eats) and would be best if not fish. Many will accept brine shrimp when the fish is very small (as will the smallest of the active hunters), live ghost shrimp when larger. Both of these are far safer than LFS "feeder fish". Frozen silversides thawed and threaded (no knot on the end of the thread please - we are not fishing here, we're training to non-live food) onto a piece of cotton thread can be dangled in front of the lurker to simulate a live fish. Pre-soaked larger FD krill can be handled the same way. Either food may be skewered on the end of a bamboo skewer as well for offering to the fish, or held by large forceps. Eventually even thawed frozen clam or squid (smelly but a favorite) will be accepted. I am a firm believer in variety in a captive animal's diet. We have little data on the long-term value of particular foods, and less data on the long-term needs of long-lived fish such as puffers. A variety of foods is much safer, one food compensating for another's lacks or excesses. Certain species do require very high "crunch" in their diet to keep their incisors worn down, so are best fed with as many snails as practical. The lurkers as a group are less demanding on the crunch factor than are the hunter-predators. Many puffer keepers use vitamins in the water in which they pre-soak FD foods or thaw frozen.

The active hunters tend to more invertebrate diets than the lurkers do in nature, seeking snails, crustaceans, and exposed bivalve mollusks. Most will not turn down an available fish however. All of my pets in this group are fed snails regularly (I raise these for feeding see the article: Breeding Snails for Food ) Hard shells are required to wear down the bony plates these fish use to bite and crush such prey. Like rabbits, their teeth grow constantly and can overgrow enough to cause starvation in the fish. Small bivalve mollusks or frozen cocktail shrimp or larger krill with shells will help this, but for me snails are the best (and I know they are safe, I raise them through many generations and feed them a varied diet). These are offered to the lurkers as well, but not all lurkers are interested in snails. These fish will also adapt to frozen clam and squid. Clean earthworms seem to be relished by most puffers, but as with other unfamiliar foods, it may take a few tries for them to realize that this new item in the tank is food. Foods as soft as earthworms should not be staples for any captive puffer larger than the dwarf Puffer- live blackworms are big to them, but are a staple for me with them. The dwarf puffers are unique in seeming to have no dental wear issues.

Garlic does seem to be an appetite stimulant for puffers as it is with a number of other captive fish. If you thaw and rinse frozen foods, a bit of garlic juice or extract dropped on the food or in the cool thawing water may speed acceptance.

Just do not expect your puffer to live long and do well on prepared flake or pellet food, it just ain't gonna happen.

Puffer's bodies are not as unchanging as more familiar fish (a side effect of the ability to puff up and the lack of the ribs that requires) and potbellies are easily noticed after feeding. Other than the smallest and youngest specimens, daily feeding is not required and may not be desirable. As the young but still immature fish grows, feed three day and skip one. Then feed two days and skip one. Finally feed every other day. Every other day is fine for the more than half-grown or larger active hunters, less often for the lurkers (at maturity mine are fed every third to fifth day). As these fish are again like some Cichlids in being messy eaters, this will help control the excess bioload demand on the tank as well. If you feel that you must of should feed still-immature fish daily, reduce the portion size accordingly. I still would suggest skipping at least on day per week without feeding for any fish past fry stages. The old saying about a lean horse for a long race applies quite well to captive fish. Overfeeding is just as harmful to puffers (and other fish) as it is to humans.

Water nature: This is a hard one. Puffers in local fish stores (LFS) are mislabeled more often than not. Salespeople in those same LFS are generally even less informed about this group of fish than almost any other. They may assure you these will be at home in a normal small to medium community tank (but they may say the same about those cute baby Oscars), and will eat flake foods and prosper. If you are considering a puffer purchase, even more than most fish, you absolutely must research the particular fish before you buy.

The best text reference, also by a very wide margin is the Aqualog hard cover by Dr. Klaus Ebert, The puffers of fresh and brackish waters. This is not an inexpensive book, but for photo identification and for care and handling tips, it is irreplaceable.

If some website says that a certain fish is FW, you will likely find another saying it is brackish and a third saying marine. Pick your experts with care. I won't say bad things about the several hobby sites as there is a lot of useful info on these, but they are not all well researched or authoritative and many do have glaring errors that may sit uncomfortably side by side with excellent advice. The novice cannot be expected to tell the difference between the wheat and the chaff on such sites.

Fresh water puffers are just that, fresh water fish throughout their lives. Being secondary FW fish, they tend to be quite adaptable to water conditions, as actually are most of the fish in the family. But pushing a FW puffer into middle density brackish water is not going to be the best thing for it, marine conditions would be even worse if it survives at all. My tap water is moderately hard and somewhat alkaline and the FW puffers do fine for me in that water. Many FW puffers are riverine fish from the tropics. As such they are adapted to varying water conditions through the course of the year, from softer and more acid but muddy or silted during flood or rainy season, to the higher mineral content but less silt during the dry season. They are by this more adaptable, within reasonable limits.

