Closed System Culture of Penaeus vannamei

Penaeus vannamei were cultured utilizing three different closed recirculating seawater systems. The first system used biological filtration for water treatment. The second system utilized both physical and chemical filtration, but no biological filtration. The third system used a combination of biological, physical, and chemical filtration. Shrimp growth was monitored for a 12-week period for each system. Shrimp from the biological filtration system had a growth rate of 0.82 g/wk and an overall survival rate of 45.6%. Shrimp from the closed system which used physical and chemical filtration had a growth rate of 0.99 g/wk and a survival rate of 29.2%. In the third system which combined both types of filtration, the shrimp growth rate averaged 0.65 g/wk and the survival rate was 56.9%

Comparing Salinities of 10, 20, and 30% in Intensive, Commercial-Scale Biofloc Shrimp (\u3ci\u3eLitopenaeus vannamei\u3c/i\u3e) Production Systems

Minimal-exchange, intensive biofloc aquaculture systems offer a viable means of culturing marine animals at inland locations due to very low rates of water use. Fresh, never-frozen shrimp can be provided to metropolitan markets; however, the cost of artificial salt can be substantial. The purpose of this project was to examine commercial-scale biofloc shrimp production at three different salinities. Nine raceways were randomly assigned to three salinity treatments: 10, 20, and 30‰ (LS, MS, and HS), each treatment contained three raceways operated at 50 m3. The raceways were operated as heterotrophic biofloc systems, with daily additions of sucrose to raise the C:N ratio. Temperature, dissolved oxygen, pH, and salinity were all maintained at consistent levels. Spikes of ammonia and nitrite occurred in all tanks but nitrate remained low, with a peak value of 8.7 mg NO3-N L− 1. There were no significant differences in any shrimp production metric. Mean shrimp growth rate was 1.8, 2.0, and 2.0 g week− 1 in the LS, MS, and HS treatments respectively. Mean feed conversion rate was 1.6, 1.2, and 1.2 in the LS, MS, and HS treatments respectively, and mean final weight ranged from 17.8 to 19.3 g. The only time water was removed from the systems was when settling chambers were emptied, resulting in a total mean water replacement of 5.2% or less per raceway. The mean volume of full strength seawater used to produce shrimp was 104, 159, and 235 L kg− 1 of shrimp in the LS, MS, and HS treatments respectively. Although there were no significant differences in shrimp production metrics between treatments, these values were noticeably lower in the LS treatment due to human error. Operating at the low salinity of 10‰ reduces salt use by about 50% over the MS treatment which implies substantial cost savings for production facilities. This study helps to illustrate the range of salinity options for shrimp production in commercial-scale biofloc systems

Closed System Culture of Penaeus vannamei

Penaeus vannamei were cultured utilizing three different closed recirculating seawater systems. The first system used biological filtration for water treatment. The second system utilized both physical and chemical filtration, but no biological filtration. The third system used a combination of biological, physical, and chemical filtration. Shrimp growth was monitored for a 12-week period for each system. Shrimp from the biological filtration system had a growth rate of 0.82 g/wk and an overall survival rate of 45.6%. Shrimp from the closed system which used physical and chemical filtration had a growth rate of 0.99 g/wk and a survival rate of 29.2%. In the third system which combined both types of filtration, the shrimp growth rate averaged 0.65 g/wk and the survival rate was 56.9%

Gonadal Maturation in the Cobia, Rachycentron canadum, from the Northcentral Gulf of Mexico

Gonadal maturation of cobia, Rachycentron canadum, was evaluated by examining 508 specimens from its recreational fishery. Specimens were collected off southeast Louisiana to northwest Florida by hook-and-line during February through October 1987-1991. Fork lengths (FL) of these fish ranged from 580-1,530 mm, with corresponding weights of 2.0-43.5 kg. The female:male ratio was 1:0.37. Using a combination of oocyte size frequency and histological assessment of many of the fish, we determined that females were ripe from May through September, with atretic oocytes occurring in some fish from July through October. Degenerating hydrated oocytes in July and October and the presence of resting ovaries in July suggest two major spawning periods; however, monthly gonosomatic indices peaking in May, followed by a steady decline, do not support that finding. Ovaries were placed into undeveloped, early developing, mid-developing , or late developing categories based upon oocyte size-frequency distributions. Developing ovaries had two or three modes of oocytes larger than 30 pm. Batch fecundity was estimated to be 2.6x106 to 1.91x108 oocytes, depending on the size of fish/ovaries. The smallest female with oocytes exhibiting vitellogenesis was 834 mm FL. This fish was 2 years old based its otolith evaluation. The smallest male with an abundance of spermatozoa in its testes was 640 mm FL and 1 year old based on otolith evaluation; smaller males were not examined. Females larger than 840 mm FL had vitellogenic oocytes in March and April. A few fish still had vitellogenic oocytes in early October, but none did by late October. When Gilson’s fluid was used to assess ovarian tissue, the fresh weight of the tissue was reduced by 20% after being stored for 3 months. The diameter of oocytes shrunk about 25% in Gilson’s fluid which was 11% less than those fixed in formalin, embedded in paraffin, and sectioned. Tissue sections from specific individuals, each demonstrating a variety of different developmental stages, were similar regardless of whether they were obtained from the anterior, middle, or posterior portion of either ovary

