Mature calico scallops, Argopecten gibbus, collected from the grounds off Cape Kennedy, Florida, were induced to spawn in the laboratory. Fertilized eggs were reared to postlarvae in sea water of 23° C ± 2.0° C at a salinity of 35 %o. The external morphology of eggs and developing larval stages are described

Costello, T. J.

DuPuy, John L.

Hudson, J.Harold

Rivkin, Samuel

English

College of William & Mary: W&M Publish

W&M ScholarWorks VIMS Articles Virginia Institute of Marine Science 1973 Larval culture of the calico scallop, Argopecten gibbus T. J. Costello J.Harold Hudson John L. DuPuy Samuel Rivkin Follow this and additional works at: https://scholarworks.wm.edu/vimsarticles  Part of the Aquaculture and Fisheries Commons Proceedings of the National Shellfisheries Association Volume 63 - June 1973 LARVAL CULTURE OF THE CALICO SCALLOP, ARGOPECTEN GIBBUS 1 , 1 T. J. Costello, J. Harold Hudson, John L. Dupuy and Samuel Rivkin NATIONAL MARINE FISHERIES SERVICE SOUTHEAST FISHERIES CENTER MIAMI, FLORIDA AND VIRGINIA INSTITUTE OF MARINE SCIENCE GLOUCESTER POINT, VIRGINIA ABSTRACT Mature calico scallops, Argopecten gibbus, collected from the grounds off Cape Kennedy, Florida, were induced to spawn in the laboratory. Fertilized eggs were reared to postlarvae in sea water of 23° C ± 2.0° C at a salinity of 35 %o. The external mor-phology of eggs and developing larval stages are described. INTRODUCTION The calico scallop, Argopecten gibbus (Linne), (Fig. 1)3 is a commercially valuable shellfish which supports a developing fishery off the southeastern coast of the United States and in the Gulf of Mexico. Large concentrations of this benthic marine pele-cypod occur on the continental shelf in the area of Cape Kennedy, Florida, in depths from 9-74 m (Drummond, 1969). Concentrations also occur south of Cape Hatteras off North Carolina in depths from ca. 13 m (Bullis and Thompson, 1965) to at least 94 m (Cummins, Rivers and Struhsaker, 1962). The general distribution of this organism is given by Allen and Costello (1972). The National Marine Fisheries Service (NMFS) 1 Contribution No. 225, Southeast Fisheries Center, National Marine Fisheries Service, NOAA, Miami, FL 33149. 2 Contribution No. 4 78, Virginia Institute of Marine Science, Gloucester Point, VA 23062. 3 Two terms are used in this paper to define shell dimensions. They are: (1) Length (L), a straight line measurement of the greatest distance between the anterior and the posterior shell margins; (2) Width (W), a straight line measurement of the greatest distance between the umbo and the ventral shell margin. Several authors use the term "height" for the dimension we define as width. 72 initiated a life history study of calico scallops in 1969. A portion of the study was concerned with the early life history of this mollusk. The purposes of this paper are: (1) to present illustrations of the gross morphology and time sequence of larval development so these stages may be readily identified in plankton samples, and (2) to make available procedures for the mass culturing of this species. Previous works on larval development of mollusks of the genus Argopecten 4 are by Belding (1910), Gutsell (1930) and Sastry (1965). These papers deal with a closely related species, the bay scallop, Argo• pecten irradians. MATERIALS AND METHODS Techniques to induce spawning and rear molluscan larvae suggested by Loosanoff and Davis (1963) were modified at the Virginia Institute of Marine Science (VIMS) in rearing calico scallop larvae. Mature calico scallops (shell width 55 - 65 mm) were collected by otter trawl from the grounds off Cape Kennedy, Florida_. They were transported to the NMFS Labora-tory in Miami, Florida, in insulated containers of aerated sea water maintained at 20 - 23° C. At the laboratory, scallops were held on water tables and/or troughs of running sea water. Subsequently, a portion 4 Waller (1969) rejected the generic name Aequipec-ten and suggested Argopecten, the name currently in use. LARVAL CULTURE OF SCALLOPS FIG. 1. The right valve of a