Objectives

The objective of the study is to investigate genetic issues relevant to the aquaculture, stock enhancement and fisheries management of rohu. The project aims to improve broodstock management practices at the hatchery level, support fisheries management and inform policy development on the translocation of seed for aquaculture and/or stock enhancement. These objectives will be addressed through five inter-linked molecular genetic studies.

Background and significance

The rohu, Labeo rohita, is an herbivorous cyprinid fish that inhabits the tropical lowland river systems of Pakistan, northern India, Nepal, Bangladesh and Myanmar. Rohu is considered to be the most important of the Indian 'major carps' and is the world's 10th highest cultured finfish by production volume. Approximately 1.2 million tonnes were produced in 2005 valued at more than US$1.6 billion. The major producing countries are India, Bangladesh and Myanmar. Rohu is also a substantial component of stock enhancement programs in floodplains and open waters in these countries, and it has been widely translocated both within and external to its natural range.

Issues

As with many other aquaculture commodities in the Asian region, rohu aquaculture is facing issues pertaining to seed quality including poor genetic management of broodstock. Awareness of genetic issues in the region is low. Hatcheries commonly maintain minimal broodstock populations, recruit successive generations of broodstock from within the ‘system’ and spawn multiple species simultaneously in common tanks to minimise production costs. The available evidence supports a widely-held perception that genetic degradation of hatchery stocks is occurring, and that both inbreeding depression and inadvertent hybridisation are common problems contributing to poor quality seed production.

With inbreeding, hybridisation and translocation widespread, concerns have also been raised over the potential impact of hatchery-produced rohu seed on the genetic integrity of wild rohu populations. However, the extent of genetic differentiation among rohu populations is largely unknown and so the significance of this issue cannot presently be assessed. The available data on rohu population structure consists of two limited studies confined to Bangladesh and anecdotal reports from India. There is presently no data on population structure over a larger spatial scale or between the major river basins.

The taxonomy of the genus Labeo has been the subject of some confusion. Approximately 105 extant species are recognised which confined to Africa and Asia (Fishbase 2008). While African Labeo species were revised by Reid (1985) and Indian species were revised by Jayaram and Dhas (2000), both revisions were made on the basis of morphological characteristics. To date the phylogeny of the group has escaped molecular genetic analysis and the genetic relationships between rohu and other species of Labeo remain unknown.

Expected outputs

The aim of "Project rohu" is to:

• Assess the genetic structure of rohu populations across its vast natural range.
• Investigate the phylogeography of rohu populations.
• Assess broodstock management practices and genetic diversity in selected hatchery populations used for aquaculture and stock enhancement.
• Develop a broodstock management plan for one or more public hatcheries to maintain genetic diversity and minimise the potential impacts of hatchery-produced seed on the genetic integrity of wild populations.
• Investigate the phylogenetic relationships between Asian Labeo species.

These objectives will be addressed through five inter-linked studies utilising nuclear DNA microsatellite markers, restriction fragment length polymorphisms (RFLPs), and direct sequencing of mitochondrial DNA gene regions.

Progress

• A field mission to Myanmar was conducted in May 2007 to assess broodstock management practices and collect wild samples from the Ayeyarwaddy Delta and adjacent hatcheries. Additional samples from the central and northern Ayeyarwaddy were gathered by the Myanmar DOF in the latter half of the year.
• A field mission to Bangladesh was conducted in November 2008 to collect samples of wild rohu from the Padma, Jamuna and Halda Rivers, as well as samples from commercial hatcheries and of an improved rohu strain in development, with the assistance of the Bangladesh Fisheries Research Institute (BFRI) stations in Jessore and Mymensingh, and the Bangladesh Agricultural University.

How you can help

There are several ways to get involved in the project:

Population genetics of rohu: We need to collect samples of wild rohu from across their vast natural range. Please contact us if you can help collect finclips from live fish in your area (check the map below to see the natural distribution of rohu as it is actually an alien species in many areas).

Broodstock management practices: We are looking for hatchery partners wish to improve their seed quality. We would like to hear from hatcheries that have inbreeding or hybridisation issues and are willing to participate in research to identify better broodstock management practices.

Phylogenetics of Labeo spp.: We need samples of as many Labeo species as possible in order to conduct the phylogenetic study. Please contact us if you are able to help collect finclips from live Labeo species in your area.

NACA will cover costs and supply necessary equipment for collection of samples. All contributions will be acknowledged in the outputs of the study.

• Map of rohu distribution (click to open).
• Instructions on how to collect and preserve finclip samples for genetic analysis.

Contacts

For more information about 'Project Rohu', contact:

Simon Wilkinson
Communications Manager
Network of Aquaculture Centres in Asia-Pacific
Phone: +66 2 561 1728
Fax: +66 2 561 1727