Effects of Salinity on Survival and Growth of Postlarval Penaeus vannamei

Eight and 22-day-old Penaeus vannamei postlarvae were exposed to several salinities for 24 hours and 120 hours by direct transfer from 32 ppt salinity to lower salinity waters. The challenge study included six experiments conducted on 8-day-old postlarvae (PL-8) and five experiments conducted on 22-day-old postlarvae (PL-22). Each experiment consisted of ten replicates of ten animals each. Shrimp were held in 1 L plastic containers with 500-ml of seawater. Lowered salinity resulted in lower survival for shrimp of both ages. Longer exposure time resulted in lower survival for shrimp of both ages. Younger shrimp exhibited lower survival than older shrimp. Survival of 8-day-old postlarvae after 24-hour exposure to salinities of 32, 16, 8, 4, and 2 ppt was 97.3%, 92.8%, 19.8%, 8.2% and 1.7%, respectlvely. Survival of 22-day-old postlarvae after 24-hour exposure was 99.2%, 97.8%, 83.8%, 63.4% and 40.2%, respectively. A second series of experiments investigated the effect of salinity upon growth of 22-day-old postlarvae which had been acclimated to four different salinities (16, 8, 4, and 2 ppt). Thirty shrimp were stocked in triplicate into 113 L (30 gal) aquaria and fed a prepared commercial feed. Growth was determined after 30 days at 16oC and 28-30oC. Growth was greatest at higher temperatures, but statistically significant differences due to salinity were not detectable. Nonetheless, best observed growth occurred at the intermediate salinities of 8 and 4 ppt

Gonadal Maturation in the Cobia, Rachycentron canadum, from the Northcentral Gulf of Mexico

Gonadal maturation of cobia, Rachycentron canadum, was evaluated by examining 508 specimens from its recreational fishery. Specimens were collected off southeast Louisiana to northwest Florida by hook-and-line during February through October 1987-1991. Fork lengths (FL) of these fish ranged from 580-1,530 mm, with corresponding weights of 2.0-43.5 kg. The female:male ratio was 1:0.37. Using a combination of oocyte size frequency and histological assessment of many of the fish, we determined that females were ripe from May through September, with atretic oocytes occurring in some fish from July through October. Degenerating hydrated oocytes in July and October and the presence of resting ovaries in July suggest two major spawning periods; however, monthly gonosomatic indices peaking in May, followed by a steady decline, do not support that finding. Ovaries were placed into undeveloped, early developing, mid-developing , or late developing categories based upon oocyte size-frequency distributions. Developing ovaries had two or three modes of oocytes larger than 30 pm. Batch fecundity was estimated to be 2.6x106 to 1.91x108 oocytes, depending on the size of fish/ovaries. The smallest female with oocytes exhibiting vitellogenesis was 834 mm FL. This fish was 2 years old based its otolith evaluation. The smallest male with an abundance of spermatozoa in its testes was 640 mm FL and 1 year old based on otolith evaluation; smaller males were not examined. Females larger than 840 mm FL had vitellogenic oocytes in March and April. A few fish still had vitellogenic oocytes in early October, but none did by late October. When Gilson’s fluid was used to assess ovarian tissue, the fresh weight of the tissue was reduced by 20% after being stored for 3 months. The diameter of oocytes shrunk about 25% in Gilson’s fluid which was 11% less than those fixed in formalin, embedded in paraffin, and sectioned. Tissue sections from specific individuals, each demonstrating a variety of different developmental stages, were similar regardless of whether they were obtained from the anterior, middle, or posterior portion of either ovary

Susceptibility to Taura Syndrome Virus of Some Penaeid Shrimp Species Native to the Gulf of Mexico and the Southeastern United States

