So my friend sent me a text and said his new fish died. He bought a baby GT and A baby jag. They were in a 10 gallon tank i gave him. He used a old filter i gave him with a used filter cartridge and i gave him some gravel. The tank rain for 4 days with no fish. He said the 2 fish were chasing each other all day and night but both were fine this morn. He got home and the jag was dead wiht its mouth ope. He wanted to know what this meant and how it was caused. He also said he tested the tank and found nothing wrong with the water parameters. Is this lockjaw or something else as ive never seen it b4? i said the GT probly stressed the jag to death.