BULLETIN OF MARINE SCIENCE, 64(2): 201–208, 1999 DEVELOPMENT, GROWTH AND SURVIVAL OF LARVAE OF THE FIGHTING CONCH STROMBUS PUGILIS L. (MOLLUSCA, GASTROPODA) IN THE LABORATORY Nancy Brito Manzano, Dalila Aldana Aranda and Erick Baqueiro Cárdenas ABSTRACT The development, growth and survival of Strombus pugilis (Linné, 1758) larvae were studied over a period of 31 d in laboratory culture. Experiments were conducted at 29°± 1°C. Veligers were reared at 200 larvae L−1 in 4-L containers. Larvae were fed with the algae Tetraselmis suecica at 1000 cells L−1. S. pugilis larvae have 1.5 whorls at hatching, the veligers are competent for metamorphosis in 30 to 31 d. Nineteen development char- acteristics are described from hatching to settlement. Based on chronological appearance and dissapearance of the characteristics, seven development stages are proposed. Aver- age size at hatching was 212 ± 8.03 µm. Larval growth averaged 26.16 µm d−1. Mean shell length of 997 ± 18.12 µm and maximum shell length of 1022 µm were reached 31 d after hatching. Survival ranged from 20.50 to 22. 25% for three replicates. Results of this study are compared with descriptions of larvae from the literature of the four most abun- dant Strombus spp. Further studies are needed before the feasibility of S. pugilis larvae culture can be adequately ascertained. The fighting conch, Strombus pugilis (Linné, 1758), is one of six species of conchs distributed throughout the Caribbean inshore waters on sandy bottoms. (Berg, 1976; Brownell and Stevely, 1981; Berg, et al., 1983). Around the Yucatán Peninsula, Mexico, conchs are an important economic resource to the inhabitants of the region. Total conch production in 1983 reached a maximum of 1250 mt in the Yucatán, which a generated of direct income to fisherman of approximately US$200,000. However, overfishing and lack of regulations have wiped out some populations, in particular in the state of Yucatán where a permanent ban on conch harvesting was set since 1988 (Baqueiro, 1997). Figure 1 shows the decline of conch production for the state of Yucatán. Therefore, it is impor- tant to develop aquaculture techniques to enhance production through private and public mariculture. Even though all six species are exploited, research has only been done on queen conch, S. gigas and the milk conch, S. costatus. Papers on culture of fighting conch are limited and, according to our knowledge only two papers exist: Brownell (1977) and Bradshaw-Hawkins (1982). The objective of this study was to determine the feasibility of rearing larval S. pugilis in the laboratory and to describe the development process to permit further studies on the aquaculture potential of the species. MATERIALS AND METHODS Three fertilized egg masses used for the larval culture experiment were collected in August at Seyba Playa, Yucatán Peninsula, Mexico (20°45'N and 91°45'W), from a depth of about 3 m. The egg mass taken from under a conch female to ensure species identity and egg freshness was cleaned with filtered and UV sterilized seawater. The cleaned egg mass was placed over a 300 µm mesh and kept immersed in a 25-L aquarium with seawater filtered through 10 and 2 µm cotton filters and 201 202 BULLETIN OF MARINE SCIENCE, VOL. 64, NO. 2, 1999 Figure 1. Yearly conch production for the state of Yucatán, Mexico for the period 1980-1988, when a permanent ban on fishing was imposed. UV-sterilized. Egg mass and larvae were maintained at 29° ± 1°C and the water was changed every 24 h. EGG MASS AND LARVAL CULTURE.—The number of S. pugilis eggs per egg mass was estimated by separately hatching three egg masses in 25 L of seawater. Egg strand and capsule diameters were projected onto a TV monitor using a video camera attached to a dissecting microscope (5×), and were measured using a JV6000T video micrometer. The hatched veligers were stirred and three 10 ml aliquots were counted. Additional egg mass data were obtained from Robertson (1959), Randall, (1964), Bradshaw-Hawkins (1982) and Davis et al., (1993). Veliger larvae were reared according to the methods described by Davis and Hesse (1983) for S. gigas, since the culture conditions for S. pugilis are poorly known. Three experimental cultures were set up in 4-L containers with a density of 200 larvae L−1. Larvae were fed algae (Tetraselmis suecica) at a concentration of 1000 cells ml−1 d−1. This ration was determined according to García Santaella and Aldana Aranda (1994). Every 2 d, 30 larvae were collected at random from each replicate for the observation of growth and development. LARVAL DEVELOPMENT.— Larval development was observed by examination of velum: number of lobes and disappearance of velar lobes, number of shell whorls, presence of proboscis and radula, foot and mantle pigmentation, tentacles, larval heart, eyes stalks, adult operculum claw, swim crawl behavior and settlement. Developmental characteristics were numbered chronologically as they appeared and then calculating the incidence percentage in the developing larvae. Developmental stages are proposed using the moment of first appearance of one or several characteristics. LARVAL GROWTH AND SURVIVAL.