Principles of Genetics and Breeding

15.1.3.Fish seed quality assurance

Poor quality seed, perceived as a major constraint to expansion of fish culture, can have deleterious effect on fish production and broodstock development. Some countries have adopted several approaches to ensure fish seed quality.

China has established an institutional approach to ensure fish seed quality. As per “Aquatic Seed Management” definition of the Ministry of Agriculture, fish breeders should obtain the broodstock from one of the centres established under the National Aquatic Bred and Wild Seed System (NABWSS), which includes Genetic Breeding Center (GBC), Wild Variety Collection Center (WVCC), Wild/Bred Variety Amplifier (WBVA), Exotic Species Centers (ESC) and Seed Quality Inspection Centers (SQIC).

A certification process has also been adopted but limited to the authorization of the release of genetically improved varieties. Under this certification process the National Certification Committee of Aquatic Wild and Bred Varieties (NCCA-WBV) has authorized the release of 32 strains, including 16 selective and 16 crossbreeding strains. Success of such public institutional approach suffers from inability to meet the demand for broodstock and more emphasis on licensing than quality assessment.

Criteria and standards are available to assess seed and broodstock quality.

Quality criteria are largely based on age and uniformity of size in terms of weight and length (Indonesia, Thailand), growth performance, survival and percentage of deformities (Vietnam) and body shape and behaviour (Sri Lanka).

Some farmers have experienced sudden spawn deaths and occurrence of deformed larvae/fry, more common for spawn produced during late breeding season, thus, farmers tend to avoid breeding during late spawning season.

Further investigations are required to select and establish better criteria for quality assurance. In Bangladesh and Indonesia, fish seed quality criteria have been adopted as national standards for eight species (common carp, Nile tilapia, Siamese catfish, walking catfish, gouramy, giant freshwater prawn and bullfrog).

Quality of fish seed for sex reversed tilapia (SRT) and genetically male tilapia (GMT) are often assessed by the occurrence of any breeding in the production stock from unwanted females. Fish seed quality assurance through health management is widely used as disease is considered as one of the important problematic factors in the seed industry. Parasitic diseases in nursery is one of the most important limiting factors for growth and survival of fry and fingerling.

In many Asian countries, severe mortalities among carp fry have been reported and it was caused by different parasites such as Ichthyopthirius sp. (ich disease), Trichodina spp., Ichthyobodo spp., Lernaea spp., Myxobolus spp. and Dactylogyrus spp. Myxobolus and Henneguya affect the gills and have caused heavy mortalities in Catla catla.

The most commonly adopted approach is periodic checks on the health status of fish seed and carrying out recommended treatment (Sri Lanka, Thailand, Bangladesh, India). During an outbreak of a disease in hatcheries and nurseries, farmers used different treatments such as chemicals and antibiotics, water exchange and manipulation of feeding and fertilization. Prophylactic treatment is a common practice.

Health management practices are often considered as part of good husbandry (Sri Lanka, Pakistan). There are no specific/unique procedures or standards developed for maintaining hygienic condition in fish hatcheries but most hatcheries take precautionary measures before and during fry production. As a part of the precaution, disinfection of facilities and materials in use is commonly practiced.

A communal or mixed spawning system for major carps in West Bengal is being practiced and is known to produce approximately 10 percent hybrids. This technique may lead to loss of genetic purity of important major carps. Fish farmers often complain about poor growth of fish procured from certain hatcheries, particularly small-scale or farmer-operated hatcheries. They feel that such fish do not reach marketable size within the stipulated period. This is also attributed to inbreeding.

Small-scale hatchery operations, particularly farmer operated hatcheries, can rapidly give rise to deterioration of broodstock quality due to their limited capacity to maintain minimum effective population size of broodstock. Small-scale farmer hatcheries usually maintain multi-species broodstock in one or two ponds with excessive stocking densities. The broodstock ponds usually were either underfed or fed with low quality feed. Competition between fish species may also limit the potential of each stocked fish species in terms of maturation, fecundity, fertilization, hatching success and survival rates.

It is reported that these hatcheries rarely recruit new broods from outside. If they do, the recruitment is from the subsequent generations of the same parent stock without any inflowing of new genetic material. In many hatcheries, the common practice of using the same brooders more than once in a breeding season causes deterioration of larval quality, mortality and larval deformity.

Hatcheries are more concerned with quantity rather than the quality of fish seed; production does not follow any selection procedure, thus, high mortality rates, poor growth and high susceptibility to disease and other parasitic infection are common occurrence. Several initiatives have been taken to preserve the genetic quality of broodstock to assure high quality seed.