INTRODUCTION

I have been keeping these fish solo and in groups for over 3 years and consist of 13 different S. geryi. My first experiences with grouping them in a single tank ended quickly because of the heightened aggression of one of the larger specimens I obtained. After a few different attempts piecing a tank together with geryi from many different hobbyists, I was able to get 5 geryi 3"-4” that had been recently imported. These fish lived together for 2 years, growing to 6”-7”. 

I had very little fighting with this group and only one time had to remove a fish for an injury to its eye which fully healed in a week. Unfortunately, 2 of these fish died in the transition from Wisconsin to Oregon. I have since acquired 4 more ranging from 7” to 10”. So my current group consists of 7 S. geryi ranging from 7” to 10” in a 180 gallon tank. This group has been together about 4 months. The tank has a sand substrate with some driftwood and live/fake plants. Contrary to popular belief, my experience with this fish is that in a comfortable situation the fish will not remain on the bottom half of the tank but prefers to dwell in the middle to upper-middle portion of the tank. When the group is startled by an outside disturbance they will huddle as a group in a bottom corner but under normal circumstances they are much more apt to stay at the top half of the tank. They are not a skittish fish when compared to Pygocentrus or other Serrasalmus species I have kept.

My current group were initially housed in a 125 gallon tank. They acted very territorial and they did not eat for almost 2 weeks after introduction. In the past I would have used feeders to stem any aggression but I choose not to use any with this group. The result of the 2 weeks fasting period was minor fin nipping and one or 2 minor body bites. They would eat very sparingly in while in the 125 which in my experience is quite unusual. They would remain for long periods on the bottom of the tank and almost never swim around and were very skittish with movement outside the tank.

When I moved them to a 180 gallon tank, the dynamic changed completely…and basically over night. Now they eat amazingly well and they are in continual movement, almost never remaining in one spot for very long and almost always dwell around the upper half of the tank. They are much more curious about what is going on outside of the tank. When I enter the fish room they will all move to the front of the tank. During tank cleaning they will not hide or move away from the siphon but prefer to remain in their areas and be gently nudged out of the way for cleaning.

DETAILED OBSERVATIONS

Feeding

They readily accept non-live foods when provided.

Aggression

These fish do not shoal and aggression is based on territory and not on hunger. They set up territories that consist of an area from the substrate to the top of the tank and will chase others away when that territory is entered. I am yet to experience any aggression when changing feeding schedule from daily to weekly. Smaller fish are kept in check and are not allowed to establish a territory that will in anyway be construed as the premier spots in the tank. They take the brunt of almost all aggression and in my tank they understand their roll by staying out of any established area of the more dominant fish.

Light

My experience with S. geryi has led me to believe they not only accept a lighted tank but will actually seek out the more well let portions of the tank. When only one half of my tank was lit, they would spend their time under the well lit areas as apposed to the non-lit areas.

Suggested tank

In my tank these fish utilize a higher water column than any other species of piranha I have kept. I would suggest a taller tank to any hobbyist interested in keeping these fish. They do not stay on the bottom of the tank and seem to prefer the upper half of the tank.

Body Shape

A true member of the compresses group and the difference between a 7" fish and a 9" fish is shocking. The height of these fish increases much more than the length as they grow.

UPDATED: 07/09/2009