Luis Freites

Growth and survival of the tropical scallop Lyropecten (Nodipecten) nodosus maintained in suspended culture at three depths

Abstract We examined growth and survival of juvenile Lyropecten (Nodipecten) nodosus, measuring 9.4 mm in shell height, which were placed in mid-December 1993 in pearl nets at 8, 21 and 34 m in depth at Turpialito in the Golfo de Cariaco, Venezuela. The mean growth rate in shell height during the first 5 months varied inversely with depth (10.0, 8.5 and 5.0 mm mon−1 at 8, 21 and 34 m in depth, respectively). Somatic tissues also showed a progressively slower growth rate with increasing depth. The decreased growth rate with depth was not associated with the mass of total seston or its organic content but were proportional to the decrease in phytoplankton biomass with depth (chlorophyll a decreased from 4.8 to 0.7 μg l−1 between 8 and 34 m). Temperature also decreased with depth but the differences were likely too slight to account for differences in growth. Mortality varied markedly with depth. There was a sharp increase in mortality in July at 34 m and a total mortality in August at 8 m. In contrast, at 21 m survival was high throughout the study. After 5 months (in May), wet muscle mass of the scallops at 8 m attained the commercial size (5–6 g). A possible culture strategy for L. nodosus is to initially grow the scallops at 8 m in depth, where growth is greatest, and then transfer them to 21 m, where survival is greatest and where growth will continue at a moderate rate to a larger size.

Growth of the tropical scallop, Euvola (Pecten) ziczac, in bottom and suspended culture in the Golfo de Cariaco, Venezuela

Abstract We compared the growth of the scallop Euvola (Pecten) ziczac (L.) in three situations which potentially could be used for commercial culture, in cages maintained in suspension, in cages on the bottom and in cages partly buried in a sediment bottom. The latter permitted the scallops to bury themselves as in their natural habitat. Throughout the 7-month study, growth, as measured by shell length and muscle mass, was by far superior for scallops in the partly buried cages. Possible explanations for this are (1) that the scallops are stressed by enclosures which prevent them from burying themselves and (2) that organic material at the sediment/water interface is an important food resource and E. ziczac has better access to this when it buries itself flush with the bottom. The timing of gonadal growth and spawning varied markedly among treatments. Some spawnings coincided with temperature increases but others did not. Differences between scallops in suspension compared to those in bottom treatments suggested that reproduction is as much controlled by conditions in the immediate environment of the scallops as by large-scale environmental factors. Survival was highest for the scallops maintained in partly buried cages.

Impact of predation by gastropods and crabs recruiting onto culture enclosures on the survival of the scallop Euvola ziczac (L.) in suspended culture

Abstract We evaluated the impact of predation from carnivores settling onto suspended culture enclosures on the production of scallops, Euvola ziczac , in the Golfo de Cariaco, Venezuela. Seven potential predator species were found on 70 pearl nets which were immersed from mid-February to mid-April 1994. The crabs Mythrax forceps and Pilumnus caribbaeus and the gastropod Cymatium poulseni , were found on a high proportion of the nets (56, 44 and 48%, respectively). Studies in which the various potential predator were maintained in pearl nets with 25 scallops indicated that six of the seven predators would cause significant mortality within 30 days. A single P. caribbaeus or C. poulseni destroyed 22–25 of the 25 scallops in 30 days. Observations in aquaria of attacks by three species of Cymatium suggested the scallops are subdued using secreted substances. High losses in production due to recruiting predators poses a major problem to growing E. ziczac , and possibly other tropical bivalves, in intermediate suspended culture.

Evaluation of biological and economical aspects of the culture of the scallop Lyropecten (Nodipecten) nodosus in suspended and bottom culture

Abstract We examined growth and survival of scallops Lyropecten nodosus , initially measuring 40 mm in shell length, over 4.5 months of grow-out period (from mid June to late October 1997) in four types of enclosures: in sacs, cones, lantern nets suspended at 6 m in depth and in 1×1 m corrals setup at 6 m in depth on the bottom. In all four treatments, the scallops were initially placed in the enclosures at about the same density (covering about one-third of the bottom of the enclosures). Growth of the shell and somatic tissues was greatest in sacs and cones, intermediate in lantern nets and least in bottom corrals, and cumulative mortality was greater in the bottom corrals than in the three types of suspended enclosures. An analysis of the economic profitability of different culture strategies indicated that after 4.5 months of grow-out, none of the four culture methods would be economically viable for a culture industry marketing the muscle (or the muscle and gonad together). However, the industry would be viable if whole scallops in the shell were marketed. The production would be most profitable if the scallops were cultured in cones suspended in the water column, due to the rapid rates of tissue growth, high rate of survival and low equipment costs associated with using this culture method.

Influence of environmental variables and reproduction on the gonadal fatty acid profile of tropical scallop Nodipecten nodosus.

