No field of agriculture offers such potential for continuous long term crop improvement as genetics. Over the last 40 years, the growth rate of broilers has increased over 400%, and studies have shown that 78% of this gain is due to genetic selection. Studies with shrimp have indicated potential gains of 5-15% per year.
Although a spectrum of shrimp breeding programs have been attempted, the most successful model is that of the US Marine Shrimp Farming Consortium. This is based on a foundation population of specific pathogen free (SPF) Pacific white shrimp (Litopenaeus vannamei) which are subjected to long term family-level selection. This approach has led to a healthy, fast growing population of Pacific white shrimp which have displaced much of the native shrimp in China, Thailand, Indonesia, and Vietnam.
Much opportunity exists for further genetic improvement of Pacific white shrimp-- specifically for selection of traits that perform well in specific local environments. In addition, similar breeding programs can be developed for other promising species such as black tiger shrimp (Penaeus monodon), blue shrimp (Litopenaeus stylirostris), Chinese white shrimp (Fenneropenaeus chinensis), Indian white shrimp (Fenneropenaeus indicus), Japanese tiger shrimp (Marsupenaeus japonicas).
IAI is committed to the proven integrated approach involving healthy breeding stocks, quality feeds, and strict production management. Such a program requires an experienced interdisciplinary team of experts to avoid costly and time consuming errors and oversights. The following is a brief description of the principle features of an IA Genetics program.
To avoid the confounding effects of disease, the breeding program should begin with SPF breeding populations (see IA Health) housed within a Nucleus Breeding Center (NBC). The NBC is a biosecure facility isolated from shrimp farming activity. The facility is enclosed to avoid contamination by birds and insects, and the buildings and water treatment systems are designed to facilitate proper sanitation and disinfection. Staff are well trained in biosecurity techniques, and continual disease surveillance assures the SPF status of stocks.
NBC Implementation
- Rearing of breeding stock to reproductive size
- Inducing maturation in captivity
- Mating through natural or artificial insemination. Artificial insemination allows production of half sib families
- Isolation of each spawn as an individual family
- Larval rearing of each family to advanced postlarvae
- Rearing of postlarvae to 3-4 g
- Tagging of individuals within each family with a unique combination of elastomer dyes
- Pooling a portion of each tagged family in a common environment within the NBC and rearing to market size
- Exporting the remainder of tagged families for field trials and laboratory disease challenge
- Comparison of performance of families within the NBC, field trials, and laboratory challenge trials
- Selection of families with preferred traits
- Grow-out of preferred families to reproductive size
A variety of criteria can be used to select families. The typical approach is to begin with a limited number of production traits such as growth rate and survival rate. Disease resistance can also be assessed by sending tagged families to an outside laboratory for challenge trials. This allows development of SPF families that are also SPR (specific pathogen resistant).
Field trials are needed to avoid the proverbial "laboratory white mouse syndrome" in which animals bred within the biosecure confines of the NBC are poorly adapted for conditions in real production environments. Field trials involve tagging juveniles of selected families for growout to typical harvest size in production environments. Comparative performance data returns to the NBC for use in selections, but animals reared in production environments or disease challenge trials may not be returned.
Data from multiple selection criteria can be collectively assessed using a selection index. Selection criteria also consider inbreeding effects. Software is used to find the proper balance between selection of top performing families and avoidance of inbreeding.
Molecular methods can be used to quantify inbreeding, identify genetic markers for particular traits, or "finger print" stocks of a specific origin.
After production traits, breeders often target processor traits such as head to tail ratio, shell thickness, ease of peeling, and shelf life in cold storage. The most advanced criteria also consider consumer traits such as taste, texture, pigmentation, and cholesterol content.
The NBC is designed to continually produce excess broodstock for export to commercial hatcheries, but no animals may be imported into the NBC without proper quarantine.
Even with strict biosecurity safeguards, duplicate stocks should be maintained at an alternate location in the event of disease contamination.
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