It depends on the species.
Sometimes it can be cannibalism (if the fish are predatory, and the difference in body size is large among individuals) or it can be aggression among individuals.
The main cause of different parasite invasions or fish diseases is overcrowding in relatively small cage area. This is basic background to increase of stress of cultured fish giving "open door" to lowering immunological protection. So in different types of cage cultures it seems to be one of more important factors to recognize.
If over crowding intra-species competition for food and space can caused to stress condition and ultimately weak the fishes report mortality. Deterioration of water quality due to nutrients loading, increase the algal bio mass may also effected to mass mortality among cultured fish.
I do agree that (all kinds of) pathogens are the main cause of mortality in net cages. To be honest farmed fish are under a constant stress that could be nutritional, environmental or behavioural. Organisms under stress do show a significant decrease in their immune status and that very fact makes the occurance of mortality much easier. As mentioned, environmental parameters (I could mention oxygen as the major one) are also contributing in resulting mortalities, especially if the nets are not allowing a free water flow.
Lack of oxygen as mentioned above would be caused by nets not being cleaned regularly and completely covered by fouling organisms.
Hi, it depends on what kind of net as well as fish kind and also the location. Several possible reasons could be
-DO, the oxygen
-pollution
-tide and current
-feed
-weather or temperature changes
-red tide
-or disease and virus
Etc.
An acceptable Mortality Rate ranges from 8% to 12%, however if you are experiencing a higher MR check your system MCC (Maximum Carrying Capacity) which is related to the body of water where the cages are located, as well as the fish specie being raised.
in the confined net-cage environment, mortality is often seen. Signs include abnormalities in behaviour, darkened body, exophthalmia (pop eye) and ulcerations on the fish body. There are many causes of fish mortality in the confined net-cage environment but possible causes for these disease outbreaks are pathogenic parasites. - See more at: http://www.thefishsite.com/articles/177/important-parasitic-diseases-in-cultured-marine-fish-in-the-asiapacific-region#sthash.KcSbzphr.dpuf
Dear Mohammad, the main cause of death in marine aquarium is parasitic (Oodinium and Cryptocarion irritans, as dinoflagelates and protozoa, respectively; and monogenea trematoda). Brazilian Hugs
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