We examined the influence of the reproductive cycle and environmental variables on the gonadal fatty acid profile in the tropical scallop Nodipecten nodosus. Individuals from a natural population in north-eastern Venezuela (Caribbean Sea) were sampled monthly during one year. The gonadosomatic index (GSI) and a visual assessment of gonadic status are also reported. The environmental conditions characterized by chlorophyll a, temperature and seston concentration were measured in parallel. The highest reproductive activity, with a GSI of 13-18%, was observed from November 2003 to April 2004, and a decrease in GSI, taken as an indication of three spawning periods, was recorded in October, January and May-June. The GSI was 5-8% outside these intervals. A similar trend was observed in maturity stage frequency. Statistical analysis (MDS-ANOSIM) established two different periods; one dominated by upwelling (January to July) and the other characteristic of non-upwelling conditions (August to December). The fatty acids 16:0, 22:6n-3, 20:5n-3 and 16:1n-7 were responsible for the differences between two periods and explained 50% of the observed variance. Accordingly, during the upwelling period, fatty acids such as 22:6n-3 were positively correlated with temperature, organic seston and bivalves in the spent sexual stage and inversely related to the GSI. Furthermore, individuals in the ripe sexual stage were positively related to 20:5n-3 and 18:3n-3, whereas chlorophyll a was directly related to 18:1n-7 and 16:1n-7. In the non-upwelling period, a significant and positive correlation was obtained between fatty acids such as 20:5n-3 and 22:6n-3 and the GSI and the bivalves in the ripe sexual stage, whereas these acids were inversely correlated with the spent sexual stage. In addition, chlorophyll a was positively related to 18:1n-9 and 18:2n-6. Changes in the gonadal fatty acid profile of N. nodosus were influenced by the environmental variables (exogenous factors) during the upwelling and non-upwelling periods and by reproductions (endogenous factors).

Effects of wave action on the growth and survival of the scallops Euvola ziczac and Lyropecten nodosus in suspended culture

Abstract We examined the impact of wave induced movement on two species of scallops in suspended culture in the Golfo of Cariaco, Venezuela, by comparing growth of juveniles in cages suspended at 6.5 m in depth using two methods. In one case movement from wave action was transmitted to the cages from supporting buoys at the surface, and in the other the supporting buoys were in deeper water, just above the cages, so that the cages were only slightly affected by wave action. For the scallop Euvola ziczac , which is normally found on sandy bottoms, the suspension methods markedly affected growth. After a 31-day growout period, all measured body parameters were markedly smaller for the scallops strongly affected by wave action than for those less exposed to wave action. The differences were 27.0% for muscle mass, 28.7% for digestive gland mass, 24.6% for the mass of remaining somatic tissues, 29.4% for gonadal mass, 13.1% for shell mass and 8.4% for shell height. Survival was 72–75% for the scallops more strongly affected by wave action compared to 94–100% for those less affected by wave action. In contrast, parallel observations on Lyropecten nodosus , which is normally found on rock and coral bottoms, showed no evidence of an effect of wave action on either growth or survival. L. nodosus was probably less affected by wave action than E. ziczac because its movement in the cages was likely reduced by its byssal attachment and by its rugose and more flattened valves. For species such as E. ziczac , wave induced movement of culture enclosures should be minimized either by choosing protected sites or by using techniques that reduce the impact of waves.

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.

Influence of Environmental Factors on the Reproductive Cycle of the Eared Ark Anadara notabilis (Röding, 1798) In Northeastern Venezuela

ABSTRACT The reproductive cycle of the eared ark Anadara notabilis and its relationship with environmental factors was evaluated every 15 days between March 2004 and February 2005 at the northern part of the Peninsula de Araya, Venezuela. Environmental factors measured included temperature, salinity, chlorophyll a, and total seston, including the particulate organic matter and particulate inorganic matter fractions. Adult specimens were collected using a net drag and then randomly selected to estimate wet live biomass and dry biomass of soft body tissues. Gonad samples were processed with histological analysis to determine sex ratio, developmental stages, and variations of follicle size. Reproduction in A. nolabilis was continuous throughout the year, with spawning peaks occurring in June and October, coinciding with the lowest water temperatures. In March, September, and November 2004, specimens attained the highest dry biomass values, whereas lowest dry biomass occurred in June and October 2004. Stepwise regression analyses demonstrated that temperature and particulate organic matter values are the main modulators of reproductive events. When temperature decreased, dribble spawning was detected in this species, possibly inducing a survival strategy whereby the spawning period is extended to increase reproductive success.

Componentes bioquímicos de los tejidos de Perna perna y P. viridis (Lineo, 1758) (Bivalvia: Mytilidae), en relación al crecimiento en condiciones de cultivo suspendido

In the organisms, the variations of the biochemical composition of reproductive and somatic tissues in the growth permit to infer about its adaptative to env...

Biometric and reproductive aspects of the pen shell Atrina seminuda (Bivalvia: Pinnidae) in northeastern Venezuela

ABSTRACT The pen shell Atrina seminuda is a target for a small artisanal Caribbean fishery; however, little is known about its biology. The length frequency distribution, biometric relations and reproduction of this species were studied in northeastern Venezuela. Using transects selected from among 360 stations a population was sampled monthly by SCUBA diving. An analysis of 1748 individuals showed a shell height (SH) between 4 cm and 23.6 cm, with an average of 16.7 ± 2.5 cm. For both sexes, statistical differences in mean SH were observed (analysis of variance F (1, 1113) = 69.538; P < 0.001); organisms larger than 22 cm were females, whereas those between 8 and 10 cm were males. Log-linear regressions were estimated for shell length (SL), total weight (TW) and adductor muscle weight (MW) as a function of SH. In all cases there were statistical differences between males and females, with males presenting positive allometry and females showing isometry. Mean SH at maturity for males (8.24 cm) was lower than for females (11.88 cm), and for sexes combined was estimated at 8.71 cm. Gametogenic activity was observed throughout the year, with two main peaks of spawning (April and August/September 2008). All this information is crucial for demographic modelling and stock assessment for managing this species.