Inter-relationship between Pygocentrus and Serrasalmus

By Frank Magallanes - March 05, 2005

MATERIAL IS SUBJECT TO CHANGE DAILY - OPEFE DOES NOT RECOMMEND DOING THIS IN THE HOME AQUARIUM

The test fish

Science recognizes a symbiotic relationship between Serrasalmus marginatus (juveniles) and Pygocentrus nattereri. S. marginatus acts like a saltwater cleaner wrasse fish in that the picks parasites off P. nattereri (Sazima and Machado,1990 and L. N. Carvalho, et al. 2003). Little is known of another species from Peru, herein called Serrasalmus sanchezi if it does the same thing or just travels with the Pygocentrus species as a wolf in sheep's clothing. They are often captured together in nets and it is not unusual to find them mixed in public aquariums looking like their formidable opponents. David M. Schleser in his book, Piranhas, A complete Pet Owner's Manual, makes mention of keeping two of these species together at the Dallas Aquarium when he was curator. But that aquarium was 500 gallons!

Science knows that any Serrasalmus species will engage in fin biting of its own kind and other species. Very little is known about the inter-relationships between these 2 genera. What I hope to do here using aquarium conditions is record whatever behavior can be observed with 2 - S. sanchezi (approximately 4 inches TL and one (1) slightly larger) and one (1) Serrasalmus maculatus (approximately 4 1/2 inches TL) mixed in with an assortment of 14 - P. nattereri and P. cariba ranging in sizes 6 inches TL to 10 1/2 inches TL.

 For the purposes of this test, four (4) P. cariba are excluded from the test because neither S. sanchezi or S. maculatus is found in P. cariba natural range.

All of this will be observed from a 150g Ag Stock Tank. One corner of the tank will hold a pile of lava rocks arranged to give the Serrasalmus species an area to hide in should things turn aggressive. Water temperature fluctuates between 74-80F. A heater is being installed on March 25, 2005 to help stabilize the water. I expect that aggressive behavior will begin greatest when the temperature is highest. Water changes will be from the faucet which will also result in 3 to 4 degrees lower temperature until the tank water warms up to its optimum. Water changes are done every 4 to 5 days. This will be modified to every 2-3 days once all the fishes are acclimated.

THE TUB OBSERVATIONS

DISCLAIMER: A reminder to hobbyists who are reading this web page:  Do not assume that OPEFE or this writer is suggesting you try this type of test in your home aquarium. I am meticulous in watching the activity in the tub. Any suggestion that the fish are in real danger, I pull all stops to remove it, least it be killed or suffer irreparable damage to the fishes body.

THE TEST

March 5, 2005:

Since putting them both together a week ago both S. sanchezi have begun to regenerate their bitten fins from being kept together in close quarters. It is hoped after moving them in with the Pygocentrus, they will bite them when the need for fins is greatest. Fins are a renewable resource for Serrasalmus species. It is a basically harmless instance, unless of course, the fish bites past the stub into the flesh. The fins regenerate with a few weeks, thus it becomes like a cow grazing in a field of grass that continues to grow. There is inherent danger that the Pygocentrus species will eat the Serrasalmus species. But as of the date of this writing, no such thing has been observed.

March 15, 2005, 0811: 

The S. sanchezi has been seen swimming above the Pygocentrus species, finally taking a bite of the dorsal fin of one (1) P. cariba (6 inches TL). The fish turned its head to a 90 degree angle before striking the dorsal fin. The P. cariba attempted to swim away and the S. sanchezi did not let go until the fin was removed. The P. cariba then chased the S. sanchezi away. Also observed was S. sanchezi chasing the S. maculatus trying to bite its fins. While it is apparent the S. sanchezi does not behave overly aggressive with the Pygocentrus species, it does not tolerate S. maculatus presence. The entire Pygocentrus group stay within the center of the tub facing in opposite directions as if to ward away any unseen attack. The other species of S. sanchezi stays within the safety of the rocks, occasionally venturing out but is also chased by the more aggressive, slightly larger S. sanchezi.

