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Fish Issue Case Histories – test your knowledge!
The following are a series of case histories regarding problems with aquatic animals. Each scenario results in a question as to how the particular event transpired. With the clues given, you can test your aquarium knowledge and reasoning ability by attempting to deduce the correct answer. Note that these cases were selected because they had a single answer for a single problem as opposed to more common event of multiple causes of a single problem, such as: “Help, all my fish died!” - With the answer being yes, that’s because you fed them too much, kept them in too small of an aquarium, didn’t have a filter AND mixed piranha with angelfish!
Try solving these cases yourself. Most of the solutions do not require an extraordinary knowledge about aquariums; just a decent grounding in aquatic science, plus the ability to extrapolate and synthesize information in order to deduce an appropriate solution. Like all good puzzles, some of the data presented is superfluous, but all of the necessary clues are included along with that extra information. The first few questions are rather easy to solve, but the complexity increases as you go down the list. See how far you can go before making a mistake. If you can solve most of these problems, then your aquarium knowledge is certainly sufficient to handle almost any husbandry problem you’ll likely encounter.
Case #1: You buy a pair of black mollies for your 10-gallon community aquarium. Three days after you put the mollies in your tank, you notice that they each have 10 or 15 white bumps on their bodies, each spot is the size of a grain of salt. Both fish are also shaking and shimmying, like they are chilled.
Answer: This one was sort of a “give-away”. Hopefully you’ve successfully identified this classic instance of freshwater “ich”, a disease caused by the ciliate protozoan, Ichthyophthirius multifiliis. The only danger here is if proper treatment is not begun soon enough. If you don’t already have an arsenal of ich medications in your possession, your local pet store can help you with supplies to quickly cure these sick fish.
Case #2: You net up a school of large tinfoil barbs in order to move them from one of your aquariums to another. While in the net, the fish thrash around quite a bit, and manage to lose a few of their scales. Aside from the missing scales, they seem to take the move very well. However, three days later, you notice that many of them have developed what looks like puffs of cotton wool growing out of their bodies.
Answer: The fish have developed a saprophytic fungal infection at the sites where the transport injuries occurred. Generally, this is a less serious problem than if the injured site had become infected with bacteria (which more commonly spreads systemically thought the fish’s body). Treatments might include common anti-fungal baths such as methylene blue, although if the case is relatively minor, it often resolves without treatment.
Case #3: Invited to a party, the host (knowing your experience with aquariums) proudly asks you to critique her aquarium. Looking over her 29-gallon, fish-only marine tank you see four fish; all are well fed and fairly healthy, but all are breathing very deeply and rapidly. The water is clear; the equipment consists of an undergravel filter running with two submersed powerheads, a heater and full glass top and strip light. The host remarks, “these marine aquariums sure can mess up a house with all that salt spray” but went on to say that she solved that problem by adding that glass lid and by switching from airlifts to a powerhead driven undergravel filter last week. You remark that the tank looks pretty good, but that there may be a problem (as you measure the respiration rate of a yellow tang at 200-gill beats per minute, almost twice the normal rate). You ask the host what the water quality is for the aquarium; temperature 78 degrees, pH of 8.0, no ammonia or nitrite and the nitrate level is 25 mg/l nitrate-nitrogen. No new fish have been added to the tank in over a year. Why were the fish breathing rapidly?
Answer: The evidence in this case was the recent addition of the glass top and the replacement of the airlifts with submerged powerheads. While there was good water circulation, the gas exchange was very poor because no bubbles were breaking the surface tension of the water – and this was holding high levels of dissolved carbon dioxide in the tank. Within 15 minutes of adding a standard air-stone to the tank, the yellow tang’s respiration rate dropped to a more reasonable 120 beats per minutes.
Case #4: A group of Caribbean reef fishes are acclimated to a 900-gallon quarantine system. Rather than using a standard copper quarantine protocol, it was decided to try using a long term, low salinity bath to quarantine the fish. The specific gravity of the system was lowered from 1.021 to 1.013 over three days. For the next 8 days, the fish seemed fine – eating well and behaving normally. On day 9, some of the fish were seen with raw red patches on their skin, cloudy eyes, eroded fins and rapid breathing. By the tenth day, a few of the fish had died, and now all were showing the same symptoms. What was affecting the fish, should antibiotics be added?
Answer: Microscopic examination is needed to confirm this, but what looked like a massive bacterial disease was a protozoan infection. The low salinity bath quarantine is designed to reduce or eradicate many common parasitic protozoans such as Cryptocaryon. However, one protozoan of the genus Uronema thrives in lower salinity water. It is unfortunate that the symptoms of Uronema infections are almost always mistaken for that of a massive bacterial infection. This generally prompts the aquarist to begin antibiotic therapy, which of course is useless, and many of the fish end up dying.
