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Solving Mysterious Deaths In Your Aquarium

by Ruby Bayan - 01/23/06

Rock Cave "Help me! It's my fish! I just fed them this morning, none of them looked sick. Now they're dead!" Bob's voice quivered over the phone.

"Take it easy, Bob. I'll be right there." You rush to your friend's house to find him sobbing over the coffee table where two of his favorite Oscars lay dead on a paper towel.

You examine the fishes -- there are no indications of disease. No white spots, no reddish lesions, no parasites attached, and no hole in the head.

"I was gone for just a couple of hours." Bob explains. "When I got back, they were..." he chokes.

You know Bob to be especially fond of his fishes and had been successful in raising his Oscars for quite a while now. This is clearly one of those "mysterious death" cases -- a challenge, surely, but not impossible to solve.

"I'm sorry about your Oscars, Bob. Just relax and let me look around if I can determine the cause of death -- maybe find the murder weapon. This will have to be a crime scene investigation." You get excited at the prospect of solving a mystery. Bob can only hold back his tears, comforted by your presence and concern.

Examining the Scene of the Crime

You approach the 50-gallon aquarium and give it a close look. The first thing you eliminate as the cause of death is incompatibility. Bob had no other fishes in the tank that could compete with the Oscars. You spot three Siamese Algae eaters doing their thing among the plants in the background. They couldn't possibly have harassed a couple of 4-inch Oscars to death.

Oscars this size are still relatively juvenile, so, they obviously didn't die of old age.

Could it have been lack of oxygen? Certainly the tank is far from being overstocked, so you look for decaying food and rotting debris that could sap the oxygen level. The tank looks impeccably clean -- for an Oscar environment. Bob had been taking care of his fishes well.

The next thing you check is the decor. Bob can be extra creative with his decor. Had he also been safety-conscious? You've seen him experiment with electric blue substrate and sleepy-hollow-type driftwood, so you want to check out how innovative he has been with the decorations in what is now the scene of the crime.

Could one of the rock pile formations toppled over and hit the Oscars while they frolicked underneath? Could the fast-growing fishes been accidentally stuck in a hole or crevice? Are there any sharp or pointed formations that could've caused a fatal concussion on the highly active couple? You look through the front, side, and back of the tank -- negative on all counts.

Signs of Breaking and Entering

You turn to Bob, his gaze frozen on his dearly departed pets. "They look like they're just sleeping," he whispers.

"I need to ask you a few questions, Bob. Are you up to it?"

"Sure. Ye." Bob raises his eyes for just a second, and takes a deep breath.

"We're going to try and eliminate the possibility that contamination or the introduction of something toxic caused your Oscars' death." You proceed with the investigation, trying to sound very professional.

"Did you recently medicate the tank?" Malachite green and methylene blue are common medication for parasites and fungus, but extended use or an overdose can also kill the beneficial bacteria that help maintain the ideal environmental conditions in the tank. The death and absence of the bacteria can lead to an ammonia or nitrite spike that kills fishes in no time. Bob said he has had no need to administer any type of medication.

"Did you bring in new fishes that you failed to quarantine before including in the tank?" Newly bought fishes come from "unknown" environments -- although looking healthy, they could be contaminated with all sorts of microorganisms and parasites that could unleash a fatal and unpredictable epidemic. The same is true with the water the new fishes were transported in.

Bob assures you he always quarantines new fishes, and the newest one he put in that tank was a couple of the algae eaters, several months ago.

"Do you have sick fishes in your other tanks?" Bob has two other tanks and you're wondering if he has sick fishes in there. Because if he does, he should not be sharing nets, scrapers, decor, and equipment between sick tanks and well tanks due to the risk of contamination. He should even be washing his hands well after doing any form of maintenance on hospital or quarantine tanks.

"Nobody has been sick lately. I've been very careful with contamination," Bob answers, almost resenting your insinuations.

"Did you just do a water change?" You're thinking it's possible that Bob may have done a considerable water change and he may have forgotten how much chlorine the tap water has. High concentrations of chlorine attacks the fishes' gills and can cause death due to asphyxiation.

Before you can follow up on that question, Bob shoots back with, "The last one was five days ago, and, yes, I always make sure the new water has no chlorine, and has the same pH and temperature as the water in the tank." Okay, so that's out of the way.

"Would you mind if I look at your supply of fish food?"

Bob points to the side of the stand where he keeps his containers of flakes and pellets. "The frozen food are in a covered plastic container in the freezer," he adds. You check the expiration dates on all of the labels, and examine the food for molds or unusual appearance. Even the best fish food can turn into something lethal. You ask Bob if he trusts his live food vendors -- he swears by them.