The S. sanchezi will not allow the S. maculatus to be close to the rocks for protection. It is observed on a daily basis the S. sanchezi will chase the S. maculatus to the edge of the tub and back. Sometimes the chase will attract the attention of the Pygocentrus species. The S. maculatus uses the aerator bubbles to hide in the middle of the tub siding. Bites to the fins of both Serrasalmus are indicated (mostly on S. maculatus).

Sequence of photos showing whereabouts of the 3 Serrasalmus species. Temp: 74F. Photos by Frank Magallanes

March 18, 2005, 1345: 

The fishes are still doing fine. S. maculatus seems to have suffered more fin biting by the S. sanchezi. The maculatus has returned to its spot behind the aerator. All fishes were fed chopped night crawlers and both Serrasalmus species were seen eating it.

March 19, 2005, 1123:  

Fish photos were taken of S. maculatus and S. sanchezi biting fins. Included in this photos are S. sanchezi swimming with P. cariba. No losses as of yet between any of the species.

 Sequence of photos showing positions during swimming. Temp: 77F. Photos by Frank Magallanes

March 22, 2005, 0900: 

he S. maculatus was removed. It was suffering many fin bites from 3 S. sanchezi. The fish was put into a hospital tank so that it can recover and regenerate its fins. Another S. sanchezi was moved into the tub and now there are four (4) S. sanchezi with the group of Pygocentrus. The larger S. sanchezi have been biting the young ones (smaller by 1 to 2 inches). Most of the bites have been to the anal fin and the tail.

The photo to the left shows the larger S. sanchezi  next to the Pygocentrus species. The larger S. sanchezi swim with the Pygocentrus and no bites have taken place other than the sanchezi taking fin nips. P. cariba generally chase the smaller sanchezi. Much of the fin bites in the entire group test is centered between the Serrasalmus species and each other indicating that perhaps S. sanchezi is a solitary species with low tolerance of same species in their respective territory.

Driftwood was added to the tub and the S. sanchezi (which appear to be a surface species) began to hide behind the branches of the submerged portions of the wood. They would wait there until it was time to bite a piece of fin off each other by chasing. Often this chasing would take sanchezi through the mix of Pygocentrus. At no time has Pygocentrus shown any interest in Serrasalmus nor taken any aggressive action. Even when sanchezi would chase each other in quick, violent circles trying to bite each others tail fins above the Pygocentrus. One cannot draw a conclusion that Pygocentrus will not take the opportunity to bite S. sanchezi, but it is interesting nonetheless the apathy displayed thus far.

March 25, 2005, 2300: 

Plants were added to the tub on one corner next to the power heads and rocks. Bit fins are beginning to appear on the P. cariba, 1 ternetzi and 3 Pygocentrus. All were fish approximately 6 inches TL. From what I could see, much of the biting occurred from S. sanchezi as the Pygocentrus species moved into the rocky area where the 2 of the 4 S. sanchezi hide. The other larger 2 - S. sanchezi (5˝ - 6 inch TL) are either by the tree roots are swimming among the larger Pygocentrus. No aggressive moves have been seen by any of the larger Pygocentrus species towards the S. sanchezi. As stated previously, the only one's biting are the S. sanchezi at each other and the smaller cariba and ternetzi. Fins are regenerating on 3 of the S. sanchezi. The largest S. sanchezi has suffered no fin bites.

March 26, 2005, 2300: 

Since I created this pond (or pool) at the beginning of March, I thought by now the S. sanchezi and S. maculatus would be gone and eaten by Pygocentrus. Instead, I've had to remove the S. maculatus after it was severely bitten several times by the S. sanchezi. The fish is now recuperating and regenerating its bit to the stub fins. The only fishes that have suffered fin bites (as expected) have been the Pygocentrus and the S. sanchezi. Which suggests these critters are solitary. They spend the entire day (and sometimes night) chasing and biting each other. Even if one is across the other side of the pool. All it takes is for one of them to get close (there are 4 - S. sanchezi in the tub now) and the chase begins. 

