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You are here: Home Volume VI December 2007 Feature Article: Chronic Anorexia in Aquarium Fishes

Feature Article: Chronic Anorexia in Aquarium Fishes

By Jay Hemdal Posted Dec 14, 2007 07:00 PM Pomacanthus Publications, Inc.
Don't fall into the trap of assuming the fish will begin feeding when it gets hungry enough, or conclude it must be eating something, just not when you are watching.

Fish that refuse to feed in captivity is a problem for most aquarists from time to time. Once this difficulty begins with a particular specimen, the clock begins ticking; if the issue is not resolved within an appropriate period, the fish will die. Acute anorexia (where a fish suddenly stops feeding, or never starts feeding, and soon dies) is usually caused by some environmental issue; water quality problems, disease, transport stress or tankmate aggression. Chronic anorexia is a rarer problem, where the fish has apparently adapted well to captivity in all respects except that it does not show a normal feeding response. The term anorexia is replaced with inanition (loss of energy due to lack of food) or inappetance (lack of appetite) by some authors. In the cases described here, the term anorexia is perhaps a better fit as it is defined as "an aversion to food due to serious psychological problems". In some cases, the fish had been feeding well and then stopped for some unknown cause, in other cases, a newly acquired fish refuses to feed despite its apparent environmental needs being met. Weight loss may or may not be apparent in the animal, and inanition is not observed until just before the fish succumbs to the long-term problem. As the following case histories show, some fish have gone without food for extended periods and subsequently recovered. These are mostly older, larger fish, or those kept in temperate (cool) waters. At the other extreme, a post-larval butterflyfish may succumb if it goes even a few days without food.

There is a preferred course of action one should take to try to get a chronically anorexic fish to begin feeding. After the environmental problems mentioned above have all been ruled out, the second, most obvious step in resolving this sort of problem is to make certain that the food being offered is of a type and size known to be accepted by other members of the same species of fish. If the captive diet of the fish is unknown, or if the species is known to be a difficult feeder, the problem may not be just with the one specimen, but rather with the entire species. Assuming that other specimens of the same species are known to feed well on the food being offered, the next step is to change the delivery method. For predatory fish, stick feeding will sometimes work to get the fish feeding normally. Simply put, a food item is impaled on the end of a long stick and offered to the fish. However, there is an art to this delivery method. First, different species react in diverse ways to the presence of the feeding stick. Some fish ignore the stick, while others seem to shy away from even the thinnest, least visible of sticks. When in doubt, opt for a clear or very thin feeding stick. It seems that the end of the stick closest to the animal causes the most problem. Using a short length of heavy monofilament fishing line at the end of the stick helps make it less visible to the fish. Avoid wire or other overly stiff material as the fish may strike at the food, but then back away when it touches that material.

The tube-feeding process can be employed to give a fish food energy during the time it is anorexic. In some cases, this gives the aquarist enough time to determine a permanent solution. This process uses simple equipment - a syringe and a flexible plastic tube. Feline urinary catheters or avian tracheal tubes can be used for small fishes (Hemdal 2001). Larger fishes can be fed using standard airline tubing attached to a large syringe. A Luer-lock syringe will hold the feeding tube more securely to the syringe body. It helps with placing the tube if you first bevel the end of the tube. The tube should have marks on it at regular intervals so that you can more easily judge the depth of insertion.

The basic food recipe is to create a liquid that will easily pass through the feeding syringe and tube, but thick enough to carry a high amount of calories to the animal's digestive track with the least amount of water. It is best to prepare this slurry in a blender, using materials that would be components of the fish's normal diet.

The amount of food administered at one feeding is generally 2 to 4% of the animal's body weight, just enough food to cause a slight distension of the animal's belly. (Hemdal 2006). In most cases, the use of an anesthetic such as MS-222 is required to sedate the fish so the tube can be inserted. Holding the fish on its back, gently insert the tube into its mouth and try to locate the esophagus. If you are too far one side or the other, the tube will miss and emerge from under one of the gill covers. Once in place, gentle pressure on the syringe plunger will move the liquid food into the fish's stomach. Once fed, the tube is gently withdrawn and the fish is moved to a recovery tank (Hemdal 2006). Spontaneous regurgitation is the most commonly seen problem, although there are reports of people accidentally rupturing the fish's digestive track. Like any medical procedure, there are subtle techniques for this process that need to be learned through practice - so please do not expect to read this basic introduction and suddenly be proficient at tube-feeding fish.

some_adult_scorpionfish_resist_feeding_on_prepared_foods_when_first_collected.jpg

Some adult scorpionfish resist feeding on prepared foods when first collected.