mature calico scallop, Argopecten gibbus - shell width 56 mm. of these mature scallops was air-shipped to VIMS at Gloucester Point, Virginia, where spawning and larval rearing to setting were accomplished. AU culture techniques and most of the mor-phology were described from specimens, photomicro-gra ph s a nd information obtained from induced spawning and larval rearing at VIMS. Induction of Spawning Ovarian color is a reliable index of sexual maturity in calico scallops (Miller, Hudson, Allen and Costello, 1972).5 Before we attempted to induce spawning, sc all o ps were selected that showed orange-red (" ripe") ovarian color. The ovarian color was easily observed as the scallops gaped in the troughs of run-ning sea water. Preliminary observations indicated that induced spawning in ripe calico scallops is easily achieved. We induced spawning several times in less than one hour by raising the water temperature from ca. 20 . 25° C. To trigger spawning, in addition to raising the water temperature, it was occasionally necessary to strip gametes from one mature calico scallop specimen and, with a pipette, introduce them gently into the water containing gaping scallops. Calico scallops are hermaphrodites. Sperm cells are 5 Miller, G. C. , J. H. Hudson , D. M. Allen, and T. J. Costello. 1972. Ovarian color changes in calico scal-lops, Argopecten gibbus. Unpublished manuscript filed at the National Marine Fisheries Service, South-east Fisheries Center, Miami Laboratory, Miami, Fla. 73 usually extruded first when spawning is induced in the laboratory. After sperm cells have been dis-charged for 30 min to an hour, discharge of eggs begins. Once spawning begins, it may continue for several hours. When techniques to induce spawning were estab-lished, 10 ripe scallops were selected. Their shells were carefully scrubbed to remove a variety of en-crusting invertebrates which are frequent ly affixed to the outer shell (Wells, Wells and Gray, 1964). If these fo u Ii ng organisms, e.g. , the serpulid polychaete, Pomatoceros caeruleus, are not removed, they may spawn when spawning is induced in the scallops and contaminate the larval culture. After cleaning, the scallops were placed, one to a dish, in 3" x5"x9" Pyrex glass containers, each % filled with filtered 20° C sea water at a salinity of 32.1 ~.. . The containers were then placed on a water table. A black cloth was placed between the glass con-tainers and the table top to aid in observing when spawn was first extruded. Temperatures in the dishes containing scallops were raised from 20 - 25°C by flowing warm tap water around them. In two of the dishes, sperm cells stripped from another mature calico scallop were introduced with a pipet te. The scallops in these two dishes began to spawn 78 min after the water temperature reached 25°C. Six addi-tional scallops spawned at varicus intervals in the next hour. When the water in each dish became clouded (opaque) with suspended sperm, the scallop was re-moved and placed in a clean dish of 25° C fil tered sea water. This procedure was continued until the scallop began to discharge only eggs. The scallop was then placed in a clean dish of 25° C filtered sea water where it was kept until spawning was completed. Dishes containing mixed sperm and eggs were dis-carded. Since the eight scallops induced to spawn began extruding sperm and then eggs at various times over ca. a 2-hr period, we had available, simultaneously, dishes containing freshly spawned, unmixed suspen-sions of sperm cells, and freshly spawned, unmixed suspensions of eggs. A light suspension of sperm (35 cc) was added to each of the dishes containing eggs, and the mixtures were gently agitated. Following fertilization, the eggs were washed in a stainless steel screen (152 µ openings) to remove debris that ac-companies spawning. We followed the washing pro-cedure described by Loosanoff and Davis (1963). After the fertilized eggs were washed, they were added to a container of fil tered sea water and the number of eggs per unit of sea water was determined with