Welcome Gokul!
Given the number of goldfish you have (now at over a year in age) and the tank capacity they're kept in leads me to believe the initial symptoms they displayed have lead to a more advanced bacterial infection.. fin rot, septicemia.
To avoid this chain of events from getting started and progressing this way, we recommend 15 gallons of water per goldfish (fancies like orandas and moors) and 20 gallons of water per goldfish (for pond types like commons and comets) -- as a minimum based on their adult size. In addition to tank size, we also recommend at least double if not quadruple the usual level of filtration a tropical tank of equal size would need. This combination of large tank volume/size plus heavier filtration lets us maintain their environment equally with normal maintenance (filter cleaning, weekly water changes, and so on) as we would do with any other standard tropical community fish tank.
As goldfish start out so small when they are purchased, that often seems like an excessively large rule of thumb to follow for most people. "Really? I need a tank that big for just a few small fish??" And the answer to that question is... "Yes, you do". This really is what they need for healthy long-term care.
Because goldfish grow so fast to get this large within the first year of age, they effectively outgrow the tank they are in. And what originally seemed adequate for their health and well being all those preceding months is no longer the case. As in the comment you've made here:
They are housed in this tank for last one year without any trouble.
Using the 15-gallon estimate for the 3 orandas + 2 moors you have would give us a minimum tank size requirement of at least 75 gallons (minimum) to keep everyone healthy. It may not seem this way to you, but the 65 gallon tank has become overstocked and overcrowded for the 5 goldfish you have. Even with excellent water quality (which it may or may not be anymore), these conditions lead to high stress and a weakened immune system.. and this makes them susceptible to bacterial infection, parasites, and other common diseases.
Red lines, streaks, or blotches in the tail and finnage is an early warning sign that highly stressful conditions exist -- and fish that are prone to serious health problems if these conditions are not corrected right away. The fins maybe begin to also split, fray, or degrade. Even with medication this condition can spread further because the underlying cause of the problem (overcrowding, tank too small, inadequate filtration, poor water quality) has not changed. In reality, we are only treating the symptoms -- not the cause. And the originating problem that started this has not been corrected.
I see red/darkred lines/inflammation under the jaw and under belly.Esp along the joins and fins. I am treating them with Tetracycline tablets with flakes every day.
After feeding flakes with tetracycline they seems to be active,but red lines doesnt seem to go.
I would surmise that the stress/conditions lead to a bacterial infection. (What begins visibly with the finnage will enter the body itself as the infection spreads. Septicemia is infection through the bloodstream). The inflammation/etc. that you saw under the jaw and belly shows the infection went that far before your treatment started.
You began treatment using tetracycline, which has helped enormously and may have saved the lives of your fish at this more advanced stage because it's keeping the current infection in check. But this is only a temporary measure that has slowed the process for the present time. The red lines aren't going away because the root cause of these problems (tank size/etc.) remains the same. You should continue your current treatment to keep the infection from spreading... and do whatever you can to place these fish in larger quarters as fast as possible.
If you can set up quarantine tanks for 1 or 2 of the fish either together or separately... then leave 3 of them in the 65 gallon where they are now. Keeping all 5 of them together in this tank isn't going to work anymore. If you can't manage a very fast upgrade or provide large QT places for some of them, you might have to choose between them at this point to avoid losing them all.
I suspect it could be either Flukes/Internal Parasite or Red Pest!! Am I correct?
Can I treat them with Acriflavine? Whats the dosage?
Please advice
It's hard to tell what other problems may also be present. What you've described to us already is enough to explain the known problems and why your treatment so far has showed some very positive signs of improvement. So far, so good! Given the situation, you've done a great job with this.
As a word of caution, though... it's very easy for us to go looking for new diseases/parasites that aren't even there to explain lingering problems (symptoms) that hang on because basic conditions they're in haven't improved. We're also much too quick to medicate for problems that don't exist, which isn't going to help at all. Adding more meds and treatment for parasites isn't the answer. If you can solve the overstocked tank issue and provide high quality water conditions for them, your fish will then be able to fully recover from this with no other (new) forms of treatment necessary. At that point, yes.. I would also watch for signs of parasites or anything else that seems unusual.
Your goldfish are on their way to better health. Good luck with this... keep asking questions you might have... and let us know how well things go.