Force-feeding is a technique that can be employed on larger carnivorous fishes. A sedated fish is held on its back while its mouth is opened. A food item of appropriate size for the animal is then placed in the back of the animal's throat. A finger or semi-rigid tube is then used to gently push the food item into the stomach. In some species such as anglerfish and eels, there are back-curved vomerine teeth in their throat that will actually grasp the food item and keep the fish from voluntarily regurgitating it.

Be cautious in directly handling a fish during either of these two techniques as some have very sharp teeth, and of course, some fish have venomous spines.

Case histories

The following are a series of case histories of long-term anorexia syndrome in aquarium fishes. All of this data was collected from the experiences of various aquarists from around the world (Including some from the author). Please understand that these observations are all subjective, and there may be details lacking that might hinder their application to resolving other cases.

That said, limited (but potentially important) conclusions can be drawn from these case histories. First, in larger fishes, long-term anorexia without concurrent loss of body condition is very often a reversible health issue. Tankmates of the same or similar species sometimes help "train" anorexic fish to feed properly in captivity. While this behavior modeling does not always work, if there are no other compelling reasons a newly collected fish is not feeding, it often turns the tide for a non-feeding fish. When done properly, assisted feeding (force-feeding or tube-feeding) can either "jump-start" an anorexic fish's metabolism, or at least help it maintain body mass until the fish begins feeding on its own. Perseverance and patience are important traits for an aquarist; as long as the fish is not overtly suffering, waiting a bit longer, or trying a different method to offer it food may eventually succeed.

Japanese roughy, Gephyroberyx japonicus

Three deep-sea roughies were imported from Japan. One died due to the stress of shipping, but the other two revived and were held in a quarantine system at 55 degrees F. All manner of prepared foods were offered, both free in the tank and on a feeding stick. Live grass shrimp and Gambusia fish were also offered. Neither fish reacted to any of the food items, but would navigate away from the feeding stick with an avoidance response. After one month, the fish were sedated and force-fed once per week, with feeding attempts made during the interim. After two and one half months, the fish were moved into a larger, darker exhibit in the hopes that this would make them feel more comfortable. The force-feeding was discontinued in the hopes that this would further reduce the fish's stress levels, yet the fish both continued to refuse to feed. At the point where it was determined that they were going to need to be euthanized, stick feeding was attempted one final time. By vibrating the food item in front of one fish, a slight feeding response was elicited. Eventually, the fish struck at the food, but missed. Additional feeding attempts were made and soon it was stick-feeding fairly well - fully five months after its arrival at the facility and 2 ½ months since its last force-feeding. The second fish observed the first fish feeding and it soon began stick-feeding as well. Within a month, both fish were feeding on broadcasted food items, and the amount even had to be reduced in order to avoid them over-feeding.

this_japanese_roughy_was_anorexic_for_months_but_now_begs_for_food_at_the_surface.jpg

This Japanese roughy was anorexic for months but now begs for food at the surface.

Large morays and wolf "eels", Gymnomuraena sp., Gymnothorax sp., Muraena sp. and Anarrhichthys ocellatus

Reports abound from public aquariums where these eels stop feeding for a week or two to months on end, and then spontaneously resume feeding with no intervention by the aquarist. There does not seem to be any seasonal or temperature relationship with this behavior. Wild-collected zebra moray eels, Gymnomuraena zebra are well-known for not feeding well when first brought into captivity. One specimen refused all food for nine months and then spontaneously began feeding on cut up seafoods, and never showed any appreciable loss of body mass. Two newly collected dragon morays, Enchelycore pardalis were imported from Japan. Neither would feed and one died within a few weeks. The other one spontaneously began feeding four months after its arrival and is perfectly healthy three years later.

adult_wolf_eels_often_refuse_to_feed_when_first_collected.jpg

Adult wolf eels often refuse to feed when first collected.

this_dragon_moray_refused_food_at_first_but_now_is_doing_fine.jpg

This dragon moray refused food at first but now is doing fine.

Orange-spotted filefish, Oxymonacanthus longirostris

As is typical for this species, the specimen would not feed on any normal aquarium foods until it was offered live colonies of small polyp stony corals. It fed very well on these corals, and even gained body mass. It became anorexic again when isolated from a source of live coral as a food item. This is not an example of chronic anorexia, but rather an inability to properly meet the fish's environmental needs.

