Aquatic ecology and Biodiversity

Unit 12- Biodiversity and conservation

12.3.10. Fish passes to migratory fishes
Fish populations are highly dependent upon the characteristics of their aquatic habitat which supports all their biological functions. Migratory fish require different environments for the main phases of their life cycle such as reproduction, production of juveniles, growth and sexual maturation.

The objective of fish pass is to move the whole migrating population through. The efficiency of a fish pass is expressed both in terms of the percentage of the population which clear the obstacle and the migration delay. Whatever the case, the fish pass must be sufficiently efficient so as not to constitute a limiting factor in the long-term maintenance of migrating stock.
The dam prevents migration between feeding and breeding zones. The effect can become severe, leading to the extinction of species and loss of biodiversity, where no spawning grounds are present in the river or its tributary downstream of the dam. The reduction of biodiversity occurred not only in the flooded section but also in the river below the dam.
On the Indus river, the construction of the Gulam Mahommed Dam has deprived the migratory Hillsa ilisha of 60% of their previous spawning areas (Welcomme, 1985). To conserve fish biodiversity fish passes are essential.