Experimental studies demonstrated that Penaeus setiferus, but not Penaeus aztecus or Penaeus duorarum, could be killed by Taura syndrome virus (TSV). However, specimens of P. setiferus that survived infection and both P. aztecus and P. duorarum at least 79 days postexposure that did not demonstrate gross signs of infection were shown to harbor virus by bioassay using Penaeus vannamei, a highly susceptible target host. Consequently, all three of those penaeids native to the southeast United States can serve as carriers or reservoir hosts of TSV without necessarily exhibiting disease. Infections in P. setiferus took longer to cause mortality than in P. vannamei and killed a smaller percentage of that host. Also, histological lesions diagnostic of TSV infection were not always evident in sectioned tissue of infected P. setiferus, and they generally were more conspicuous during Days 4–7 postexposure compared with lesions that also occurred at both earlier and later days in tissues of P. vannamei. Infections could be produced by injection, ingestion, and incorporation of the infective material into dietary brine shrimp. There appeared to be a difference in susceptibility to TSV disease by different stocks of P. setiferus, but different experiments produced conflicting evidence regarding a relationship between age and predilection to mortality. Large and small specimens of equal-aged shrimp succumbed similarly to TSV infections for both P. vannamei and P. setiferus. The nonnative species P. chinensis demonstrated a high susceptibility to experimental TSV disease

Reproductive Biology of Cobia, Rachycentron canadum, from Coastal Waters of the Southern United States

Reproductive biology of the cobia, Rachycentron canadum, is described from four coastal areas in the southern United States. Samples were obtained from recreational fishermen between December 1995 and November 1997 from the southeastern United States (Morehead City, NC, to Cape Canaveral, FL), the eastern Gulf of Mexico (Ft. Myers to Crystal River, FL), the north-central Gulf of Mexico (Destin, FL, to Chandeleur Islands, LA) and the western Gulf of Mexico (Port Aransas, TX). Histological evidence of spawning occurred from April through September in all areas. Some female cobia (17-32%) throughout the Gulf of Mexico had spent or regressed ovaries by July. Gonadosomatic index peaked between May and July throughout the region. Ovaries of females from all areas contained both postovulatory follicles (POF) and oocytes in final oocyte maturation (FOM) during all months of the reproductive season. Batch fecundity was calculated by using three different methods: oocytes \u3e700 pm were fixed in 1) Gilson\u27s fixative or 2) 10% neutral buffered formalin (NBF), and 3)oocytes undergoing FOM were sectioned for histological examination. Mean batch fecundity ranged from 377,000 +/- 64,500 to 1,980,500 +/- 1,598,500 eggs; there was no significant difference among methods. Batch fecundity calculated with the NBF method showed a positive relationship with fork length (P=0.021, r(2)=0.132) and ovary-free body weight (OFBW; P=0.016, r(2)=0.143). Relative batch fecundity was not significantly different among months during the spawning season and averaged 53.1 +/-9.4 eggs/g OFBW for the NBF method and 29.1 +/- 4.8 eggs/g OFBW for the FOM method. Although spawning frequencies were not significantly differ ent among areas (P=0.07), cobia from the southeastern United States and north-central Gulf of Mexico were estimated to spawn once every 5 days, whereas cobia from the western Gulf of Mexico were estimated to spawn once every 9 to 12 days

Reproductive Biology of Cobia, \u3ci\u3eRachycentron canadum\u3c/i\u3e, from Coastal Waters of the Southern United States

Reproductive biology of the cobia, Rachycentron canadum, is described from four coastal areas in the southern United States. Samples were obtained from recreational fishermen between December 1995 and November 1997 from the southeastern United States (Morehead City, NC, to Cape Canaveral, FL), the eastern Gulf of Mexico (Ft. Myers to Crystal River, FL), the north-central Gulf of Mexico (Destin, FL, to Chandeleur Islands, LA) and the western Gulf of Mexico (Port Aransas, TX). Histological evidence of spawning occurred from April through September in all areas. Some female cobia (17-32%) throughout the Gulf of Mexico had spent or regressed ovaries by July. Gonadosomatic index peaked between May and July throughout the region. Ovaries of females from all areas contained both postovulatory follicles (POF) and oocytes in final oocyte maturation (FOM) during all months of the reproductive season. Batch fecundity was calculated by using three different methods: oocytes \u3e700 μm were fixed in 1) Gilson’s fixative or 2) 10% neutral buffered formalin (NBF), and 3) oocytes undergoing FOM were sectioned for histological examination. Mean batch fecundity ranged from 377,000 ± 64,500 to 1,980,500 ± 1,598,500 eggs; there was no significant difference among methods. Batch fecundity calculated with the NBF method showed a positive relationship with fork length (P = 0.021, r2 = 0.132) and ovary-free body weight (OFBW; P = 0.016, r2 = 0.143). Relative batch fecundity was not significantly different among months during the spawning season and averaged 53.1 ± 9.4 eggs/g OFBW for the NBF method and 29.1 ± 4.8 eggs/g OFBW for the FOM method. Although spawning frequencies were not significantly different among areas (P = 0.07), cobia from the southeastern United States and north-central Gulf of Mexico were estimated to spawn once every 5 days, whereas cobia from the western Gulf of Mexico were estimated to spawn once every 9 to 12 days