It is possible for your fish not to have any disease. However, this is only possible if you take every precaution at preventing diseases which include adequate and proper feeding, good water maintenance and prevention of stressful conditions.
All these are based on the assumption that your fishes either fingerlings or juveniles are gotten from a very good source where possible diseases from the hatchery have been eliminated. So it is possible for your fish not to be sick at all but adequate attention must be given to them in order to ensure that.
How to know when your fishes are sick
Like any other animal, it is not difficult to know when fish are sick. The signs you will observe include the following: loss of interest in feeds and feeding, the fish will begin to loose weight, some may rub their body against the wall of the pond which will result to their skin peeling off, and some of the fish may show erratic movement in the pond and may attempt jumping out of the pond.
There could be sudden change in the body coloration of the fish. The last stage is high mortality in the pond. All these are signs that should make a farmer suspect disease on his farm.
Possible things that can introduce disease to your fishes
Things that can introduce diseases to your fish are many which include: their feed, water and the way they are handled by the attendants. Generally, disease-causing organisms (virus, bacteria, fungi etc) ate the ones that will cause the disease.
Feeds, water and other means will just act as the carrier of these organisms. So always watch the feed, water and the way your attendants handle the fish and the pond so that diseases are not introduced to your farm.
To know whether the disease affecting your fish is from hatchery or from your farm, so many things must be considered. At first be sure that your pond and the source of your water is very good and you then experience mortality in the first one week of life, you may suspect hatchery problem. This is after you have eliminated stress due to transportation or stocking.
Now, if mortality starts occurring after a week of life, I will advice that you critically observe all the activities on your farm for it is likely that the problem is from your farm. It may be due to stress, the kind of feed you are giving them, the water in the pond etc.
As for the symptoms of the fish, they can begin to show signs of ill-health as from any stage even as from Day Old so before venturing into fish farming, it is advisable that you have enough knowledge of the diseases that can affect them including the age at which they could be affected and what you will do if the problems occur. Always consult an expert for details on this.