Case #5: A group of 30 very rare fish from remote Ascension Island arrived via Air Cargo and were acclimated to a 600-gallon concrete tank filled with seawater. As this was an unexpected shipment, the aquarist had to put together a filter system in a hurry. A pressure sand filter with active bacteria was removed from another system and quickly connected to a one horsepower centrifugal pump using flexible PVC hose and soft rubber couplers attached with hose clamps. The filter’s intake and return lines were placed underwater in the tank, and the pump was started up. Later, after an uneventful acclimation procedure, all the fish looked fine, some were even eating. However, the next morning, all 30 of the fish were dead except one sickly damselfish found hovering beneath a clam shell at the very bottom of the tank. A few of the deceased fish showed mild bilateral exophthalmos (pop-eye involving both eyes) but all of them had unusual silver colored “lines” in the clear portions of their fins. Why did they all suddenly die except for the single damselfish?
Answer: The hose clamp holding the intake hose to the pump body had not been tightened properly and an air leak developed on the suction side of the pump. This resulted in super-saturation of gas in the water. The filter’s output (effluent) was held below the water level, allowing the water that was supersaturated with air, to flow unimpeded into the tank. This gas then came out of solution in the fish’s blood stream. The silver lines in the fish’s fins were simply air bubbles. The damselfish survived by hiding beneath a shell where the partial pressure of the gas was lower due to a lowered diffusion rate around the edges of the shell. Although this problem is most commonly seen when industrial pumps are used, even hobbyist-sized equipment can cause gas super-saturation if improperly installed.
Case #6: This problem is more within the realm of public aquariums, but a good problem-solver must be able to adapt to diverse conditions: An aquarist installed a 120 volt, ¾ hp chiller and a circulating pump on a 500-gallon insulated polyethylene vat in preparation for using it as a cold-water reservoir for performing water changes on cold marine exhibits. He installed the pump and chiller, and submersed the thermostat sensor in the vat and plugged everything in and watched as the vat’s temperature began dropping towards the target of 50 degrees. A week later, the aquarist asked to submit a work order because the chiller was malfunctioning. Asking him for the details, he remarked that the chiller was running all day but even though the thermostat was set for 49 degrees, the water temperature never went below 54 degrees. He went on; yesterday morning when he came in, the chiller was working so hard it had iced up even though the temperature of the vat was only 65 degrees. He commented that it was like that every day – in the morning, the vat temperature was very warm, but it dropped during the day – sometimes to as low as 56 degrees by the end of the day. The next morning though, the temperature was always above 65 degrees. The curator came up with a solution that took about 30 seconds to implement.
Answer: The curator simply asked the aquarist to plug the circulating pump into a different circuit. Although the chiller was hard-wired into the building’s main power grid, he had plugged the circulating pump into the same circuit as the building’s overhead lights – a circuit which was turned off every night at 6 p.m.! Each evening when lights, (and the pump!) turned off, the water in the vat began to warm up. Since the chiller’s thermostat was submersed in the relatively warmer water of the vat, the chiller iced up at night as it tried in vain to cool that water. Each morning, when the lights were turned back on, the pump started along with them. So, during the day, the system seemed to be working fine as it gradually began to cool the water in the vat. Just as soon as the lights went off again that night, the process started all over again.
Case #7: You’ve added a group of quarantined surgeonfish to your large reef aquarium in order to control unwanted algae. After some initial squabbling, the two Acanthurus pyroferus, a Ctenochaetus hawaiiensis and a Zebrasoma xanthurus begin co-existing quite well. Other tank-mates include three Valenciennea strigata and a Parupeneus barberinoides. A few months after the tank is established, the surgeonfish are more than taking care of the unwanted algae; in fact, you need to begin supplementing their diet with dried Nori in order to keep them satiated. This added food caused yellowing of the water, so you added activated carbon to remove that. After a few months, you notice that the Zebrasoma xanthurus has damaged fins. The other fish in the tank look fine, but this fish has big notches missing from its dorsal, caudal and anal fins. It almost looks like semi-circle bites have been taken out of trailing edges of fish’s unpaired fins. You have not seen any of the other fish chasing it. What is wrong?
