Giving his presentation at Aquaculture America last week, Benjamin Moll, Aonori Aquafarms, explained that shrimp readily eat ulva, which is high in protein, and therefore only a small amount of pelleted feed to supplement is needed.
As a floating crop, ulva takes up the waste C02, ammonia, phosphate, nitrogen and other mineral nutrients produced by shrimp, therefore keeping the water in the system very clean and clear.
Mr Moll noted that originally the study used vannemai shrimp in Sinaloa, Mexico but, as the water temperatures were very high (around 35ºc), it was not suitable for ulva, which has a temperature range of (12-30ºc). To overcome this problem, native brown shrimp (farfantepenaeus californiensis) were used instead, as they prefer 20-30ºc, and the study was relocated in San Quintin, Mexico with the ponds housed in greenhouses.
Overall, the system proved to be very sustainable and performed well. The use of ulva lowered feed costs and its excellent nitrogen efficiency meant that nitrogen did not leave the system as effluent, meaning there was no pollution from water discharge.
The researchers also found that female shrimp produced around 200,000-400,000 eggs each and the shrimp proved successful as breeders, meaning that wild stock did not need to be used.
Other benefits of the system included the antiviral effects of ulva, a low disease risk, low water exchange and no risk of escapes. There was also a good survival rate of 60 per cent.
Although the shrimp did not have fantastic growth rates, Mr Moll said the low production cost and the high quality of the product justified the system.
