Some bycatch is retained, but the global average discard rate for all shrimp trawl fisheries is more than 62 percent, over twice the rate of any other fishery . When shrimp farming first became profitable in the 1970s, it was lauded by some as a ‘Blue Revolution’, a way to avoid the environmental havoc described above. However, rapid, unregulated expansion of intensive level fish farms earned farmed seafood a reputation of being unhygienic and environmentally destructive in its own ways. Low survival rates, disease outbreaks, concentrated waste effluent, and undesirable feed ingredients soon disillusioned environmentalist support . Over the decades though, aquaculture technology has evolved considerably, resulting in sustainable feed alternatives, the ability to reduce waste, and produce more efficient, cleaner products overall. At least in countries with effective regulation. The majority of our current imports come from penaeid shrimp farms in India, Indonesia, and Ecuador ; countries with less stringent health and environmental standards than those of the U.S. One way to meet the growing domestic demand for shrimp, as well as ensure environmental integrity, is to produce our own. Marine shrimp aquaculture exists in the United States, but import statistics show that domestic products constitute a negligible amount of our annual consumption. Researchers in the 1970s looked into various shrimp species for farming along the Pacific coast, but studies were abandoned as it proved far cheaper at the time to get products from abroad and shrimp farming became dominated by warm water species . Currently,cannabis dry racks people are becoming more cognizant of the origins and environmental impacts of their food. A locally-farmed shrimp could reduce the environmental footprint of long-distance imports; provide a fresher product to the consumer; and reduce ecosystem damage resulting from farming and fishing practices in unregulated regions. Major concerns and opposition regarding fish and shellfish farming include the risk of escape and subsequent introduction of an invasive species or pathogens.The spot prawn is native to the North Pacific and to this point has never been utilized as a commercial aquaculture species.
There is an active wild capture fishery for spot prawn in California, Washington, Oregon, Alaska, and Canada. The California fishery is most active between Santa Cruz and San Diego, averaging 250,000 pounds per year. Only pots are used, as trawling for spot prawn is prohibited in all state waters. The fishery is regarded as relatively sustainable due to its small, limited access , closure during peak spawning months, and the ban of trawling . However, California spot prawn earns only a “good alternative” score from Monterey Bay Aquarium’s Seafood Watch due to potential damage to seafloor habitats caused by the traps . Furthermore, no surveys are conducted to estimate or monitor population abundance, and the bycatch to target ratio was only monitored during the 2000-2001 season where it was found to be 1:1 in the south and 2:1 in the north . Stable catch, limited access, and gear restrictions may indicate a well-managed fishery, but in reality, much of the spot prawn population health is unknown. Live spot prawns can reach $24 per pound ex-vessel price and $30 per pound at markets due to their large size – sometimes six shrimp to a pound. In Japanese restaurants the large, cold-water shrimp is known as amaebi , a high-end sushi item. Stateside Asian marketplaces are the primary consumers for California spot prawn, while the bigger fisheries in Alaska and British Columbia export a significant percentage of their landings to Japan or global sushi markets . Farming P. platycerosis not a call to derail the wild-capture fishery, but a suggestion that supplementing this seasonal fishery with a farmed option may be a prudent way to support local industry and avoid increasing ecosystem stress or competition on the water. In 1970, Price and Chew of the University of Washington Fisheries Research Institute undertook the first laboratory rearing of P. platyceros. Until this study, the only descriptions of larval stages were drawn from plankton samples in the 1930s. The culmination of their study is the definitive morphological guide to spot prawn development through stage IX. Price & Chew caught ovigerous females in Washington and reared larvae from the females and from loose eggs that had detached during transport. Loose eggs were kept suspended on a screen in a unique recirculating system with 10µ-filtered, aerated, UV-sterilized saltwater. In this setting, eggs could last up to sixty days with no fungus growth.
There is no comment as to when the detached eggs hatched in relation to the eggs carried by females, but both hatched successfully. It took females 7-10 days to release all of their progeny once hatching began. Newly hatched larvae could survive two weeks on yolk reserves alone, but were capable of feeding immediately on Artemia salina if provided. Larvae were transferred to beakers of fresh, unfiltered seawater each day. All mortalities appeared due to a failure to completely shed their molt. Each stage, defined as the period between molting, lasted an average of 9 days, with specimens reaching the post-larval stage at day 35 at 11ᵒC. Both the morphological guide and the methods of egg incubation were utilized to guide the present experiment. In the second study from this era, John Wickins investigated the influence of food density, salinity, temperature, and stocking density on the growth rate and survival of P. platyceros. Larvae hatching from females were reared in environments of 13-16ᵒC and 30±1% salinity. Development to post-larva was achieved at 15-29 days, in contrast to the 35-day span for Price & Chew; this is likely due to the warmer culturing temperatures. The stocking density yielding the highest survival rate was 5 larvae per liter at temperatures 13- 15ᵒC. Other key observations were that the size of Artemia fed to larvae did not influence larval growth rate or survival, and while larvae were raised successfully at a range of temperatures, there is a possible trend of fewer post-larvae survivors with increasing egg incubation temperature .The final major study addressing spot prawn rearing built off of those above to define the environmental extremes in which P. platyceros can thrive. Reiterating the others’ findings, Kelly et al. observed the larval period to last 26 to 35 days at 9.5-12.0ᵒC. They also concluded that spot prawns show a maximum thermal tolerance of 21.0ᵒC and salinity tolerance down to 22%. Growth rate was increased in both larvae and post-larvae by supplementing Artemia nauplii with any of four unicellular algae species. Kelly et al. also includes extensive investigation of diets for enhancing post-larvae growth, which can be an important reference for further analysis of aquaculture potential, but the scope of this study is limited to larval development. The present study attempts to reaffirm that this species can develop in laboratory settings. Using an amalgamation of the environmental parameters and timelines defined above, spot prawn larvae were hatched from ovigerous females caught off the coast of San Diego, California and cultured to post-larvae .
