Conservation programmes help fish production to be more sustainable while at the same time maintaining diversity. Conserving diversity also improves the likelihood of maintaining minimal viable populations of rare and late-successional species. Maintaining ichthyo diversity is important because it is not always possible to identify which individual species are critical to aquatic ecosystem's sustainability. Many fish species may provide genetic material and may serve as ecological indicators. Diversity reduces disease problems and encourages recovery from disturbance. Although, over the past billion years, adaptation and diversification has tended to increase the number of species, with the escalation of human population, their infringing into the wilderness and rapid industrialisation, a decline in species diversity became noticeable. This decline is sometimes associated with the destruction of aquatic ecosystems. The situation is rather in an aggravated condition in the Lakes like Sone ecosystem situated in the tropical developing countries where the process of species extinction and genetic loss may become severe in future due to loss of habitat by siltation, blockade of the waterways, injudicious introduction of exotic fish species, irrational harvest of the juveniles and fish diseases (Kar, et.al. 1995b).

Fish conservation in Sone may be practiced either in situ or ex situ. Methods such as secluding portions of the Lake as 'aquareserves' with minimum viable population size in it could be practiced as in situ conservation strategy in the lake Sone. Ex situ conservation may involve preservation of the gene pool as an insurance against loss in in situ reserves. In situ is best achieved both in natural and man-made ecosystems. The concept mainly revolves around the conservation of endemic species. This method has the advantage of being less expensive than ex situ measures in the long run and also allows continued co-evolution with other species. Ex situ approach takes care of species outside their natural habitats, especially in farms or genetic resource conservation centres. The ultimate ex-situ measures are the gene banks where cryostorage of gametes and embryos are achieved.

A number of stresses, mostly man made, have been operating on fishes, to the grave detriment of these species in their once ideal environments. The obvious fallout of these on commercial species is through reduced catch per unit effort. Unlike commercial species, where depletion or decline of numbers is easily detectable, and some remedial measures taken, uneconomical species, though a part of the biodiversity, may not even get noticed even if affected.

Reclamation of water bodies for construction of buildings and agricultural purposes destroys the natural habitat of fishes. Due to the increasing human population pressure, many of the natural water bodies have either reduced in size or completely disappeared. Removal of bottom sand and gravel from river beds has been another menace destructing the natural spawning grounds of fishes. Bottom feeders are also affected as the bottom flora and fauna get removed alongwith the gravel collections.

Over-exploitation had been having tremendous bad impact on fish diversity. Notopterus chitala and Semiplotus semiplotus, which used to be abundant in the large rivers of Assam and attaining large sizes, are becoming rarer now due to over exploitation. Unconventional and illegal fishing methods, like use of banned nets, electric fishing, use of explosives, etc. cause mass mortality, and kill the unwanted fishes in addition to the commercial species. Many of the smaller fishes are also killed using these methods. In the case of mahseer, the main causes of depletion are wanton destruction of brood fish and juveniles and the deteriorating ecological conditions of the spawning and rearing grounds. Large sized mahseers are more convenient targets. Discarded food articles are used as bait and dynamite is thrown when large and small fish congregate. This results in wholesale slaughter of the entire population.

Introduction of exotic species as a part of aquaculture for commercial gains has resulted in loss of diversity. For e.g. the Schizothoracine fishes in Kashmir valley have almost been exterminated by the exotic common carp Cyprinus carpio species. The Loktak fish of Manipur is fast disappearing, once again, due to the introduction of common carp for culture. The displacement of Catla species from many reservoirs and its associated ecological disaster is noticed after introduction of silver carp as in Govindsagar and some other reservoirs. The consequences of pollution in water bodies due to industrial and domestic pollutants are far reaching. The obvious outcome of pollution is stress and death of individuals. In cases of genotoxic pollutants, the effect can be more damaging but subtle. A number of fishes have been displaced or eliminated from their original habitats. Among the range of various diseases caused by bacteria, fungi, virus, etc. the most virulent and menacing one threatening many species is the Epizootic Ulcerative Syndrome (EUS). It has wiped out large population of a number of commercial and non-commercial species in Asian region resulting in severe erosion of genetic variability and biodiversity.

Though a number of causes have been identified, it has been not possible to totally undo the damage caused by each factor. A holistic approach integrating the concept of sustainable development and conservation measures can help. Control measures such as . diversion of effluent (for treatment) in some lakes have shown appreciable improvement in the levels of a number of ecological parameters like dissolved oxygen, free carbon dioxide total alkalinity etc. Fish production potentials improved from 5-39% in just one year.