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Substrate Ingestion by Tank Occupants

Adrian Lawler, Ph.D.
(retired) Aquarium Supervisor (l984-l998) J. L. Scott Aquarium Biloxi, Ms 39530
Original to Aquarticles

Introduction
   Planned ingestion
Geckos, various lizards, tortoises, fresh water turtles, sea turtles, frogs, snakes, birds, hamsters, various fishes, and other organisms may ingest substrate in the enclosures in which they are housed. In addition to the accidental ingestion of substrate, various animals ingest substrate to obtain calcium, to aid in buoyancy regulation, and to help grind up food; some people even speculate that various animals maybe ingest substrate because they are "bored."

Some animals eat substrate seeking calcium for their diet. (http://www.thegeckospot.com/leohealth.html)

"Lizards have a very simple and elongated stomach. Some species are known to voluntarily consume rocks to help grind food within the stomach. ...Sea turtles are also known to consume coral." (http://www.angelfire.com/al/repticare2/page8.html)

"Stones are commonly found in Steller sea lions' stomach from pebbles to stones up to 12 cm in diameter! Scientists are not certain if these rocks are swallowed by accident or if they serve a useful function. It is speculated that they might help grind up fish, or act as a ballast when diving, or might help ward off hunger pangs when the animals are fasting on shore." (http://www.vanaqua.org/education/aquafacts/stellers.html)

"Sometimes, crocodiles swallow stones to aid in digestion or to add weight so they can stay underwater for longer periods of time. (The average croc has 10 to 15 pounds of stone in its stomach.)" (http://animal.discovery.com/fansites/jeffcorwin/carnival/lizard/estuarinecroc.html)

   Accidental ingestion
Snakes may ingest substrates of styrofoam pellets, wood shavings, ground corn cobs, etc., while in the process of ingesting their food. Such items may either stick to the prey, or be accidentally surrounded by the snake's jaws while eating. From my experience, such things ingested were passed, or caused no obvious problems.

Various other animals ingest sand to various-sized rocks. "Some turtles ingest rocks, from sand grain size to whatever will fit into their mouth. Some turtles get intestinal blockage because of it. Even sand can accumulate and eventually turn into a plug that needs to be surgically removed." (http://www.petstation.com/waturtl.htm)

Some fish inhale their food with suction created by the mouth and gill flaps. (http://www.geocities.com/Heartland/Plains/3515/food.htm) These fish may have problem with substrate ingestion. "Most ingest their food with sucking action that can be downright explosive--with prey literally vanishing in the blink of an eye. Fish accomplish such feats by creating powerful vacuums inside their mouths, springing them open like hydraulic traps in the presence of food,..." (http://www.research.fsu.edu/researchr/winter95/features/fish.html) Such suction can also pick up substrate, which is then ingested along with the food item.

Ingestion of substrate, if it does NOT cause impaction, or irritation and infection, is not a major problem. Some animals can pass the substrate ingested.

Some related information for tank occupants
Here we are talking about the accidental happenings of substrate ingestion, AND the deliberate ingestion of substrate to assist in regulation of buoyancy (as with tadpoles and crocodiles, etc.), or in grinding of food (as with crocodiles, various birds, etc). Any ingestion of too much substrate can lead to impaction of the gut, which can lead to death.

"Although these situations are indeed rare, the potential is there and some keepers choose some of the other substrate options to play things on the safe side, as turtles do have the tendency to eat gravel." (http://www.austinsturtlepage.com/Care/care.htm)

"Sea turtles are also known to consume coral." (http://www.angelfire.com/al/repticare2/page8.html)

"Larger seahorse species as well as the sea dragons are particularly at risk for foreign body (usually substrate) ingestion…" (http://seahorse.fisheries.ubc.ca/pdfs/PS_Husbandry_Manual.pdf)

"Substrate ingestion has a profound effect on gas-free specific gravity and larval anurans have evolved a mechanism to regulate buoyancy." (http://apt.allenpress.com/aptonline/?request=get-abstract&issn=0045-8511&volume=005&issue=01&page=0188)

In aquarium maintenance the tank substrate usually consists of sand, crushed coral or shell, or various types of crushed rock. Other substrates could be various-colored rocks, marbles, shells, etc. Some fish ingest this substrate via suction when they ingest their food, as noted above.

