UNKNOWN KILLER

Question
I HAVE KEPT VARIOUS SIZE TANKS FOR YEARS AND HAVE NEVER HAD THIS PROBLEM.  I CURRENTLY HAVE A 75 GALLON FRESHWATER TANK.  I HAVE SEVERAL TYPES OF TETRAS, 2 ANGELS, SEVERAL CATFISH, 3 RASBORA, 1 ZEBRA DANIO, 3 SMALL TYPE ALGEA EATERS (THEY DO NOT GROW LIKE THE OTHER ALGEA EATERS) 4 SNAILS, 3 BAMBOO SHRIMP, 2 LARGE ALGEA EATERS, 1 MEDIUM/LARGE PLECTMOUS (?) AND 2 MEDIUM/LARGE UNKNOWN CATFISH SPECIES. I BOUGHT THE UNKNOWN CATFISH THINKING THEY WERE LIKE MY OTHER CATS.  BEFORE I KNEW IT THEY BECAME QUITE LARGE.  I HAVE HAD THESE LARGE FISH FOR OVER A YEAR WITH NO PROBLEMS.  WITHIN THE LAST 2 WEEKS I HAVE LOST ROUGHLY 12 NEONS.  IT APPEARS AS THOUGH SOMEONE IS KILLING THEM.  THEY EITHER HAVE A CHUNK FROM THEIR UNDERBELLY OR THEY ARE MISSING THE TAIL END.  IT IS STRANGE THAT THE NEONS WERE THE ONLY ONES BEING ATTACKED.  TODAY HOWEVER I NOTICED I AM MISSING A DANIO AND FOUND THE BODY OF ONE OF THE SMALL ALGEA TYPE SPECIES. I AM THINKING IT MAY BE THE ALGEA EATERS.  I HAVE HEARD THEY GET AGGRESSIVE AS THEY AGE.  I ALSO ADDED SOME COLORED LIGHTING THAT I RUN AT NIGHT.  THE 3 LARGE FISH I HAVE ARE FULLY CAPABLE OF EATING THE TETRAS WHOLE AND HAVE NEVER EATEN ANYONE THAT I KNOW OF SO I DO NOT THINK IT IS THEM.  THEY LIKE TO STAY HIDDEN FOR THE MOST PART.  ANY HELP YOU CAN GIVE WILL BE APPRECIATED. SORRY I DO NOT KNOW THE EXACT NAMES OF THOSE SMALL ALGEA GUYS BUT THEY ARE VERY PETITE.

Answer
Dear Jo,
I wonder if the culprit to all the horrible fish loss is the Angelfish. Although they are usually compatable with most fish, they can be predators if they decide to, or the fish are small enough. Neons are typically the perfect size for Angelfish to try to attack and it is well known that Angels will almost always disturb neons at one point or another. Don't get me wrong, I cherish Angelfish, but they can be predators in the aquarium and that is something you should look out for. I currently keep my Angelfish with zebra danios and other community small community fish such as guppies and barbs, but they don't seem to disturb them much at all. But of course not to say they never -will- disturb the smaller creatures.

The mystery Algae eaters are another possible culprit. Chinese Algae eaters are the most commonly available of the algae eaters next to the Plecostomus, however, unlike the plecostomus, the Chinese Algae eater has been known to attack fish and cause fish loss as well as it grows large.  Known to chase and harass other fish they may also use their sucking mouth to rasp on the sides of the fish if they can. Chinese algae eaters can reach 8 inches at full size. If you are unsure as to the species of your 2 Large algae eaters, here are some links to photos of the Chinese algae eaters-
http://www.petresources.net/fish/cyprinid/gyr_aym.html
http://www.aquahobby.com/gallery/e_Gyrinocheilus_aymonieri.php

Sounds to me like the small petite algae eaters you are speaking of surely sound like the tiny Otocinclus catfish, sometimes commonly called "O-cats" or simply just "Ottos" these are entirely peaceful algae eaters that do an excellent job at cleaning algae and never grow larger than 2 inches at max. Here are some links to help-
http://www.aquariumadvice.com/profiles/6_12_en.html
http://aquaticgardens.blogspot.com/2006/07/otocinclus-catfish.html

You will have to do some good observations in your aquarium and remember that a lot of fish hunting and attacks happens at night when nobody is around to see.
I hope the above suggestions help you out in the finding the real cuplrit of the sad fish loss you've been encountering.

Feel free to write again if you need anymore help!
Best wishes,
Karen~