Originally Published in Herptile 29:1 (March 2004):13-20.
Further Notes on Fish-feeding in Australian Reptiles
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Fish as either a primary or alternative food source for pet reptiles have been used for some years and on many species of reptiles. Previous papers detailing the use of fish as a food for captive reptiles include Barnett (1981) and Kortlang 2001.
Both papers gave indications of basic methodology used when feeding live and sometimes dead food to reptiles. Kortlang 2001 also gave a list of Australian species known to have taken fish in the captive situation.
This paper gives a more detailed appraisal of the use of fish as an alternative food for captive reptiles, including potential pitfalls and the like (based on the experiences of myself and other reptile keepers), as well as an expanded list of species known to have taken fish in captivity.
The emphasis of this paper is towards snakes, but much has also been trialled on and applied to lizards as well.
Small, feed-sized fish make excellent reptile food, even for species that clearly never feed on fish in the wild.
While no one has yet published the results of a nutritional comparison between fish and other potential reptile foods, it's clear that most fish probably have their closest similarity to small skink lizards.
Both have similar external scales and their flesh appears to be of similar complexion.
Fish do appear to be somewhat more oily and this reflects in the scales of snakes after they've fed on fish.
However it appears that fish are digested more easily and quicker than skink and gecko equivalents of the same size.
In terms of young and growing reptiles this may mean that feeds may be more frequent, the result being an accelerated rate of digestion and growth.
By way of example, three Death Adders (Acanthophis antarcticus) fed heavily on fish in their first year attained 55 cm in total length versus an average 30 cm in the wild equivalents.
No others from the same litter (kept by other people) recorded growth rates anywhere near this.
Some species of marine and aquatic snakes are fed diets consisting all or mainly of fish and without complication.
Due to inherent difficulties in terms of getting small skinks and small rodents to feed young snakes and lizards, some enterprising keepers turned to using small fish as a readily available alternative.
Brian Barnett, Simon Kortlang, Graeme Gow, Paul Woolf, myself and others have in the past trialled fish on numerous reptile species (see list) and the fish themselves don't seem to have caused nutritional problems or led to obvious deficiencies, provided they have not been used as the exclusive dietary source (see below).
As a precaution, fish shouldn't be used as the whole or exclusive diet for most land-dwelling snakes (or lizards) kept. But they remain a readily obtainable standby that can be stored in the freezer in the event that other foods are hard to obtain.
Reported on a number of internet lists has been that snakes fed exclusively on fish have been found to have seizures and in some cases death within as short a period as six months.
This is believed to be due to a thiamine (Vitamin B1) deficiency (also see Barnard 1996 and Mattison 1982).
To counteract this risk, fish shouldn't be used as the sole diet for snakes, even though they appear to be an excellent food choice.
If they are to be used exclusively (not recommended), then the diet should be supplemented with a vitamin and mineral powder, or piece of a Brewer's Yeast tablet that's placed inside a dead fish's body before it's fed off.
Another alternative is to use a scrape of 'Vegemite' on the food as this is high in thiamine and will help avert later deficiency.
Vegemite has been used as an additive without incident for snakes fed on fish by myself without any problem. Notable is that snakes fed fish and given this additive have never presented with thiamine deficiency.
If a snake presents with nervous behavior and seizures believed to have resulted from an all-fish diet (thiamine deficiency), a small amount of B-complex vitamins should be administered intramuscularly. The symptoms usually subside within hours.
FISH FEEDING: THE DETAIL
When testing fish on reptiles, the fish of choice for Kortlang and Barnett was goldfish which when dropped into a cage would flap about and be seized by the (usually adult) reptile. The reptile would then eat the fish.
Some snakes that ate live fish failed to kill them first and later suffered internal injuries and sometimes death as a result.
This was usually seen by the snake or lizard jerking uncontrollably as the fin spines penetrated the snake's digestive tract.
Use of dead fish effectively removed this problem.
Dead fish aren't always accepted by snakes, but when force-fed, seem to be digested without incident.
Some snakes (juvenile and adult) have shown (in the first instance) a strong dislike for eating dead fish, but would digest them when force-fed them and so were trialled again on fish several times, whereupon they appeared to get used to them and inevitably start taking them of their own accord when presented with them.
The sharp-edged bones of fish are notorious and perhaps best seen in photos of snakes feeding on fish.
Not only that, but the pasty flesh of fish makes the bones protrude, often even before the fish are swallowed.
Because of this, one should be particularly careful when feeding any fish to reptiles (in terms of size and bone structure).