The current growth of the aquaculture industry in conjunction with the depletion of wild seafood stocks makes revisiting this prospective aquaculture species a timely endeavor. By culturing eggs to this critical developmental phase, this experiments aims to provide an updated assessment as to whether P. platyceros may be a viable native species for aquaculture along the Pacific coast.Adult prawns were collected opportunistically during several research trawls off the coast of San Diego, California,drying rack for cannabis totaling six males and ten ovigerous females. Specimens were held in bins of iced seawater until transport to Scripps Institution of Oceanography research aquarium. At the aquarium facility, males and females were kept together in a rectangular, aerated, flat bottomed tank with seawater at 8ᵒC, and fed a diet of fresh mussels. The SIO system provides flow-through seawater pumped from nearshore, through two sand filters to a settling tank, and gravity fed to the aquarium building. No further filtration or sterilization takes place. Upon hatching from the females, a sample of fifty larvae were transferred to a kreisel tank constructed from acrylic siding and a large PVC pipe body. The purpose of kreisel tank design is to prevent larvae from settling on the bottom by providing a constant vertical circular flow. The tank was supplied with filtered, ambient temperature seawater for the duration of the trial; no aeration was provided as the system was flow-through and kreisel tanks are well-circulated. Temperature and salinity were measured daily by sensors near the intake pump for the SIO aquarium; these were periodically checked against measurements taken in the tanks to confirm accuracy. The kreisel tank is just under 12 liters, thus a sample of fifty represents a density of approximately 4.2 larvae per liter. This density was chosen because the highest rate of survival achieved in prior studies was at 5 larvae per liter, and mortality increased with density . This stocking density is comparable to that of “extensive” level aquaculture . The tank was cleaned approximately every ten days.1 Two eggs from the initial sample of 68 hatched successfully , on April 1 and April 7. Incubation below 15ᵒC would have been preferable, but due to a broken chiller, eggs were incubated at ambient temperature. While the majority of the sample deteriorated by late March, the two survivors hatched in the same time frame that eggs were hatching from the females, despite the significantly higher incubation temperature. Larva 1 survived six days, perishing during ecdysis. Larva 2 did feed immediately but otherwise exhibited signs of abnormal development: he was not phototactic, and had less vibrant coloration than successful larvae. Larva 2 perished in 36-48 hours. The success of the eggs from the captive females in contrast to the failure of the laboratory cultivated samples implies it may be necessary to maintain ovigerous females to provide stock.
Females required minimal maintenance, being fed once daily and held at constant temperature in a flow-through system. Two of the original lab-cultured eggs hatched successfully, though neither survived through the critical period. The entire sample from the deceased female decomposed rapidly despite immediate transfer to a constant-flow setup. Price & Chew were able to successfully hatch out eggs separated from females when maintained in highly sterilized environments. Furthermore, the eggs in the laboratory were subjected to temperatures up to 10ᵒC higher than those on the females, and Wickins noted a trend of decreased survival in larvae that were incubated at higher temperatures. Thus the survival of eggs removed from females may be improved by providing a colder, more sterile culturing environment, but in this study, successful hatching depended upon healthy females for incubation. All of the surviving specimens achieved post-larval stage development by day 26. Prior studies have defined larval life as the time at which fifty percent of the sample reach post-larval stage ; in this study, the sample achieved fifty percent development to post-larvae at approximately day 20. Larvae quickly acclimated to 16ᵒC seawater after being incubated in 8ᵒC, suggesting warmer temperatures can be used to speed up development. 80 percent survival is in the upper range observed in previous studies. Wickins achieved 80 percent or higher survival in about a quarter of his trials, and Kelly et al. observed a maximum survival of 70 percent. Achieving relatively high survival in an environment where temperature fluctuated with local weather patterns confirms this species is resilient to natural variation and can develop readily in environments with unsterilized seawater sources. Further trials can be run to see how survival compares in natural seawater versus the filtered seawater used here.The filter screen of the kreisel was large enough to allow Artemia and powdered feed through to the outflow chamber. This made it impossible to conclude if water clear of food matter signified the larvae had consumed everything or if it had been flushed out. The water was typically clear before most feeds, regardless of the Artemia concentration in the prior feeding. Because of this, feed concentrations were increased to compensate for food lost through the filter and the 120kArtemia per day became a minimum guideline.