Pacu, Colossoma macropomum

One specimen was reported to have stopped feeding for approximately four months at a major public aquarium. There was no discernible cause for this. After 12 days of daily tube-feeding, it began to feed on its own again and did not show any further signs of anorexia. Likely, an unidentified environmental factor caused this fish to suddenly stop feeding. In a similar case, a Moorish idol, Zanclus canescens had adapted well to captivity when it suddenly stopped eating. A bulge in its posterior abdomen indicated that perhaps the fish had a blockage in its digestive tract. Within a week, the swelling disappeared and the fish resumed normal feeding.

Pimelodid catfish, Sorubmimichthys planiceps, Pseudoplatystomafasciatum and related species

Large specimens of these catfish in public aquariums have been reported to go on fasts that can last four to six months. Many of these fish would spontaneously begin feeding with no apparent ill effects - and with no indication that they lost much body mass. As these fasting periods do not always coincide with a drop in water temperature, there may be some other seasonal factor involved. One aquarist hypothesizes that these fasts coincide with the long migrations these fish make during the spawning season, where they normally might not be able to feed normally. The same aquarists offers another hypothesis that these fish are so well fed in captivity that they periodically stop feeding because some physiological threshold is reached telling them they are building up too much fat, and must stop feeding.

Pinecone fish, Monocentris japonicus

A long term captive that had been feeding normally suddenly stopped feeding. After four months of anorexia, it succumbed. Necropsy results showed a huge amount of belly fat as well as a fatty liver. Freshly collected pinecone fish from Japan have been reported to refuse food for over two months before eventually beginning to feed on their own. Due to their armored bodies, it is difficult to ascertain if they lose body condition during these long fasts.

Red-rimmed batfish, Platax pinnatus

A large juvenile specimen was acquired and, as typically seen with this species, refused to feed any offered foods. After being tube-fed a number of times, it began feeding unassisted on live brine shrimp and baby guppies. A few weeks later, it succumbed to a massive external bacterial infection. This may be an example of while tube-feeding can give a fish needed food energy, the process itself can be stressful and the constant handling can damage the delicate skin leave a fish open to bacterial infections.

Saddleback butterflyfish, Chaetodon ephippium

A very large adult specimen was acquired, but refused all foods for four months in captivity. The fish did not seem to lose significant body mass during this period, and its behavior was normal in all other respects. It spontaneously began feeding on food items that had been previously offered and ended up living for a normal length of time.

Smooth butterfly ray, Gymnura micrura

Acquired as a sub-adult, the ray refused to feed unassisted for one month and was tube-fed for approximately five weeks until it eventually succumbed to physical damage caused by handling during multiple force-feeding events.

Snowflake moray, Echidna nebulosa

A juvenile specimen was feeding well, but then stopped feeding for seven months after jumping out of the aquarium and being found partially desiccated on the floor. It eventually began feeding, but then died one week later. This may have involved liver damage from the extended starvation. This fish did show severe emaciation and probably should have been euthanized, although force-feeding might have helped.

Stonefish, Synanceia verrucosa

A large adult specimen was wild-collected and transported to a public aquarium. It refused to feed for over 9 months, even when placed in an aquarium with other stonefish that were feeding normally. It did not appear to lose much body mass during this lengthy fast. One day it suddenly began eating food that had previously been offered, and ate normally after that time.

Tarpon, Megalops atlanticus

This species is typically only maintained by public aquariums, however pond raised juveniles have been made available to the pet trade (although highly inadvisably due to their huge maximum size (over 350 pounds)). Adult tarpon have been reported to cease feeding for months at a time with no apparent ill affect. Some of these cases seem correlated to lower water temperature during the wintertime, and may be a normal seasonal behavior for this species. A rise in water temperature, or a few months passage of time always seems to result in the tarpon's eventual resumption of normal feeding.

Conclusion

Be sure to evaluate a non-feeding fish right away and take steps to resolve any environmental problems. Don't fall into the trap of assuming the fish will begin feeding when it gets hungry enough, or conclude it must be eating something, just not when you are watching. A fish that does not actively pursue and consume food that you offer it is going to have problems surviving for the long term.

References

  1. Hemdal, J.F. 2006. Advanced Marine Aquarium Techniques. 352pp. TFH publications, Neptune City, New Jersey
  2. Hemdal, J.F. 2001. Tube feeding techniques for fish. Freshwater and Marine Aquarium 24(12): 50-58
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