Water temperature is at 79F. All photos by Frank Magallanes

Most of the bites have been to the anal fin. Those can be fatal should the bites get into the organs. For the most part, the S. sanchezi are ignored by the larger Pygocentrus. However the smaller ones (6 inches more or less) chase after the S. sanchezi if they get to close. Here are some photos to include the anal fin damage. You can also see how close these species swim with Pygocentrus. When the smaller Pygocentrus enter the S. sanchezi territory (which is the rocks and some of the tree limbs) the sanchezi wastes no time in driving the fish off or getting a fin meal.

March 28 0830 and March 31, 2005 1012:

The larger Pygocentrus are now showing signs of being bit. There continues to be chasing by S. sanchezi to each other. P. cariba (not part of this test) has been chasing the S. sanchezi. Part of this reason (my opinion) the fish sees the sanchezi as a direct threat, so must be chased down and killed. As I earlier stated S. sanchezi is not found in the same distribution as P. cariba. Anything that happens in this test should be excluded on behavior between these 2 species. No chases have been observed with P. nattereri. The southern P. nattereri (ternetzi) has also been doing some chasing but not as frequent as P. cariba. Only when the fish is bitten does it give chase. With the exception of the largest S. sanchezi, all others have bites to the fins; dorsal and anal.

Examples of S. sanchezi lurking and bit fins of Pygocentrus. Underwater photos by Frank Magallanes

April 4, 2005 2345: 

The tub was outfitted with some live lily pads. Some Tupper-ware containers with gravel was also placed in the tub with some more live standard aquarium plants. The smaller S. sanchezi have found their own private hiding places. One can observe them peering behind rock caves and roots. The 2 larger S. sanchezi continue to swim with the largest Pygocentrus, biting them for a fin meal at least 3 to 4 times a day. As noted above, all the Pygocentrus now have bites to the tail, dorsal, pectoral and anal fins. When the entire group is fed cut fish or shrimp, all the fishes participate in a feeding frenzy. It is noted however, that S. sanchezi tends to take smaller portions or bits of food, not whole chunks like Pygocentrus. Diet of the fins remains the primary food. Scales that are knocked off are also eaten. Nighttime does not deter these fishes from biting Pygocentrus. In low light, one can observe S. sanchezi positioning itself for perfect strike. While bit fins remains common for the small sanchezi, the larger one's are regenerating rapidly. Some pre-breeding behavior has been observed with S. sanchezi over the submerged plants, tail slapping common to such activity has been seen. The same activity is also becoming more common with Pygocentrus cariba and the southern P. nattereri (ternetzi). Temp: 79F.

April 5, 6 and 7, 2005 1440: 

On April 5th, I added another S. sanchezi, bringing the total to 5. The fish immediately sought cover among the rocks and within an hour, the fish was seen in the open being chased by other S. sanchezi and P. cariba. From the observations, its my opinion the fish was not familiar with established territories and was then chased. The original 4 S. sanchezi are still regenerating fins with the 2 largest still engaged in tail slapping near the plants. By next week I hope to place the 6th and final S. sanchezi in the tub. The larger Pygocentrus species are regenerating fins and now only the smaller Pygocentrus are being bit by S. sanchezi. I have made no decisions on whether or not it would be prudent to reintroduce the S. maculatus. Its my opinion these are natural enemies in the wild. S. spilopleura which is found in Peru and close genetic relative to S. maculatus provides some clues how the latter species relates to S. sanchezi. A slight increase in water temperature is recorded: 82F.