—Growth was measured using a compound microscope with a calibrated ocular micrometer to the nearest 0.10 µm. Growth rates were calculated according to García Santaella and Aldana Aranda (1994) as the average growth rate in µm d−1 = (average shell length at the end of the experiment minus the average shell length at the beginning divided by total growth period in days. Survival rates were calculated using the number of living larvae at the beginning of the experi- ment and end of the experiment. RESULTS EGG MASS.—Egg strand diameter was 508 µm, the average number of eggs per mass was 220,000, the number of eggs per coil of the strand was three, and egg-capsule size BRITO MANZANO ET AL.: LARVAE OF THE FIGHTING CONCH STROMBUS PUGILIS 203 .tnemelttesotgnihctahmorfscitsiretcarahctnempolevedlavralfonoitpircseD.1elbaT scitsiretcarahC Ddscitsiretcarahctnempoleve Daysol rebmun 1sT1wolobesand1.5whorl 2sF5ourlobesand2.0whorl 3sF8ourlobesand2.5whorl 4sF1ourlobesand3.0whorl1 5sA1dultheartappear 1 6mT1entaclesstalksbegintofor1 7sF5ourlobesand3.5whorl1 8sS5ixlobesand3.5whorl1 9sM5igrationofeyesupthetentaclesstalksbegin1 1e0P5igmentationofthemantl1 1t1P7igmentationofthefoo1 1s2S8ixlobesand4.0whorl1 1s3P0roboscisappear 2 1s4R0adulaappear 2 1s5S3ixlobesand4.5whorl2 1s6F3unctionofproboscisingrazingofalgaebegin2 1e7T3heoperculumadultclawvisibl2 1s8F7unctionoffootonthesubstratebegin2 1d9Settlement(dissapearanceofvelarlobes,outwar27 migrationofeyesandswim-crawlbehavior) was 190 µm. The eggs hatched 98 h after spawning at 29 ± 1°C. Average size shell length at hatching was 212 ± 8.03 µm. DEVELOPMENT.—Newly hatched larvae have a velum with two lobes and a shell with one and a half whorls. These characteristics presented at hatching and larvae evolution are shown in Table 1, in which 19 characteristics are described for the full larval develop- ment. After 31 d the larvae are competent for metamorphosis having velum with six lobes, shell with 4 or 4.5 whorls, fully developed adult heart, eyes on top of stalks, a foot with a dark green pigmentation, and the proboscis and radula are fully developed. Table 2 shows the incidence percentages of the 19 characteristics recorded during de- velopment of the larvae from hatching to settlement. Of these characteristics two sets were identified: larval maturation and metamorphic processes. Larval maturation set con- sists of characteristics 1, 2, 3, 4, 7, 8, 12 and 15, which relate to the evolution of velum and shell. These characteristics are replaced one by another during development; while the rest of the characters (5, 6, 9, 10, 11, 13, 14, 16, 17, 18 and 19) are additive characters, making up the metamorphic process that starts the development of adult organs. These 19 characteristics are used to identify seven development stages from hatching to settlement. A stage was defined on first appearance of one or several development characteristics. Stage I, development characteristic 1; stage II, development characteris- tic 2; stage III, development characteristic 3; stage IV, development characteristics 4, 5 and 6; stage V, development characteristics 5, 6, 7, 8, 9, 10 and 11; stage VI, development characteristics 5, 6 and 9 to 17; stage VII, development characteristics 5, 6, and 9 to 19. GROWTH AND SURVIVAL.—Table 3, shows growth rate, survival and linear regression equations for the three replicates. An analysis of variance (ANOVA) was carried out on 204 BULLETIN OF MARINE SCIENCE, VOL. 64, NO. 2, 1999 13 1001 056608 020479 1001001 2957979 0526070808 0325664708 0 0709090900 772 30586478708 1001001001001001 1001001001001001 613939871433 .syad13ot1morfscitsiretcarahctnempolevedneeteninehtgnitneserpeavralfoegatnecreP.2elbaT 1437335666809001 l o s y a 142442697687809001 2654768094900 20545 70503 D 0 30406376900 50657484900 0 1315171911232527292 1001 0 1 0 1001 0 135791 0 1001 c i t s i r 71 81 91 41 61 31 1 0 93 60 21 51 87 20 30 40 73 e t 13 12 c a r ssecorpcihpromate a h Cd noitarutamlavra ste M5 L1 Ss BRITO MANZANO ET AL.: LARVAE OF THE FIGHTING CONCH STROMBUS PUGILIS 205 .3elbaT siligupsubmortS htiwdef,snoitauqenoissergerraenildnalavivrus,setarhtworgeavral aciceussimlesarteT lmsllec000,1fonoitartnecnocata −1 d−1 °92taderaerdna ± .C°1 Rdsetacilpe Growthrateµm−1Ssurvival%Linearregressionequation a0227.2Y2.=228.07±25.72x;r2=0.994 b3255.2Y0.=203.27±33.45x;r2=0.990 c2266.2Y0.=210.42±27.93x;r2=0.994 the slopes obtained for growth rate for three replicates, this showed no significant differ- ence (P < 0.05). A linear fit gave the highest correlation coefficient. Growth rates ranged from 25.3–27.0 µm d−1 and the larvae reached a mean shell length of 997 ± 18.12 µm after 31 d. Survival rate 31 d after hatching was 20.5–22.2% for the three replicates with average of 21.1%. DISCUSSION Table 4 shows literature data for comparison of egg mass characteristics in different Strombus species. S. pugilis larvae have 1.5 whorls at hatching which is the same as S. gigas and S. costatus (Davis et al., 1993).