Though I am not expert in this field, my general observation is that there is lack of proper investment in the countries in this area. So, without proper investment, research and policy priority sustainability is in question. 

Rural aquaculture actually practiced in the Asia-Pacific region at sustainable basis but its successful implementation faced myriads of social, cultural, financial and technological difficulties. However, it contributes to about 40% of the total fish supply.

It depends. Literature suggests that the higher intensity is the greater are dangers of environmental degradation such as pollution of groundwater and unwanted social consequences. High intensity also often leads to replacement of local producer and graping of land by industrial aquaculture enterprises. South-east India, Thailand (and other countries in South-east Asia) have mixed experience. Problems with viral diseases lead to use of dangerous antibiotics which can pollute groundwater. Some critical studies have been published in the 1990s in the Frontline Magazine published by The Hindu. From this time there are also court decsions which place people's livelihoods higher than private profits (e.g. with regards to plans by TATA company to start shrimp aquaculture at Chilika Lake in Orissa). Some information should be available from FIAN, a Human Rights organization as well as from the Centre of Science and Envrionment (CSE, New Delhi). If required I could copy / scan some articles and send them.