Brackish water puffers are harder to pin down. Many of these are sold as FW in the LFS, but trying to keep them there is not beneficial. In such water they will be subject to many diseases (Ich and fungus are nightmares in this situation), show poor color, and are likely to be quite stunted in growth. To me one mark of an uninformed site is one that states that the puffers (or any other fish for that matter) will be smaller in captivity than in the wild - a sure sign that their knowledge or information or their tank-keeping practices are not sufficient for proper care. Well-kept captives should meet or exceed wild size and generally should greatly exceed wild lifespans. If they do not, it means that we do not know enough of their needs, or do not practice what is known. Even if purchased from FW, I start moving these fish to light brackish (specific gravity 1.003 -1.008) gradually over days to weeks while they are in quarantine (QT). Aragonite (or crushed coral, but aragonite is more soluble) substrates or filter loads are used to help maintain a stable alkaline pH. Only marine mix should be used to prepare the brackish water, and this needs to be done at least a couple to several days before use to allow mixing and solution of all the components. The elevated pH and the complex mixture of salts in the mix are important (IME) for these fish, not just sodium chloride (NaCl, plain salt). Whether you hold the fish at that level or move them to mid-range brackish (specific gravity 1.009 - 1.015 for my usage) is pretty much personal choice in my opinion. Many folk who are long-term successful with puffers do so (some even to full marine conditions, specific gravity 1.020 - 1.025), but I tend to hold light brackish for most of these fish. Some BW puffers should move to marine or near-marine conditions as adults, and perhaps surprisingly, this is easier upkeep for the hobbyist. Obviously buckets, spare tanks, or Rubbermaid food-safe containers are needed for water mixing, and these are best fitted with a sponge prefiltered powerhead (to protect the impeller from un-dissolved salts) and a heater as required. A full range specific gravity measure will be needed also - for me the standard floating arm plastic box style hydrometer such as the Aquarium Systems unit is quite accurate enough. Any hydrometer is best calibrated against a refactometer, but this is not an absolute requirement. Stability is more important than an exact measure for most vertebrates. Brackish water puffers are as a group not terribly sensitive to small fluctuation in specific gravity. It is the nature of the waters that they inhabit in the wild and they are well adapted to that.

All puffers need QT even more than other fish. They tend to be transported seriously overcrowded for such feisty fish (resulting in nips and bites, and possibly ammonia stress as well), subjected to multiple water changes of variable hardness and alkalinity, and to have both Ich and fungus from all this (I hope unintentional) abuse. As almost all puffers are wild caught, assorted intestinal and somatic parasites are a real possibility. They also tend to be starved. As is the case with Otocinclus catfish, not all these fish are able to recover. Look for the best possible color and some evidence of having been fed and having eaten. Hollow and/or dark bellies are not a promising sign. Leave such fish in the store unless you are quite experienced. Expect to use heat and salt (or marine mix in this case for BW fish) to clear their external problems while in QT. This period also gives you the opportunity to learn the feeding habits of your new fish and start working on a sustainable diet for them.

Water quality: Puffers are basically hardy once adapted to you, your tanks, and your care. They are easily and seriously stressed by the un-oxidized metabolites in uncycled tanks, so do not need that stress in their lives. As noted above, they are very messy eaters and copious waste-producers. If the earlier advice on over-sizing their tanks is followed, this will help. So will controlling the quantity of their food. Like goldfish and Oscars, they are master beggars and will not stop eating until apparently nearly unable to swim, if allowed. Expect to do plenty of water changes at substantial percentages of tank volume, even though by community tank standards the tank may appear to be lightly to very lightly stocked. My personal feeling is that their response to less than good water quality is stunting of the fish. Many hobbyists report several years old puffers still at near LFS ordinary sale sizes. As I do not often see this myself, I suspect it is a complete care issue, but with tank size and water quality playing major roles here. Quite similar situations are seen with too many hobby goldfish, Oscars, Clown Loaches, and entirely too many other commonly seen pet fish. As with those other fish mentioned, puffers cannot successfully be moved up in tank sizes "as they need it". If the keeper thinks that they need a larger tank, it is almost certainly too late already. If you cannot start post-QT with the generous permanent home suitable for the fish for the rest of its life, perhaps you should consider smaller and less demanding fish. Big fish, especially big predators, are quite different in nature and needs from small pretty schooling fish. Fish grow most and fastest as juveniles. They never really stop growing, but post-puberty, the growth rate slows markedly. If they do not make a significant percentage of mature size before they are sexually mature, they likely never will.

Appearance and color: By the way, puffer appearance and coloration is not as fixed or stable as many of our familiar fish either. Most puffers have "sleep" coloration that is much paler and less sharp than their daytime markings. The same or similar coloration may show when the fish is stressed or unwell. Dark bellies are a sign of stress in white or light-bellied puffers. Seeing this infrequently is not cause for alarm. Seeing it routinely or regularly means attention should be given. Puffers commonly fold their caudal fins alongside their bodies while sleeping. This can also be a submission signal from wide-awake fish in multi-puffer tanks. Many hunter-predators fold their caudal fin forward against their body while resting and/or sleeping. They may also do this while examining potential food items, as the caudal serves as a rudder and would otherwise hinder "helicoptering" around the item of interest. "Helicoptering" is the term used for a hunter-predator puffer examining a potential food item closely and at some length - mouth toward the potential prey, both eyes focused on the prey (binocular vision, remember?), body perpendicular to the prey, with their pectorals and anal and dorsal fins sculling, they can rotate around the prey as if on a string anchored at the prey. Nothing much beyond a dwarf puffer can do that in a small tank, and very few fish are physically capable of such motion in any case. These are strange and wonderful pet fish.

Robert T. Ricketts, a.k.a. RTR




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