a Sedgwick-Rafter cell. A sufficient quantity of 74 T.J. COSTELLO, J.H. HUDSON, J.R. DUPUY ANDS. RIVKIN the washed egg suspension was added to a 20-liter container6 of filtered sea water to provide 25 eggs/ml. This concentration was reduced to ca. 10 larvae/ml at the straight-hinge stage. Temperature in the culture was maintained at 23° C ± 2.0° C throughout larval development. To simu-late conditions in the calico scallop's natural offshore spawning area, salinity was adjusted to 35 %0 imme-diately after fertilization and held at this concentra-tion. The culture was not aerated, and no illumina-tion was provided. Water was changed every other day by straining the entire 20 liters through a stain-less steel screen. A screen with mesh openings of 50µ was used initially; larger openings were used as the larvae increased in size. Larvae retained on the screens were returned to clean 20-liter containers of filtered sea water. Following the first two water changes, 0.2· cc of "twin biotic" (a mixture of streptomycin and' penicillin) was added per liter of culture to retard bacterial growth. Feeding of the larvae was initiated 30 hr after fertilization . Unialgal cultures of Mono-chrysis lutheri were fed in quantities sufficient to provide, initially, concentrations of ca. 60,000 cells/ml. As the larvae grew, adjustments to concen-trations of food were made to quantities where observations showed complete utilization. EMBRYONIC DEVELOPMENT Embryonic development of A. gibbus is similar to that described by Sastry (1965) for A. irradians. A detailed study of early cleavage was not made; there-fore, the times that are reported for early embryonic development are approximations based on the most 6 Plastic garbage can • • FIG. 2. Argopecten gibbus eggs ca. 35 min after spawning. Note irregular shape of most eggs. 0 I ' I . a - 60 µ ------i & d . . g Fl G. 3. Embryonic development of Argopecten gibbus: a) unfertilized eggs; b & c) zygotes 40-60 min after fertilization showing polar bodies; d) cell divi-sion ca. 100 min after fertilization; e) a ciliated trochophore 24 hr after fertilization. typical stage represented in the culture samples ob-served. Developing zygotes from a single spawning showed considerable disparity in rates of develop-ment during the first 24 - 36 hr. Newly spawned eggs of A. gibbus were asymmetrical (Fig. 2), though observations of A. irradians eggs observed after spawning also appeared similarly asymmetrical. Unfertilized eggs, measured with an ocular micro-meter, averaged 60µ in diameter (Fig. 3a). Approxi-mately 40 min after fertilization, two polar bodies formed as the zy gote gradually modified to form a polar lobe (Figs. 3b and 3c). In most cultures discern-ible cleavage began 70 min after fertili zation. As in the embryonic development of many other molluscs, unequal blastomeres were noted in all early cleavages, and micromeres proceeded with more rapid division than macromeres during the first 8 hr of develop-ment. Figure 3d depicts typical cell division 100 min after fertilization. Active ciliated trochophores were observed 24 hr after fertilization (Fig. 3e). Shell secretion began during the early trochophore stage. The shell gradually enveloped the body and an active straight-hinge veliger was formed before the larvae were 48 hr old. Larval Culture Under our laboratory conditions, the larval period of the calico scallop was 16 days. Figure 4 is a com-posite made from photomicrographs taken every 24 hr. The larvae, items B through J in Figure 4, repre-LARVAL CULTURE OF SCALLOPS • • A 70 II - 80 fl 189 L Xl70W B • .e 21 0 L X I 80 W 9 0 L X 69 W C 2 I O L X I 90 W I I 2 L X I 00 W D 12 0 L X I 08 W 2 5 0 L X 208 W ~>~) E -.. ...--/.