1910 hrs - The fish are settling in the for the night. All 5 S. sanchezi have been accounted for with 3 (smallest) having bites to all fins, 1 has a bite to the dorsal fin and the largest is pristine. 2 P. cariba are staying by the planted area and very dark in color. This planted area is within approximately 15 inches from the rock pile and roots where all the S. sanchezi retire for the evening. The largest P. nattereri stay in the open area of the tub where most of the current flow is found. 2 semi-large Ternetzi (approximately 7 inches) have been observed near some plant roots. They are very dark in color but because the tub water is tea colored, difficult to tell why they are there (if there is a reason).  They defend the area, but it remains unknown if it is territorial or more specific to other activity. Tomorrow a water change will be done. Its hoped the tea colored water will lighten up some for better observation. All other Pygocentrus species are normal in color. Earlier reports of S. sanchezi tail slapping have ceased.  This activity was on-going until 1611 hrs. The color of both was dark, almost black. If these are egg  scatterer's as reported by Braker (1960) and Ledecky (1966), then if any eggs are released they should be well protected by the plants and rocks. 

April 09, 2005 2340 hrs: 

The activity in the tub has become less active in that there is not the constant chasing that was evident for the last few weeks. On occasion during the day and mostly at night, one can see S. sanchezi chasing its same species. My best opinion is, the fish is defending its territory more than just trying for a fin meal.  More plants were added today and it is hoped that is the reason why its much calmer in there. It is obviously stressful for the Pygocentrus species in such a confined area. More so, having a fin biter like S.  sanchezi taking nips at them. Earlier today I tossed in a chunk (whole body minus organs and head) of a bullhead catfish. This was cleaned and frozen last week. It was observed that all the Pygocentrus attacked the chunk of fish and the S. sanchezi were seen to also participate in the feeding frenzy. Biting pieces along side their deadly relatives. S. sanchezi has pretty much established their homes among the tree roots and particularly rock caves. There are many such openings for them to  go into for safety and these fish make good use of it.

 The smaller P. cariba also make use of the caves. Sometimes, there are quarrels between these two species. But nothing serious YET! I stay vigilant should anything go wrong. The last thing I want is a piranha or pirambeba cut in half.

Underwater photos of plants and exterior view of 150g Tub. Photos by Frank Magallanes

April 12, 2005 2310 hrs: 

Sunday, April 10, I added 2 Plecostomus catfishes. I thought adding these fishes would help cut down on the algae growth, but I was not certain how the piranhas (particularly the S. sanchezi) would deal with this. The fish in size are approximately 2 1/2 inches TL, perhaps small enough to avoid the gaze of the piranhas as food. Yesterday I found 1 that was hiding and cleaning an area behind a couple rock pillars. High enough in the tub so that the fish will not attract to much attention. I have no idea if the 2nd Plecostomus is alive or hiding in another part of the rock and root areas.  In reviewing the S. sanchezi, they all seem to be regenerating fins except for 1 that his a bit of flesh bit into though no portion of it removed. Other than that, they all look fine and growing nicely. The Pygocentrus are regenerating fins as well except for 2 of the medium sized ones (ternetzi). They are still being bit by the S. sanchezi and it seems to be only when ternetzi ventures to close to the areas staked out by the S. sanchezi. Much of the fin biting has been in the early morning hours and towards the evening. That is when these critters are most active and prone to bite Pygocentrus. All the plants in the tub are providing shelter for the piranhas and have helped open a few more hiding spots, even for the smaller P. cariba. I have not introduced the remaining S. sanchezi yet as planned. Instead I will wait a bit longer before doing this. I want to see what area would be the safest for introduction so that the fish can establish itself quickly in a hiding spot. Water change was completed this afternoon and water temperature went from 79F to 76F. Usually by late evening (water changes are done in early afternoon), the temperature will be back to normal. 