Personal experience, and discussion
On June 21, 1993 a small (5" TL) cobia (Rachycentron canadum) was added to a 210 gallon tank. On August 17. 1993 the abdomen was noticeably enlarged, but the fish was still eating. On August 23 and 24, 1993 the coelomic cavity area was punctured and a cloudy fluid was expelled. The fish was dead on August 26, 1993; it was nine inches long. A necropsy by Lawler revealed a "ball" of coral (about 30 mm in diameter) in the intestine, just prior to the vent. The fish had been eating #4 sinking trout chow pellets, floating flake food, and cut-up squid and fish. The fish had ingested crushed coral (2 x 2 x 2 to 4 x 4 x 7 mm) when trying to apparently ingest the small trout chow pellets lying on the crushed coral substrate in the tank. The coral had passed through the digestive tract and jammed up into a "ball" at the anal sphincter. The intestine was greatly distended and irritated at the "ball" of coral. It is not known if the blocked intestine, or our punctures, or a bacterial infection, or exhaustion from trying to stay mobile with the heavy load of substrate, caused the death.

Ingestion of rocks leading to death has also been seen in red-eared slider fresh water turtles (Trachemys scripta elegans) and mud sirens (Pseudobranchus striatus). These animals ingested substrate while trying to eat small food items lying on the substrate. In both of these cases the problem was corrected for future tank occupants by deleting sinking trout chow pellets and changing to floating food pellets.

Signs of substrate ingestion, other than visual observations, can be fish that do not swim on an even keel, i.e., head may be up and tail down due to extra weight of substrate.

Turtles that ingest substrate can be recognized by their vigorous efforts in swimming in order to obtain air at the water surface, the extra weight of substrate in their gut dragging them down. Turtles that list to one side, or to posterior, may also indicate those that ingest substrate (but may also indicate one lung full of fluid, as with pneumonia).

In the cases we observed, the noticed ingestion of substrate led to death, and the resulting necropsy revealed the substrate ingestion and impaction problem. There may have been cases where some substrate was ingested, but the symptoms of ingestion not exhibited or noticed. Death was probably due to impaction (blocked intestinal tract), or an infection arising from the irritated and stressed intestinal tract.

Prevention
Options to avoid substrate ingestion, as per Lawler:
….Have large enough substrate so ingestion is impossible, or difficult. (This will decrease surface area available to filter bacteria in an undergravel filter and may thus affect efficiency of biological filtration.)
….Use substrate that is small and round (for easier passing).
….Cover substrate with small mesh netting to prevent uptake of substrate while feeding on the bottom.
….Supply mineral (calcium) blocks for tank occupants' mineral needs (so they won't ingest substrate seeking calcium).
…..Feed larger pieces of food than the substrate size (if food sinks).
.….Feed floating food.

Most fish inhale and swallow and should not be fed small sinking food items that are about the same size as the substrate to prevent substrate ingestion. Food items should be visibly much larger than the substrate, or floating.

If an animal is inclined to ingest substrate because it is "bored," has a calcium deficiency, is grinding food, or is adjusting buoyancy, etc., one may have to remove the substrate from the tank or move the animal to another setting.

Summary
Various animals ingest substrate to obtain calcium, to aid in buoyancy regulation, to help grind up food, maybe because they are "bored," and accidentally while ingesting food. Animals that inhale (use suction) and swallow their food, or try to pick up small pieces of food from the substrate, should not be fed small sinking food items that are about the same size as the substrate to help prevent substrate ingestion. Food items should be visibly much larger than the substrate particles, or floating. Mineral blocks with calcium should be placed in tanks.

Copyright 2005 by Dr. Adrian Lawler, Author Copyright 2005 by Howard Norfolk & Aquarticles, Internet Publisher
Author Information must remain with article.

Dr. Adrian Lawler, P.O. Box 48, Ocean Springs. MS 39566 U.S.A.