Stocking density evaluation on Catarina scallop (Argopecten ventricosus,Sowerby II, 1842) larvae to improve hatchery production

The Catarina scallop Argopecten ventricosus is a highly valued resource. Although its hatchery spat production has already been reported, the effects of initial larval stocking density have never been reported for production purposes. This study evaluates A. ventricosus growth and survival in triplicate using three stocking densities: low (LD; 2 larvae mL^?1), medium (MD; 4 larvae mL^?1), and high (HD; 6 larvae mL^?1). Three-day old larvae were reared in 18-L plastic carboy at 25.6?±?0.5 °C and fed with a microalgal blend of Isochrysis galbana and Chaetoceros calcitrans (1:1 cell number ratio) for 7 days, equivalent to 10 post-fertilization days (PFD). Higher specific growth rate was recorded at LD (15.8?±?0.2%) after 8 PFD of culture compared to MD (1.6?±?0.5%) and HD (4.1?±?1.8%) densities. The least time required for 60% of the larvae to reach the pediveliger stage was recorded at LD condition (10 PFD). Higher survival was recorded at HD (58.8?±?3.1%) at 8 PFD compared to MD (53.5?±?3.1%) and LD (43.9?±?3.0%). After 8 PFD, stocking density was highly related to larval growth and survival. To increase production and growth, and reduce the time required to reach pediveliger stage, stocking density should start with 6 larvae mL^?1 and be reduced to 2 larvae mL^?1 at 7 PFD.

     

Effects of mass and position of artificial fouling added to the upper valve of the mangrove oyster Crassostrea rhizophorae on its growth and survival

We ran an experiment on mangrove oysters Crassostrea rhizophorae to evaluate the effects of adding different masses of artificial fouling to the upper valve, either to the umbo region or the ventral edge of the shell. Growth and survival were quantified after a 30 d period in suspended culture in the La Restinga Lagoon, Venezuela. The artificial fouling was cement weighing 0.5, 1, 2 or 3 fold the mass of the upper valve. No fouling was added to a control group. Fouling mass, but not the position of the artificial fouling, affected growth in shell length. However, only the heaviest fouling (3 times the mass of the upper valve) had a significant effect. In contrast, there was no affect of either fouling mass or position on tissue growth. Finally, our data indicated that mortality could be affected by the position where we added artificial fouling (greater mortality when fouling was added to the ventral edge of the shell), but not by fouling mass. Our study indicates it is unlikely that the levels of natural fouling that develop on oysters in suspended culture would be sufficient to affect either growth or survival.     

Mass production of competent larvae of the sea urchin <Emphasis Type="Italic">Lytechinus variegatus</Emphasis> (Echinodermata: Echinoidea)

We evaluated the mass production of competent larvae of the sea urchin Lytechinus variegatus cultured at three initial densities (0.25, 0.5, and 1 larvae per ml) and fed Chaetoceros muelleri. Survival, length, dry weight of larvae, and larval stage index (LSI) were estimated in each treatment as a function of the density. Density decreased during the experiment due to mortality, but the percentage was similar in all three treatments (68.5, 66.7, and 76.0%). The experiment was stopped at 13 days after fertilization, when most of the larvae were competent and had settled. There were no significant differences in survival (exceeded 65% in all treatments), length and larval stage index among treatments. However, larvae weight in the two low density treatments (1.1 ± 0.11 mg and 1.2 ± 0.05 mg, respectively) was greater than the high density treatment (0.59±0.376 mg). This study demonstrates that competent larvae of Lytechinus variegatus can be produced with less than 25% mortality in 13 days when cultures are started at densities of 0.25–1 larvae/ml. Culturing at higher densities (0.5–1 larvae/ml) had no apparent disadvantages and would reduce the cost of production.     

Growth and survival of the pearl oyster Pinctada imbricata (Röding 1758) in supended and bottom culture in the Golfo de Cariaco, Venezuela

We evaluated growth and survival rates of Pinctadaimbricata in relation to environmental changes during nine months insuspended and bottom culture in the Golfo de Cariaco, Venezuela. Juveniles,measuring 13 mm in length, were cultured using two methods, (1) inSpanish-type baskets suspended at 3–4 m in depth from a longline and (2) in baskets embedded on the seabed (7–8 m indepth). At monthly intervals, we quantified mortality and took a sample ofoysters to determine shell length (dorsal-ventral axis) and the dry mass of theshell, muscle and remaining tissues. We also quantified the dry mass of foulingon the shells (a potentially important environmental factor). Survival rateswere slightly higher in suspended culture (98–100%), although notsignificantly higher than on the bottom. The growth rate was higher in suspendedculture than on the bottom culture, and the difference between culture methodswas greater for tissue and shell biomass than for shell dimensions. At the endof the study, oysters measured 55 mm in shell length for oysters insuspension and 45 mm for those on the bottom. Although growth wasnot significantly correlated with any environmental factor, it tended toincrease with increases in chlorophyll a during periods ofupwelling, thus suggesting that phytoplankton abundance enhanced the growth ofPinctada imbricata. The pearl oyster Pinctadaimbricata should be an excellent species for aquaculture activities,given its high rates of growth and survival in suspended culture and itseconomic importance in the Caribbean region.     