Most snakes offered fish seemed to find the scent of fish favorable and would readily take a dead fish held in front of them on forceps/tongs, although many neonate snakes were force-fed in the first instance before taking fish on their own accord on later feedings (see later).
Fish swallowed backwards don't tend to swallow easily due to their spines facing into the snake's digestive tract as they move down (in much the same way as a rodent's limbs do when swallowed backwards). Thus some snakes that tried to eat fish tail-first ended up giving up and regurgitating half-eaten or half-swallowed fish.
Noting this same potential hazard in the event of regurgitation, it's also recommended that larger sized fish (relative to the snake) not be fed.
In other words:
Stick to these rules and you shouldn't have problems.
The size of fish fed to the snake (usually) is determined by the size of the reptile. Wild-caught fish are excellent for some snakes, especially if the fish can be easily caught in large numbers.
Freshwater fish have mainly been used and so the effects of marine fish species being fed on non-marine reptiles isn't well-known (at least for Australian species).
However trials with saltwater fish such as Flat-tailed Mullet (Liza argentea) and Whiting (Neoodax balteatus) were favorable.
Both were readily taken by an adult Carpet Python (Morelia macdowelli) who followed onto the fish when first fed a rat.
The fish eaten were the sizes of large rats and are believed to be the first Australian trials of rat-sized fish on terrestrial snakes.
Other than a visibly more oily skin, the snake's health appeared perfect and it's condition appeared to have improved more from the fish than it would have from equivalent sized rodents.
Death Adders (Acanthophis antarcticus and Acanthophis cummingi) have been fed mouse-sized Sardines (Sardinops neopilchardus) with similar positive results.
Younger snakes of several species have also been raised on Whitebait (Galaxias sp.) without incident.
The introduced American Mosquito fish (Gambusia holbrooki) and various introduced guppies (including Poecilia reticulata), common to ponds and lakes in all Australian cities is an excellent alternative food source for small pythons, elapids and skink-feeding species due to the huge numbers that can be caught with a small flymesh style butterfly/tadpole net.
They are also excellent for the purposes of raising large numbers of young snakes.
The numbers of these fish tend to peak in the late summer. A couple of hours by a decent pond can yield hundreds of adult-sized fish, with each being roughly equivalent to a newborn mouse. These can usually supply a reasonable number of small snakes for another year.
The fish are stored in small lots in a freezer inside unused plastic coin bags (which can be got free from most banks) and thawed out as needed.
In some parts of Australia there are seasonal surges in native species such as eels and Galaxias (Galaxias spp.) which also make excellent and inexpensive food for smaller snakes.
If using native species, you should check to check first to see that your local laws allow it.
Put another way, catching or buying small fish is a lot easier than trying to find lots of 'feed skinks', or otherwise obtain equivalent sized small mice.
In the past young eels (elvers) were sold commercially from Tasmania to snake keepers in mainland Australia. However the supply has been patchy, in part due to the ever-changing legislative regime in Tasmania.
The best equivalent available is Whitebait (Galaxias sp.), which are available frozen all year or fresh at certain times.
Easter is usually about when fresh whitebait are sold at retail outlets and they can be had for about $3.50 per kilo or 3.5 cents a fish.
At that price, it's doubtful if any other reptile food can compare in terms of price and value.
For this and all other species of saltwater fish fed to snakes, a side-effect of their use as food is that the snake that eats them may drink slightly more than would otherwise occur after a feed.
Assuming water is always present in the reptile's cage, then this shouldn't be a problem for the keeper.
Fishing nets in the form of 'bait traps' are also excellent for catching large numbers of most kinds of fish except for surface dwelling types like Gambusia.
A pair of traps, bait and cod-liver-oil for the bait can be had for about $30 and if placed in a decent watercourse such as the edge of a lake can yield hundreds of small to medium sized fish within a couple of hours.
Among the better sites are drainage ponds for power plants, such as the Hazelwood power station cooling ponds in the Latrobe Valley of Victoria.
These ponds are typically filled with water from cooling towers and are generally warm enough to support large numbers of introduced tropical species at all times of the year.
A final word of advice regarding traps and nets is as follows.
Sometimes they are sold as white material, which is as made. However fish readily see white nets in water and will avoid them. The net must be greenish or muddy green in colour for best results.
If the net or trap netting isn't that colour already, your should buy some dye and make it that way.
FORCE-FEEDING FISH TO YOUNG OR RELUCTANT SNAKES
Force-feeding of reptiles, is a tricky topic among keepers in that many express wildly differing views.
In my view, force-feeding of reptiles, if done properly (which means quickly and as painlessly as possible on the reptile) should have no serious or detrimental long-term effects on the reptile.
