Use of Probiotics to Increase Survival and Sustainable Yield of Inland Farmed Shrimp

View the project final report

Commodities

• Animals: fish

Practices

• Animal Production: animal protection and health, inoculants, preventive practices, probiotics
• Crop Production: biological inoculants
• Education and Training: extension, farmer to farmer, on-farm/ranch research
• Farm Business Management: budgets/cost and returns, agricultural finance
• Pest Management: biological control
• Sustainable Communities: local and regional food systems, sustainability measures

Statement of Problem

Our 4 cooperating farms together have produced 600,000 lbs of shrimp in a year.  This year (2016) total production was 400,000 lbs.  Production is lower because shrimp survival and corresponding production has decreased during the past 2 to 3 years.  Several marine shrimp farms in Texas are experiencing similar problems as we have (Granvil Treece, Retired, Sea Grant; personal communication).  If our survivals remain this low, we will not be able to remain in business.

Shrimp survival has always been a concern of us farmers. We stock only specific pathogen free seed stock that are certified to be free of viruses and one bacterial disease that commonly affect farmed shrimp.  Even so, baby shrimp are so small that they can succumb early in life without the farmer seeing the immediate effect.  During the past 3 years we have seen a decrease in survival of shrimp both at the post larval (baby) stage and most noticeably during the last 6 weeks before harvest.  A limited number of shrimp have been evaluated histologically and found to contain moderate levels of pathogenic Vibrio bacteria that are well known to reduce production or kill shrimp at high infection rates.  Vibrio is a common problem in Texas shrimp culture, but we have not seen obvious signs of disease before now in Alabama. 

Problems present themselves as a daily attrition of floating dead animals on the windward side of ponds.  Once the mortality begins, it usually does not end until harvest.  Sometimes there is more acute mortality that happens over a several day period.  The acute mortality is almost always associated with heavy blooms of certain species of blue-green algae known to produce toxins that may affect shrimp if at sufficiently high concentration.   Genera of Psuedoanabenna, Oscillatoria and Prymnesium, a golden algae, have been identified.  These algae seem to release toxins as they die, because shrimp mortality usually occurs during partial or complete mortality of the algae.  If shrimp are already weakened by a low level of Vibrio, then they are more likely to succumb to other environmental stressors such as phytotoxins. 

We sell our shrimp fresh to individuals at the farm, restaurants, and retail stores.  Some of us sell a large amount of our shrimp as a frozen processed product to a natural foods market.  Most of our clientele desire chemical-free shrimp that have been raised locally without antibiotics and pesticides.  Herbicides are available to limit the blooms of noxious algae, and possibly reduce the incidence of Vibrio infection. However, we require alternative, non-chemical ways to resolve our problems and be sustainable.  The resolution of the problem will require an ecosystem approach, because shrimp health is directly impacted by pond environmental conditions.

The use of live biota, or probiotics, to confer a health benefit on target animals has been gaining traction in the aquaculture world. The probiotic usually is bacterial or other single celled organism such as yeast.  We propose to use a mixture of three Bacillus species that are known to increase growth and survival in shrimp by direct consumption, but are also known to reduce organic loads in ponds by consuming organic matter.  The mode of action is not absolutely known, but consumed bacteria tend to outcompete and inhibit growth of pathogenic bacteria, and stimulate the shrimp immunosystem.  The reduction of organic matter in the pond environment is thought to limit substrate for pathogenic bacteria, as well as limit regions of low oxygen that might adversely affect shrimp.  Observational data indicate that use of this probiotic material can also reduce the incidence of blue-green algae.   Bacillus sp. has the great advantage of forming spores that can be dried and stored for later application.  Upon hydration, the spores rapidly form bacteria to populate their environment.

These probiotics are routinely used in hatcheries and nurseries to limit disease incidence and promote growth, but tests for effectiveness in grow-out ponds are limited.  Probiotics tend to be specific for various pathogens and environments, so effectiveness may not be equal across farms in different soil types and environments.  We propose to test this probiotic on three farms in Alabama and one farm in northwest Florida in order to more robustly evaluate effectiveness.  We will follow protocols that have observationally increased survival in similar environments.  We do not expect the probiotics to eliminate our problems, but to decrease their severity.  The cost of probiotic use would then be contrasted with increased production and income.

Approach and Methods

We will use a product formulated by INVE Aquaculture that guarantees a live bacterial concentration of 5X10⁵ colony forming units per gram (CFU/g).  The probiotic is added as a dried product weekly to nursery tanks and ponds at a rate of 80 g/acre-meter of water. 

We intend to evaluate the effectiveness of probiotic on shrimp health, water quality and type and density of blue-green algae.  The primary determinant will be survival and growth of stocked shrimp, which depends directly on good shrimp health and a good growing environment.  Shrimp health will be evaluated by direct quantification of infection by pathogenic Vibrio sp. and by analysis of tissue for disease.  Environmental conditions will be evaluated by repeated measures of water for selected metabolites and algae.  Each farm will have ponds treated with probiotics and other control ponds that are stocked with similar rates of shrimp, but to which no probiotics have been added.  We will have a total of 13 treatment ponds and 13 control ponds among 4 farms.  One farm, Greene Prairie Aquafarm, will have 4 treatment and 4 control ponds.  Gulf American Shrimp, Forkland Springs, and Odom Farms will each have 3 treatment and 3 control ponds. 

Samples of water from each treatment and control pond will be evaluated for Vibrio sp. once a month starting at stocking.  Each month, 10 shrimp from each treatment and control pond will be evaluated for Vibrio sp.  Twice during the season, once half way through in July, and the other just before harvest, 10 shrimp from each treatment and control pond will be evaluated histologically for disease.  Shrimp health evaluations will be conducted by Dr. Susan Laramore at her lab at Harbor Branch Institute/Florida Atlantic University.

Water samples will be collected weekly from each of the treatment and control ponds to be analyzed for total ammonia and nitrite.  These are metabolites that can harm shrimp if in too high a concentration.  Water quality analyses will be done in the laboratory of the Alabama Fish Farming Center near the Alabama shrimp farms, or on farm at Wood Fisheries.  Late afternoon pH will be measured in situ at 24 inches of depth in all study ponds once a week by cooperating farmers. 

Phytoplankton (microscopic pond algae) samples will collected every other week from each treatment and control pond to be analyzed for type and relative quantity of blue-green algae.  Algae evaluation will be conducted by personnel at the Alabama Fish Farming Center with assistance by personnel at Auburn University School of Fisheries.

All farms will keep track of the following information concerning each treatment and control pond: number of shrimp stocked, total feed input, total number of shrimp harvested and total weight of shrimp harvested.  Observations on mortalities and other pertinent information will be kept throughout the production season.