06-05-2009, 10:00 AM
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Sexing corys isn't easy, and I have had them spawn. The females are rounder when mature. Watch their behaviour, and if you think they are in spawning mode, do a partial water change (40-50%) using water a tad cooler (stimulates a tropical rainstorm which is when they spawn in nature) and do the pwc on a day when there is a low pressure system outside. Fish can sense this (characins regularly spawn when bad weather moves in!), and again it stimulates them as it does in the wild. If you have male and female, they may spawn under this scenario if they are at all ready and mature.
Re the diatoms, no, corys will not eat algae. They will graze through brush algae looking for bits of food. They do not eat any algae.
They do often like to swim into the fresh water entering the tank during a pwc. I wouldn't take this as a sign of anything actually problematical with the existing tank water, though obviously it could be. Corys are sensitive to water quality and parameters, and they do not like significant changes nor do they like to be moved to another tank.
IonBaller007, was there a name on these corys at the store? Might give a clue as to what they are, as different species can behave differently or encounter different problems. How long have you had them, and are they still behaving as you described previously? What is your pH and hardness, and temperature (some corys cannot tolerate higher temps)?
Fishin Pole, lucky you...I think C. duplicareus is one of the nicest looking corys; I currently have one which is all I have so far found in the local stores. I had a group of them back in 1995 shortly after they were scientifically described and named (July 1995 FAMA) by Dr. David Sands who discovered them in 1992 in a northern tributary of the Rio Negro. A near-identical species was also discovered at the same time in the same river, and named C. serratus by Sands due to the serrated pectoral spine (C. duplicareus has a smooth pectoral spine). Of all the similar-looking species (C. adolfoi and its mimic C. imitator, C. duplicareus and mimic C. serratus), C. duplicareus has the brightest orange post-orbital fleck and the broad black dorsallateral band. A very impressive and attractive little fish.