In terms of young reptiles (mainly snakes) that may otherwise not feed, force-feeding may be a useful way to get the reptile into a feeding and growth routine quickly, after which the reptile can be more easily induced to take food on it's own accord.
In terms of my own raising numbers of young Death Adders (Acanthophis) and Pythons (various species), most are force-fed for their first few feeds (at least) immediately following the first slough (or if in a large group, when most have sloughed, all are fed at the same time, even if some haven't sloughed).
This is often done without offering them the chance to take food of their own accord as it's presumed they won't voluntarily take a dead fish on their own in the first instance. It's also generally done on all snakes at once in a 'conveyor belt' arrangement of one after another.
For ease and convenience the same time feeding routine is continued for some months and may include snakes with cloudy eyes, which can still be force-fed without problem.
Because fish of almost any size are readily obtainable, fish of the desired size can always be obtained and force-fed to given snakes, either by capture or from a fish market.
Obviously fish with large and protruding spines (common to many species) are avoided.
Their cylindrical shape of fish also makes for easy force-feeding.
The only problem with fish is that their pasty flesh may make them come apart before they are pushed down the snake's throat. This is particularly if using fish that have come out of a freezer and been thawed out in warm water.
In terms of the force-feeding, the fish is best forced down the snake's mouth and throat using a pair of forceps.
If the fish is held by the spine or (later) the tail, disintegration of the fish's underbelly is usually avoided.
In the event that there is some disintegration and fluids escape into the snake's mouth and nearby areas, the snake will usually be content to continue feeding.
When force-feeding the snake, the method of choice (which also avoids bites) is as follows:
The snake is placed on a flat surface (which may be in the cage). The head and neck is pinned flat, and then held down with a hand. Using the other hand forceps are used to force the fish into the snake's mouth and down the throat. Forceps are easier to use than hands, even for harmless snakes for which there is no hazard from inadvertent bite. In order to make the force-feeding action easier, the snake's head and neck region should be held in a straight line and rigid, so as to prevent any obstruction that may otherwise occur if the snake is to twist it's body. In line with this recommendation, it's also best to hold down and flat the rest of the snake. The fish is usually pushed down the throat so that only the end of the tail is left in the snake's mouth. Then, either on the flat surface or back in a cage, the snake is allowed to continue to eat the food or resume it's own feeding action. Sometimes making the snake move forward will speed this up, as this is part of the natural feeding response for most reptiles.
In terms of young snakes, the feeding response will usually take place so long as the fish is pushed more than halfway down the throat.
As young snakes get used to the process they will as a matter of course resume the feeding response more and more quickly once the fish is placed in the snake's mouth.
Before long, all snakes will learn to eat fish when offered to them if they are hungry.
However by using a more proactive force-feeding regimen for young snakes, especially with fish, growth can be maximized and young snakes can be raised to a larger more hardy size faster.
The important thing to note is that a snake that is force-fed (even if it would normally eat on it's own), will not have it's self-feeding habit affected in the event of it being force-fed for a period of time by a keeper.
The only contraindication is that caused by regurgitation.
If this occurs and the reason is overfeeding, then obviously food intake should be reduced.
Finally, it's also worth noting the wet and sticky nature of fish flesh, including any that may be hanging out of a snake's mouth.
This will attract any loose dirt and other substrate that will invariably stick to the fish. This effect may irritate the feeding snake sufficiently to make it want to stop eating and throw-up the half-eaten fish.
This latter possibility is effectively avoided with due care by feeding in a situation where there is little if any loose substrate.
Numerous reptile keepers have provided input for this paper.
With specific references to the use of fish as reptile food, are the following:
Brian Barnett, Scott Eipper, Adam Elliott, Simon Kortlang, Andrew Lowry, Paul Woolf.
Barnard, S. 1996. Reptile Keeper's Handbook. Krieger Publishing, Malabar, Florida, USA: 252 pp.
Barnett, B. F. 1981. Observations of fish feeding in Reptiles. Herpetofauna 13(1):11-13.
Kortlang, S. 2001. An alternative food for reptiles - Fish. Monitor - Journal of the Victorian Herpetological Society 11(3):14-16.
Mattison, C. 1982. The Care of Reptiles and Amphibians in Captivity. Sterling Publishing Company, New York, USA: 184 pp.
Australian Reptile Species That have been successfully raised or kept on diets incorporating whole fish.
Note that the bias is towards those species most commonly held in captivity. Other less commonly kept reptiles can no doubt also be kept on a diet that incorporates fish.
All fresh and saltwater Chelids
Various (presumably all) species of family Hydrophiidae
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