Answer: Don’t be misled by all these scientific names, they were mostly used as a ruse to make the problem seem more difficult, and to throw you off track. Your first reaction might first be to look up all these scientific names in order to figure out their common names so you can determine what other fish in the tank might have begun attacking the three surgeonfish. The fact that the Purple tang, Zebrasoma xanthurus has the issue is key. This species is known to be highly territorial, so it should not be the one being attacked by the other fish. Note that the problem did not arise until after the tank’s algae growth had been all but eliminated, and the addition of dried Nori to the fish’s diet was made (A fairly drastic diet change). However, the true culprit was the addition of activated carbon to the system. Zebrasoma surgeonfish do not show typical symptoms of Head and Lateral Line Erosion, rather they turn a bit pale, and their unpaired fins develop scalloped margins.
Case #8: A large aquarium was designed to house a school of up to twenty adult red-bellied piranha. A compatible group of sibling piranha were acquired, quarantined and added to the exhibit. No fish were lost during the first year. Towards the end of the second year, one of the fish was found half-eaten by its tankmates. The feeding rate for the tank was increased, (their diet consisted of a mixture of previously frozen smelt, capelin, squid, shrimp and herring) but every month or so, another piranha was killed and eaten by its siblings. Eventually, only one fish remained. This scenario was repeated with a second group of piranha over the ensuing few years. With the third group of piranha, a dietary supplement was added which solved the problem and allowed this group to co-exist peacefully for many years. What was the supplement?
Answer: Thiamin was added to the frozen seafoods, which were fed to the piranha. Some types of seafood are high in the enzyme thiaminase, which destroys much of the naturally occurring thiamin. Thiamin deficiency in piranha manifests itself in cannibalistic behavior.
Case #9 A group of four, fully quarantined garden eels were established in a 30-gallon aquarium with an undergravel filter covered by 8” of crushed coral and fine coral sand. The undergravel filter draws water from beneath the filter plate through a bulkhead fitting in the bottom of the tank, up an external airlift tube at one end of the tank, and back into the aquarium through another bulkhead, at a right angle to, and just below, the water’s surface. The eels readily fed on frozen mysid shrimp and plankton swept past their burrows by the flow of the filter’s effluent. After a few months, the sand had compacted enough that the flow through the filter bed was diminished by about 50%. By measuring the remaining output of water from the lift tube, it was determined that although the flow had lessened, it was still more than enough to maintain proper biological filtration. Indeed, the water quality parameters were never less than optimal for this species. Over the following few months, the garden eels gradually stopped emerging from their burrows, and subsequently stopped feeding normally. One eventually died of malnutrition, while the remaining three were severely emaciated. What went wrong?
Answer: The only real defense garden eels have against predators is to retreat into their sand burrows. They are most vulnerable while partially emerged from their burrows while feeding. Therefore, they only risk feeding when there is enough food available to make the risk worthwhile, as when tidal currents are flowing strongly, bringing the food to them. During slack tide, when the water isn’t flowing, food is not as prevalent, and the risk of being eaten is greater than the chance of getting enough food, so the garden eels hide in their burrows during that time. As the sand filter bed became compacted over time, the flow rate through the lift tube lessened. Finally, the current in the tank diminished to the point where the eels “felt” it was slack tide – time for them to stay down in their burrows. As long as they stayed there, they wouldn’t feed, and they gradually began to starve to death. Since the undergravel filter was still operating well enough to permit adequate biological filtration, the solution to this problem was to install a powerhead in the aquarium, adding to the circular flow of water. Within a few hours of adding the powerhead, the eels emerged from their burrows and began feeding normally.
Case #10: A juvenile Pomacanthus imperator has been doing in your tank for five weeks. It gradually began to develop tattered fins, rough looking skin and now it has cloudy eyes. It’s still eating o.k., and not breathing too fast. Does it have a bacterial disease?
Answer: No, this species of angelfish is very susceptible to Neobenedenia flukes. All fish in the aquarium either need to be treated with multiple praziquantel doses (up to 5x, spaced 7 to 8 days apart) or moved to a hospital tank and treated with hyposalinity (half salinity in this case; 1.012 or 16 ppt) for 30 days.
So, how did you do on these exercises? Give yourself 10 points for each correct answer. There isn’t really any “passing grade” for this exercise, but there may be a general trend that each 10 points that your earn equates to about a year of active aquarium keeping experience. Remember that “Practice Makes Better”. Practice never “makes perfect”, but if you work hard, you’ll gradually improve your skills. Test yourself often; learn all that you can, sharpen your reasoning skills, so that when your aquarium animals decide to test YOU, you’ll be better able to solve their problems.
If you want to try more applied knowledge tests, there is a clinical case workbook that contains over 200 cases prepared by a veterinarian:
Lewbart, Gregory A. 2017, Self-Assessment Color Review: Ornamental Fishes and Aquatic Invertebrates 2nd edition. CRC Press.
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