~ ·-· { ~-·,. (,p, J ~ : .I 140 L X 130 W 250 L X 208 W FIG. 4. Composite photomicrograph of larval Argo-pecten gibbus. Age in days: a) 1; b) 2; c) 4; d) 5; e) 7; f) 9; g) 11; h) 13; i) 15; j) 16. L ength x width dimen-sions are given in microns. sent the average sizes for each time stage obtained by measurement of 25 larvae from several photomicro-graphs of each 24-hr period. The early straight-hinge larvae appeared to be chopped o ff at one poin t alo ng the hinge line. The umbo appeared at about 140 µ, rounded and poorly defined. It remained incon-spicuous throughout larval developmen t. Figures 5 and 6 show typical morphological features in the lat-ter stages of larval development and just prior to se t-ting. Chanley and Andrews (1971) made effec tive use of hinge line shapes in describing 23 species of bivalve larvae. The hinge line shape o f t he calico scallop lar-vae (Fig. 7) is distinctive but very similar to A . irradians. The too thed area is comprised of t hree taxodont teeth at each end of the hinge line. The central hinge area is undifferentiated. Other identify-ing characteristics of calico scallop larvae are their 75 FIG. 5. Photomicrograph of live 12-day-old larvae of Argopecten gibbus length 210 µ. pale color and development of an inconspicuous eye-spol when the larvae reach a length of ca. 250 µ. SUMMARY Calico scallops, A. gibbus, have been induced to spawn in the laboratory and the larvae have been reared to setting. Development, on the basis of ex-ternal morphology, is quite similar to that recorded for a closely related form, A. irradians (Sastry, 1965). FIG. 6. Photomicrograph of live 16-day-old larvae with foot extended, showing anatomical relationship and early structure of gill and foot. 76 T.J. COSTELLO, J.H. HUDSON, J.R. DUPUY AND S. RIVKIN FIG. 7. Dorsal view of hinge of the larval Argopecten gibbus. The major difference is that A. g1bbus has a much larger pediveliger or newly set larvae which ranges in length from 235-270 µ . The difference is significant when compared to the bay scallop, A. irradians, which sets at a length of from 170-190 µ.. ACKNOWLEDGMENTS This work was supported in part by the NOAA Office of Sea Grant, Department of Commerce, under Gran t No. 1-36032. We express our sincere thanks to Dr. Kenneth Chew, Mr. Robert Work, and Mr. William Shaw for their very helpful editorial sug-gestions. LITERATURE CITED Allen, D. M. and T. J. Costello. 1972. The calico scal-lop, Argopecten gibbus. NOAA Tech. Rep. NMFS SSRF-656, 19 p. Belding, D. L. 1910. A report upon the scallop fish-ery of Massachusetts, including the habits, life history of Peclen irradians, its rate of growth , and other facts of economic value. Wright and Potte r Printing Co., Boston, 150 p. Bullis, H. R., Jr. and J. R. Thompson. 1965. Col-lections by the exploratory fishing vessels Oregon, Silver Bay, Combat, and Pelican made during 1956-1960 in the southwestern North Atlan tic. U. S. Fish Wild!. Serv., Spec. Sci. Rep. Fish. 510, 130 p. Chanley, P. and J. D. Andrews. 1971. Aids for identi-fication of bivalve larvae of Virginia. Malacologia, 11: 45-119. Cummins, R., Jr., J. B. Rivers and P. J. Struhsaker. 1962. Exploratory fishing off the coast of North Carolina, September 1959 · July 1960. Commer. Fish. Rev. 24(1): 1-9. Drummond, S. B. 1969. Explorations for calico scal-lo p, Pecten gibbus, in the area off Cape Kennedy, Florida, 1960-66. Fish. Ind. Res. 5: 85-101. Gutsell , J. S. 1930. Natural history of the bay scallop. Bull. U.S. Bur. Fish. 46: 569-632. Loosanoff, V. L. and H. C. Davis. 1963. Rearing of bivalve mollusks. Adv. Mar. Biol. 1: 1-136. Sastry, A. N. 1965. The development and external morphology of pelagic larval and post-larval stages of the bay scallop, Aequipecten irradians concen-lricus Say, reared in the laboratory. Bull. Mar. Sci. 15: 417-435. Waller, T. R. 1969. The evaluation of the Argopecten gibbus stock (Mollusca: Bivalvia), with emphasis o n the Tertiary and Quaternary species of the eastern North America. Paleontol. Soc. Mem. 3, 125 p. Also J. Paleont. 43 (5, Suppl.) Wells, H. W., M. J. Wells and I. E. Gray. 1964. The calico scallop community in North Carolina. Bull. Mar. Sci. 14: 561-593. 

Larval culture of the calico scallop, Argopecten gibbus

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Larval culture of the calico scallop, Argopecten gibbus

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