You give the tank a second look for anything potentially toxic to the Oscars. Could Bob have introduced a new decor that he failed to clean? Is any of the stuff in his tank water soluble or metallic? Once again, nothing raises suspicion. It's time to test the water.

The Lab Reports

"Where's your water test kit, Bob?"

As Bob pulls out his kit, you glance quickly at the tank's thermometers -- one close to the surface at one end of the tank, the other submerged close to the bottom at the other end. Both of them read 75 degrees.

Meticulously, Bob arranges his testing paraphernalia and volunteers to check the water himself. He starts with the pH. Because his tank had been long established, he expects the pH to be a little below the neutral 7.0. A high reading would indicate the possibility of high and toxic ammonia content. The pH test reads 6.5. And the ammonia level comes out normal (below .3 mg/liter), which is expected because if ammonia had been high, the water would've had a yellowish tint and given off a pungent smell.

How about nitrite or nitrate poisoning? In ideal conditions, the ammonia released by fishes through respiration and excretion are converted to nitrites (by beneficial bacteria), which are then converted to nitrates (also by beneficial bacteria), which are then absorbed by plants as fertilizers. Nitrates become toxic above 100 mg/liter, but this shouldn't happen if Bob had been doing regular water changes.

Nitrite poisoning ranks high in the list of culprits for the Oscars' death because it kills almost instantly and its victims die in full color. When the oxygen supply in the water becomes insufficient, brought about by overstocking, overfeeding, decaying food and debris, and improper filtration or aeration, nitrites are not converted to nitrates. At nitrite levels of higher than 10 mg/liter, the water becomes toxic to most of the fishes.

"If it's nitrite poisoning I have only myself to blame," Bob sighs. Afraid of the truth, he makes you conduct the test. Result: normal. You hit another dead end.

More Poisons

You widen the area of inspection and look around the room for any telltale evidence of another kind of poisoning -- biohazards.

Toxic fumes dissolve in water and although a bit remote, it can accumulate to a level deadly enough to the residents of an aerated aquarium.

"Has anyone come in the room to clean?" You ask Bob who looks more composed now.

Bob looks at you and glances around what he always refers to as his domain of organized chaos. "Does it look like someone came in to clean?" He drops a hint of sarcasm.

"I'm just wondering -- someone may have used an aerosol detergent or glass cleaner pretty close to the tank. Those wood shine sprays, furniture cleaners, and carpet deodorizers can contain toxic chemicals, you know. You sure you didn't use them lately then submerged your hand in the aquarium? Just want to be sure."

Bob gives you the what-the-hell-are-you-talking-about look. So, instead of asking another question, you just make a mental note that he doesn't smoke and it doesn't look like paint fumes is a suspect. You move on.

"Do you know if you have copper plumbing? I read that copper poisoning is a real threat to fishes. Copper is sometimes used in medicines to fight snails and algae. And copper pipes can contaminate tap water." You just want to cover all the bases. Bob says the house was built just two years ago and he doubts they used copper pipes for plumbing. He's never had to deal with snails or treat algae with chemicals.

"There wouldn't be copper or other metal ores in your rock decor, would there?"

"Are you kidding?" Bob says. "Those rocks are inert -- hard plastic. Looks real, huh?"

You're running out of options. But there are still a few things you haven't explored. You wanted to save it for last because you're hoping you wouldn't have to confront Bob with the idea that he had been killing his fishes very slowly for the longest time.

Slow Death

When humans suffer from stress, anxiety disorders, and unrelieved tension, their immune systems malfunction and the end result is mayhem of disorders such as headaches, muscle pain, poor coordination, depression, and a nervous breakdown.

Fishes are also highly susceptible to stress that weakens the immune system. It's possible that prolonged exposure to stress is the root cause of the sudden, yet inevitable, death of Bob's Oscars. You want to know what could possibly have been stressful to the fishes. You start ruling out the obvious.

"You haven't been moving the fishes around, have you?" You sit beside Bob and join him in staring at the tank that now looks so empty.

"Nope." Bob answers quickly. "I've been tempted to hold them -- they're very friendly. They come to me when I approach the tank. They know when it's time to feed them. But I've never held them. I'm afraid I'd hurt them."

You noticed the wide screen TV and audio system across the room. "You know that fishes are highly sensitive to vibrations, right? You think your entertainment center gives them a headache?"

Bob looks at you with one raised eyebrow. "Come on, I deliberately put the TV and stereo across the room because I had learned my lesson. When I was younger, my bedroom was just half of this. I had to put my cassette player next to the aquarium. I wondered why my fishes never lasted more than a month. Then I noticed that every time I turned on the player the fishes darted around frantically. I did a little research and discovered that the vibrations of sound waves are four times 'louder' through water than through air. Therefore, loud sounds, tapping the aquarium walls and tank stands, and even slamming doors and windows can shock fishes out of their wits. I had been careful since then."