APRIL 14, 2005 1245 HRS: 

Today, 5 White cloud mountain minnows (Tanichthys albonubes) were added to the tub for decorative purposes, hopefully not as food, but one never knows. pH was taken and measured at 6.6, water temperature 75F. A bit lower than normal, but attributable to the heater being moved and not replaced during maintenance. Water temperature should return to normal by this evening. Fin biting (as expected) remains constant between intra-species. A couple of the larger P. nattereri have suffered additional fin biting by S. sanchezi. From my observations it is when the Pygocentrus gets to close to the tree roots where 1 S. sanchezi in particular waits and stalks. Sometimes this fish will actually go into the main body of piranhas and find 1 particular piranha and bite it then quickly flee to its rooted area. Overall, the test is showing the consistency of fin biting behavior. The larger Pygocentrus have formed tight groups and do not allow the smaller Pygocentrus species to enter without quarreling. In my opinion, they are doing the same as some cichlid species do in defense posturing to ward off any body attacks by S. sanchezi. 100 feeder gold fish were also introduced (not a recommended food item) as dither fish. I wanted to see how the S. sanchezi would react to having a different food source. Surprisingly, S. sanchezi bit a couple goldfish in half, left the bodies to float around and went back to biting Pygocentrus fins. They basically ignored the feeders, choosing instead to focus on the larger predators. A few goldfish swam within inches of S. sanchezi and the fish ignored them. Even after several hours of this. The shoal of feeder goldfish then formed and began swimming in a circular pattern around the tub. Each time they passed over the large Pygocentrus, one of those species made an attempt to eat them. 

April 15, 1455 hrs:

There are fewer feeders today, probably 30 remaining alive in the tub. These mostly hide in the plant thickets. Water temperature is at 79F.

April 16, 0945 hrs:

While looking in the tub, I spotted two (2) - 3 inch TL P. nattereri eating the remains of an S. sanchezi. I have no idea which of the piranhas or pirambeba ate this fish. Certainly, it was one of the larger S. sanchezi I had in the tub and the one usually seen biting the P. cariba that are nesting near a cave. I have always feared this would happen, but not much more one can do other than pulling out the remaining S. sanchezi. But in order for OPEFE visitors to learn (and at the expense of losing more specimens), this TUB test will continue as scheduled and reported.

April 17, 2005 1030 hrs: 

Scattered eggs were seen along the bottom of the TUB along the plants and the nesting area where two (2) Pygocentrus nattereri (ternetzi) have been observed tail slapping and remaining side by side. I will attempt to take photos later today. 

April 20, 2005 2045 hrs:

I did search of the TUB the last few days to try and make a head count of the S. sanchezi. After losing 1 of them on the 17th, I thought it prudent to do this. The present count is 3 of 4 S. sanchezi still swimming and alive. I have not found the 4th member. It could be this fish remains among the roots and rocks or it was eaten as well. I don't know. All I can reasonably do without disturbing the entire tub is to continue to watch for it and do a recount at a more opportune moment. Presently, all the fishes are doing fine with little aggression. The S. sanchezi have now found their common areas and hardly venture from it. If they do, one or all the other members of this species attempt to drive it away. The largest of this species continues to swim on occasion with Pygocentrus, but lately it has been mostly seen with the smaller P. cariba. That seems unusual to me because of the past conflicts between them. For now, there seems to be no aggression. Many of the tattered fins on the Pygocentrus have regenerated. Only 1 of the 3 seen S. sanchezi has tattered fins, the other two are nearly completely regenerated. This one seems to be the smaller of the other 2. I'd still like to find that 4th S. sanchezi, to at least see what kind of condition it is in. The diet remains steady, with feeding of shrimp, cod or live fish every other day. Water changes remain constant every 3rd day with 10-15% removed and replaced. Overall temperature remains at 79F. I notice some of the lily pads have been bitten off at the stem, so I have some floaters without roots. I suspect, though not seen yet, that the P. cariba are doing this. I make this observation based on the fact the lily pad roots are nearest one area where P. cariba frequents and mostly at rest.