Bottom culture of the tropical scallop Lyropecten (Nodipecten) nodosus (L.) in the Golfo de Cariaco, Venezuela

Growth and survival of scallop Lyropecten nodosus were studied fromJuly to November 1997 using three bottom culture methods, (1) in corrals,(2) in pockets, and (3) in anchored sleeves. All size parameters studied (dryweight of the muscle, gonad, remaining tissues and shell, and shell length)showed significant differences due to culture method. The body componentswere larger for scallops in corrals than for those in pockets and greater forthose in pockets than in sleeves. In contrast, survival did not vary withculture method. Tissue components increased rapidly during the first 2months, when temperatures were lower and phytoplankton abundant(upwelling and transition periods). Subsequently values leveled off, or insome cases (muscle) decreased, and this coincided with stratification of thewater column and associated high temperatures and scarce food resources(and possible energetic demands for gonadal development). In contrast,shell weight and length showed no apparent affect of the environmentalchanges. The increased growth in the corrals was possibly because thecorral walls permitted the scallops to raise themselves off the bottom whichcould have provided greater access to food resources (suspendedparticles), or to better quality food.     

Evaluation of microalgae diets for Litopenaeus vannamei larvae using a simple protocol

We evaluated native marine microalgae isolated from NortheasternVenezuela, as food for Litopenaeus vannamei larvae,compared to six microalgae commonly used in aquaculture. We evaluated themicroalgal ingestability calculating the biomass consumed by larvae, later weevaluated three monoalgal diets on protozoea stages of L.vannamei over 72 hr based on the larval biomass,RNA/DNAindex and the proportion of stage retarded larvae. The presence of everymicroalgae species in the protozoea's digestive tract indicated theirconsumption. Chaetoceros spp. showed high ingestabilityandTetraselmis spp. and Skeletonema sp.Ch1 showed low ingestability. The native microalgaeChaetoceros sp. A1 and Chaetocerossp.G1 were evaluated as monoalgal diets compared to Chaetocerosgracilis. Ch. gracilis demonstrated the bestresults when the evaluation was performed with the RNA/DNA index. However, thesurvival rate, larval biomass and percentage of stage retarded larvae fed withChaetoceros sp. G1 were not statistically different fromthose fed with Ch. gracilis. Taking into account thatnative microalgae produced higher biomass in shorter times when they werecultured in field conditions, the results suggest that native microalgae areadequate for large-scale culture conditions, thus reducing costs. Thedetermination of microalgal size and the larval consumption, dry and organiclarvae biomass and specially the RNA/DNA index, were valuable features of thisevaluation. The protocol developed in this study could be used to evaluatemicroalgae quality under different environmental conditions and productionregimes.     

Growth and survival of the winged pearl oyster Pteria sterna (Gould, 1851) in suspended culture in the tropical Eastern Pacific: Influence of environmental factors

The growth, survival and influence of environmental factors were analysed in two cohorts of cultured Pteria sterna in Ayangue Bay, Province of Santa Elena, Ecuador (tropical Eastern Pacific). Juveniles representing cohorts I and II (8.4 ± 0.54 and 5.0 ± 0.17 mm in dorso‐ventral axis) were deployed in November 2015 and February 2016, and grown in pearl nets suspended in a long line for 12 and 10 months respectively. The stocking density was monthly and bi‐monthly reduced during sampling of individuals to determine growth in dorso‐ventral shell axis, dry mass of shell, soft tissues and dry mass of fouling on shell. Water temperature, salinity, total seston and phytoplankton biomass (chlorophyll a) were determined at the culture site. Results showed that P. sterna reached ~100 mm in length during the first year of culture. Although little negative influence of environmental factors was detected, high temperatures during the reproduction period can be the most negative influential trait. The highest tissue mass (6 g), which occurred at the 10th month of cultivation, as well as a high availability of spat by artificial collectors in the coastal waters, showed that the species can be considered a good candidate for aquaculture in the tropical eastern Pacific.     

Suspended culture evaluation of Pacific oyster Crassostrea gigas in a tropical estuary

The growth and survival of Crassostrea gigas were evaluated in hanging culture in the Chone River estuary (Bahía de Caráquez), Manabí province, Ecuador. Oyster seeds (~10 mm) were confined in lantern nets at a density equal to the occupation of half the surface of the basket base, until reaching commercial size (80 mm). A sample for oyster biometric, parasitic and bacterial analysis was obtained monthly. Temperature, salinity, oxygen concentration, seston and phytoplankton biomass were determined. At the end of the study, the oysters were analysed for heavy metal concentration. The commercial oyster production was extrapolated to estimate the possible economic performance of a family production module (a 7 × 7 m bamboo raft). The results show a great biological feasibility of culture of C. gigas with harvests of commercial size oysters in only 5 months and acceptable survivals (accumulated >70%, after 3 weeks of crop seed selection). The heavy metal concentrations and the parasitological and bacteriological analyses did not indicate levels of contamination. The economic projections suggest that, even with a profitability of 57%, the initially invested capital could be recovered within the first harvest.     

Influence of fouling on the growth and survival of the tropical scallop, Euvola (Pecten) ziczac (L. 1758) in suspended culture

To examine the impact of fouling organisms on the growth and survival of the scallop Euvola ziczac L., we maintained 31-34-mm juveniles in pearl nets at 8 m in depth at Turpialito, Golfo de Cariaco, Venezuela. The experiment ran for a 67-d period under four conditions: (1) shells and nets cleaned; (2) shells not cleaned and nets cleaned; (3) shells cleaned and nets not cleaned; and (4) shells and nets not cleaned. The growth of the scallop was least when fouling developed on both the pearl nets and scallop shells. The rate of growth of the shell (height and mass) was strongly affected by organisms colonizing the pearl nets and only weakly affected by organisms colonizing the shells. Fouling organisms on the shells only slightly affected rates of increase of tissue mass, but probably accounted for increased mortality. In developing commercial culture of E. ziczac, strategies need to be developed to limit the adverse effects of fouling on yield.