Biosecurity Protocols for Cultivated Oyster Mariculture Program

Hatchery and Seed Importation Requirements

Cultivated oysters share habitat with Texas’s native oyster species. Thus, there are strict rules in place to protect the health of both wild and farmed oysters and avoid introducing non-native species into the ecosystem. Ideally, Texas oyster growers should purchase seed from Texas hatcheries; however, at times, purchasing seed, larvae, or broodstock from out-of-state hatcheries may be necessary. In these cases, TPWD has instituted strict rules for importing and transferring out-of-state oysters at any stage in their life cycle.

Out-of-State Hatchery Requirements

Out-of-state hatcheries can only be used if they meet the following requirements:

• Products must be certified as disease free (with test results from a TPWD-approved laboratory) and of the proper genetic regional origin.

• Hatcheries must work exclusively with Gulf oysters (cannot accept oysters from the Atlantic or Pacific coasts).

• Hatcheries cannot allow oysters, seed, or larvae bound for Texas to have contact with water from organisms from the Atlantic or Pacific coasts.

Each time seed is imported from an out-of-state hatchery, the importer must first provide signed copies of the Oyster Health Certificate and Oyster Transport Chain of Custody Form to TPWD. The department must authorize the planned importation in writing before seed, larvae, or broodstock are imported into Texas.

Moving Oyster or Seed Between Sites

Regardless of where the oysters or seed come from, they cannot be stocked or moved between permitted sites (including farms, hatcheries, and nurseries) without first notifying TPWD at least seven (7) days in advance. An Oyster Transport Chain of Custody Form must be submitted to TPWD whenever oyster or seed is transported between sites. The only time the form is not required is when transporting oysters to a Certified Dealer for sale. When transporting seed between sites within Texas, follow the guidance on genetic regions below.

Genetic Regions for Texas Oysters

Texas has two distinct genetic populations of eastern oysters that only overlap in the Corpus Christi/Aransas Bay area. To protect these genetic populations, growers must take care to only use seed from the appropriate region. The seed selected depends on the site of the farm in relation to Aransas Bay and the origin of the broodstock that produced the seed (Table 1).

Importing Diploid, Triploid, and Tetraploid Oysters into Texas

Farmers must not only consider the genetic origin of oyster seed, but also the number of chromosomes — or ploidy — in their oyster stock. Wild oysters are diploid, meaning the egg and sperm cells contain two sets of chromosomes (2N). However, triploid (three sets of chromosomes; 3N) oysters are often preferred for commercial farming because they grow larger and plumper than diploid oysters and perform better during the hot summer months. Triploid oysters are usually sterile, so they cannot breed with commercial or wild stock. To get triploid oyster seed, it is common to cross a diploid with a tetraploid (oysters with four sets of chromosomes; 4N).

See Oyster 101 for more information on ploidy.

Diploid Seed Requirements

To ship diploid seed oysters into the state of Texas, the following documentation is required:

• TPWD Oyster Transport Chain of Custody Form (TPWD form PWD1439F), including:


  • Name and address of applicant (recipient; nursery or grow-out permit number)

  • Name and address of source facility (e.g., out-of-state hatchery)

  • Life stage (e.g., larvae, seed) and size (mm) of oysters to be imported

  • Quantity of each

  • The seed destination (stocking site) 

  • Geographic origin of all broodstock

    • If broodstock was harvested under a broodstock permit, the permittee must report the bay system, geographic coordinates, number of oysters harvested, and date the broodstock was sent to a hatchery for spawning.

    • See Table 1 for acceptable broodstock origins for seeds depending on the destination farm location.

• Disease testing results (Oyster Health Certificate)

Triploid/Tetraploid Seed of Broodstock Requirements

To ship triploid or tetraploid gametes, seed, or broodstock into the state of Texas, the following documentation is required:

• TPWD Oyster Transport Chain of Custody Form (TPWD form PWD1439F), including:

  • Name and address of applicant (recipient; hatchery, nursery or grow-out permit number)

  • Name and address of source facility (e.g., out-of-state hatchery)

  • Life stage (e.g., larvae, seed) and size (mm) of oysters to be imported

  • Quantity of each

  • The seed destination (stocking site)

  • Description of methods used to create the polyploid (e.g., tetraploid X diploid or chemical induction of triploid, etc.)

  • Ploidy (triploid or tetraploid)

  • Ploidy testing results from a representative sample of seed purchased and description of how ploidy of seed was tested

  • Geographic origin of broodstock for triploid seed

    • If broodstock was harvested under a broodstock permit, the permittee must report the bay system, geographic coordinates, number of oysters harvested, and date the broodstock was sent to a hatchery for spawning.

    • See Table 2 for acceptable genetic origins for triploids.

Texas Oyster Seed Disease Testing Requirements

To avoid introducing diseases into the wild and captive oyster populations, all oysters imported into Texas from other states must be tested for the following pathogens:

• MSX (Haplosporidium nelsoni)

• Dermo (Perkinsus marinus)

• Bonamiosis (Bonamia exitiosa)

• Oyster Herpes Virus (OsHV-1)

Each batch (same seed lot, same producer, and held in the same environment) of oyster seed, larvae, or broodstock brought into Texas must undergo two types of disease testing by a TPWD-approved laboratory (Table 3):

1. Microscopic (histological) testing

   1. A representative sample (n = 60) of the seed, larvae, or broodstock to be imported must be processed to produce microscope slides showing all major tissue types.

   2. Slides must be read by an invertebrate pathologist.

   3. All evidence of disease (MSX, Dermo, Bonamiosis and others) found within the tissue must be reported.

2. Specialized testing for Dermo

   1. A representative sample (n = 60) of seed, larvae, or broodstock to be imported into Texas must be tested for the presence of Perkinsus marinus (Dermo) using Rays Fluid Thiglycollate Media (RTFM), PCR or qPCR techniques

Oyster Health Certificate

Anyone planning to import oysters into Texas must first submit an Oyster Health Certificate to TPWD. The Oyster Health Certificate should include the following:

• Dated and detailed pathology report, including the results for each pathology test and a description of the methods used

• Name of the hatchery from which the seed originated

• Certification case number

• Certification date

To qualify for approval, oyster seed, larvae, or broodstock can have a maximum prevalence of 10% for Dermo and zero for all other parasites or disease. Oyster Health Certificates are valid for 30 days after testing.