April 22, 2005 2000 hrs:

I fed the piranhas a diet of bluegill freshly caught. They were dead, but the group wasted no time in dispatching 5 medium (about 6 in TL) Lepomis species. As of today only 2 of the 4 remaining S. sanchezi have been seen. A water change was done because of the heavy feeding and I was hoping to see if the other 2 were still there. Remains unknown at this time. They use the root and rock covers and the 2 larger S. sanchezi stay out in the open. I moved the overhead lights to see if that will help in detecting where the other 2 might be hiding, assuming they are still there. I still have no plans in re-introducing the S. maculatus into the tub. At this point with the S. sanchezi still present, it would likely lead to fighting and biting. At this point, I think its wise to again remind hobbyists: A single catfish (Plecostomus) was seen (there are supposed to be 2). Since these fish are simply there to clean up excess algae, they are not a focus of this test. I will however, mention them when I see them. Same goes with the 5 still remaining White Cloud Mountain Fish. A small shoal of gold fish still remain (about 6 or 7 of 100).

April 23, 2005 1500 hrs:

While cleaning the filter pads, I discovered the missing 3rd S. sanchezi. The 4th S. sanchezi is probably hiding under the deeper area of the TUB and has not come out to plain view yet. Water temperature is at 78F. Also seen, the white cloud mountain fishes (Tanichthys species) were doing what appeared to be laying eggs among the longer strands of hair algae on the rocks. They made repeated moves that at best could be described as serpentine movements with the bodies very close together. Certainly it was a male and female as these fish are sexually dimorphic. An unexpected surprise.  I'm hoping that the 4th S. sanchezi will surface during feeding time. I will be watching for it. All fins on the Pygocentrus continue to regenerate, with no new clipping seen. Most of the bites on the fins seem to be directed at the smaller S. sanchezi (3rd species) and could explain why the 4th S. sanchezi stays hidden from its larger kin. Also, not seen is the 2nd young (3 inch TL) P. nattereri. I don't know if it was eaten or just hiding. The one currently seen is gross in weight, evidently feeding well.  Certainly growing rapidly.

April 29, 2005 1322 hrs:

A check over the last few days regarding the missing 3rd and 4th S. sanchezi has confirmed my fears. Both smaller fish are gone now. All that remains are two (2). One is the largest S. sanchezi (pristine condition) and one a tiny bit smaller (with nip fins on the tail, dorsal, anal, and pectoral) in length. Conditions in the TUB remain consistent with fin nips continuing on all species after a period of bite suppression. Only 1 young P. nattereri remains alive. The 2nd one has not been seen in weeks, probably also eaten by the larger Pygocentrus. Water temperature has been allowed dropped to 74F over a period of a few days. 

May 1, 2005 1030 hrs: 

Several hundred fry were found among the plants in the TUB. A handful were collected and placed into a 5 gallon aquarium. Sponge filter and heater installed, temp 77F. 

May 7, 2005 0930 hrs:

I noticed the smaller S. sanchezi very bit up and appeared the tail was eaten away. I tried to remove it but it hid in the rocks. I could not see much else to do except leave it there until another opportunity to catch it.

It didn't look in very good shape at all. The larger S. sanchezi is doing fine so far.

May 9. 2315 hrs:  

I finally saw the injured S. sanchezi. As I turned to get the net to take him out the entire group of P. nattereri attacked it. There was no time to save it. I watched helplessly as the group ate the fish. It took just a few moments and it was gone. I plan to remove the last remaining S. sanchezi in the morning. I will report how that went and place it here. As of now:

THE TUB TEST IS CONCLUDED.

Please read the SUMMATION below..

Summation

It is my opinion the TUB TEST using a mix of Pygocentrus and Serrasalmus failed for several specific reason's:

1) Serrasalmus species are fin biters and practice stealth using this to bite the fins of other prey including their own kind.