"Speaking of shock," you proceed, "fishes don't like sudden changes in anything. Has your water temperature been constant?"

Bob is eager to fill you in on how good a fiskeeper he has been. "I always check the water conditions. I check the temperature maybe three times a day. I know that fishes are delicate creatures and maintaining an ideal environment is extremely important because unlike in the wild, the aquarium is a small, enclosed habitat that could easily go foul if unattended. I am not aware of any equipment malfunction or power failure that could've caused extreme conditions in the tank."

"How about your feeding routine?"

"I was getting to that." Bob continues. "Nutrition is very important to fishes. Not just the right kind of food but also the proper manner of feeding. I give my Oscars a good variety of food, and in adequate amounts so they don't become obese. I read the labels, too, to be sure I am providing them with all the necessary nutrients. I don't want them suffering from some vitamin deficiency. And I never give too much too soon, especially if it's a new type of food because they can get constipated that way. Constipation can kill, you know. But I'm sure that's not what killed my Oscars." Bob buries his face in his hands.

"Your water changes have been regular?" You explore another cause of stress.

"Yes," Bob mumbles through his fingers. "Fifteen percent, every two weeks, conditioned water, like clockwork."

Once again, you're back to square one.

Lethal Weapon

You approach the coffee table and inspect the dead Oscars. You pick up a pen and flip one of them over.

Bob notices you and snaps, "Oh, no! You're not thinking of doing an autopsy on my pets are you?"

You leave the Oscars and reassure Bob. "I may not have to."

You rush back to the tank and trace the wiring of the lights, pumps, and heaters back to the wall socket. You notice that the socket doesn't have a GFCI or Ground Fault Circuit Interrupter. You unplug all the equipment and examine them one by one. Is any electrical part of the powerhead filter submerged in the water? Are the wires in the overhead reflector lamp properly insulated? They're all clean.

You pull out the heater that's camouflaged behind one of the rock formations, and… "Voila! Here's your culprit, Bob. Hairline cracks on your heater. Your fishes were electrocuted."

"How can that happen?" Bob looks over your shoulder, mystified.

"Your rock formation may have accidentally pressed on the heater and cracked the glass casing. The water seeped into the cracks and caused a short. Normally the short would trip a GFCI if you had one, but since you don't have one, you may want to check your house wiring because it should've tripped your breaker fuse.

"The short in the heater caused an erratic current to run through the water. The Oscars were in close proximity to the heater when the current surged, and the electricity flowed through their bodies, killing them instantly. If you had been there and dipped your hand in the water, you would've been zapped as well."

Bob falls back in the chair. "You mean because I didn't have that grounding interrupter thing my fishes and my own life were in danger all along?"

"Yep. Not just your Oscars but also you would've been toast. And it would've caused an electrical fire, too."

"How did you figure it out?" Bob wanted to know what tipped you off.

"When strong electricity runs through the body of a fish, it snaps the fish's vertebra causing instant death. When I flipped one of your Oscars, I noticed that it was limp, like it had a broken spine. That's what led me to your wiring. Case closed."

Bob thanks you for your help and condolences, and invites you to the funeral services at sunset. You put your arm around Bob's shoulder and offer to help him check the house's electrical wiring; that should be a lot simpler than solving the mystery of what causes healthy-looking fishes to swim away to that great aquarium in the sky.


Top 20 Suspects in Mysterious Deaths:

  1. Incompatibility - fish could harass each other to death
  2. Lack of oxygen - asphyxiation is just one of its many complications
  3. Overfeeding - leads to pollution, obesity, and other problems
  4. Decaying food and debris - raises the level of toxic chemicals
  5. Décor accidents - fish bruised, crushed, snagged, or punctured for art's sake
  6. Toxic or unsafe décor - unwashed, metallic, or contaminated
  7. Medication - read the fine print for the side effects
  8. Contamination - from sick fish, polluted water, infected tanks, or rotten food
  9. Chlorine poisoning - attacks the gills, and gags the fish
  10. Ammonia poisoning - like swimming in a pool of pee
  11. Nitrite poisoning - breathing in an alien atmosphere
  12. Copper poisoning - nobody survives a diet of metals
  13. Toxic fumes - they dissolve in the water
  14. Improper or inept handling - can injure externally and internally
  15. Sudden changes - not for the faint of heart
  16. Equipment failure - like pulling the plug on a life support system
  17. Loud vibrations - killing softly with loud songs
  18. Poor nutrition - a form of torture
  19. Constipation - can distress a fish to death
  20. Electric shock - just one zap and it’s all over

Suggested Reading:

Handbook of Fish Diseases

A Commonsense Guide to Fish Health

Colorguide of Tropical Fish Diseases

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