2) In the TUB, Serrasalmus species bit 100% the weaker and smaller of their own kind. Once the smaller was devoid of fins, it became a target for the larger Pygocentrus species. Three (3) S. sanchezi were lost in this TUB TEST in the beginning by fin bites by the two largest S. sanchezi. Once the fishes was disabled, it became prey to Pygocentrus.

3) Pygocentrus species, primarily stay within their group, with a few smaller members staying among the rocks and roots. There was little aggressive behavior among them, other than some posturing for position, tail slapping, and nudging. They did on occasion chase the S. sanchezi away. As of this date, they still are staying within their respective groups. The remaining S. sanchezi continues to stalk them. Only a few attempts by Pygocentrus to bite this lone remaining S. sanchezi have occurred. 

4) Serrasalmus species, primarily stayed alone and did not group. They drove away and bit any other species coming near them. Mostly chasing after the smaller Serrasalmus in attempts to bite the tail fin. The last small S. sanchezi was bit on all fins prior to meeting its demise. At the time of mortality this smaller species was approximately 5  inches TL. The larger S. sanchezi was about 1/2 inch larger. While this larger fish remains in the TUB, it has only a bit dorsal fin that appears to be the exact jaw size of the smaller S. sanchezi that died. No other parts of this fish appears bit. 

In conclusion, it remains my opinion, that regardless of what sized aquarium is used, the Serrasalmus species will naturally stalk, using stealth, to bite the fins of other species. Once the prey fish is disabled, it becomes food for any other species. The water temperature had little to do with the outcome. At the time of mortality, water temperature was 72F, well below the norm for these species. The entire species were well-fed on cut fish (catfish and Tilapia). They also received daily feedings of large jumbo shrimp. None of this prevented the outcome.  While there remains one S. sanchezi alive, this fish will be allowed to remain in the TUB. Attempts to capture it have failed as it swims quickly for cover in the rocks and roots. In order to remove it would require taking out all these things and then the entire TUB will be stressed, probably causing additional bites or worse mortality.  My final act on this page will be to post the end results of this last fish. So long as the fish avoids being trapped and cornered by Pygocentrus group, it should remain alive for an unknown period of time. Readers are reminded that Pygocentrus uses pack techniques. This technique allows one member to chase the prey fish into a corner or area where it cannot escape. It is at this point the pack will attack and eat the prey. This behavior is seen among mammals, namely wolves. Also, should Pygocentrus severely bite the tail region of S. sanchezi, it likely would be only moments before the entire group attacks the fish and eat it. I have seen over the years, this very same behavior. So hobbyists who wish to attempt this type of aquarium setup, should be aware that long term goals are not in the forecast for success with these species. While the fish may survive for a number of months, perhaps a couple years or so, in the end, the species will not deter and will practice its natural behavior in the aquarium. 

• July 9, 2005. The remaining S. sanchezi was eaten. Several other Pygocentrus have been eaten as well, 

• August 24, 2005. 1 ternetzi met its demise, while one other smaller one was bitten on the side so bad, that I removed it. 

• September 5, 2005. I returned the damaged ternetzi back to the tub. The fish had completely healed from its deep flank bites. Amazing how these fish regenerate flesh from near mortal wounds.

Readers may also read a separate article on S. sanchezi being kept as a pair in a species only aquarium. Simply click this link. Frank Magallanes, OPEFE - September 9, 2005 

REFERENCES

• L.N. Carvalho, K. Del-Claro, and R. M. Takemoto, Host-Parasite interaction between branchiurans (Crustacea: Argulidae), Environmental Biology of Fishes. 67: 289-296, 2003.

• Sazima, I. and F. A. Machado. 1990. Underwater observations of piranhas in Western Brazil, Env. Biol. Fish. 28: 17-31.

• Schleser, David M. 1997 Piranhas A complete Pet Owner's Manual, Baron's Educational Series, Inc. pg. 58-59.

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