Dalila Aldana Aranda

COCCIDIAN (APICOMPLEXA) PARASITE INFECTING STROMBUS GIGAS LINNÉ, 1758 DIGESTIVE GLAND

Abstract This study reports on a new parasite of the digestive gland of the queen conch, Strombus gigas. An intense and generalized sporozoan infection was detected during a reproductive study of S. gigas in San Andres island (Colombia). The parasite was found in the digestive gland of every sampled S. gigas, with a heavy intensity of infection (invasion of every cell) in many animals. The infection of the digestive gland began in the cryptic cells and later secretory cells were also infected, giving way to discharge of sporocysts to the stomach through the digestive gland ducts. Apicomplexa-like trophozoites were embedded in the digestive gland epithelial cells and attached to host cell wall by their conoid end. Several stages were detected: trophozoites, sporocysts, and gamonts containing macrogametes or microgametes. Given the presence of multiple stages at the same time, the entire life cycle of the parasite is assumed to occur within the same host and tissue. The taxonomic position of the parasite should be ascertained by DNA analysis.

Effects of temperature, algal food, feeding rate and density on the larval growth of the milk conch (Strombus costatus) in Mexico

Abstract Effects of temperature, algal food, feeding rate and larval density on the development and shell growth stage of conch veligers, Strombus costatus , were studied over a period of 30 days in laboratory cultures. Experiments were conducted at 24°C, 28°C, 32°C and 28 ± 2°C. After hatching, the veligers developed to metamorphosis within 26 days at 28°C, 28 days at 28 ± 2°C and 35 days at 24°C. Rearing was not successful at 32°C. Conch larvae were fed with the algae Isochrysis aff. galbana (Tahiti), Tetraselmis chuii and Isochrysis/Tetraselmis mix. The best rate of growth per day was 39.69 μm in Isochrysis/Tetraselmis mixed food. Experiments were conducted at 500, 1000, 2000, 3000, 4000, 5000 and 6000 Isochrysis aff. galbana cells larva −1 day −1 . The veligers showed an optimal growth at 3000 cells larva −1 day −1 . The conch veligers were reared at five larval densities: 100, 200, 300, 400, and 500 larvae/l, and showed an optimal growth at 100 larvae/l, while poorest growth was observed at 500 larvae/l.

Effect of algal food and feeding schedule on larval growth and survival rates of the queen conch, Strombus gigas (Mollusca, Gastropoda), in Mexico

The effect of algal diet and feeding schedules on larval growth (daily siphonal length increments) of the queen conch, Strombus gigas, was studied over a period of 20 days in laboratory culture. Experiments were conducted at 29±1°C. Conch veligers were reared at 275 larvae·l−1 in 4-litre disinfected containers. Larvae were fed Thalassiosira fluviatilis, Isochrysis aff. galbana and Tetraselmis suecica with fixed daily rations arranged in three different feeding schedules varying from low (500–10 000) to medium (1000–30 000) and high (2000–40 000) algal cells·larva−1·day−1. Larvae fed T. fluviatilis showed total mortality of larvae fed the low and high schedules. Larvae fed the low schedule of I. aff. galbana grew slower at an average rate of 23.71 μm·day−1 than those receiving the medium and high schedules with 29.97 and 30.70 μm·day−1, respectively. Nevertheless, no differences were found between feeding schedules for this same alga, when medium and high schedules were compared (Duncan=0.05). The fastest growth at an average rate of 36.92 μm·day−1 and the highest survival of 82% were found for larvae fed the high schedule of T. suecica, even when compared with the high schedule of I. aff. galbana. Results obtained showed a better nutritional value of T. suecica over the two other algal foods tested.

Observations on ingestion and digestion of unicellular algae by Strombus gigas larvae (Mollusca, Gastropoda) using epifluorescence microscopy

Abstract Epifluorescence microscopy was used to observe the ingestion and digestion of unicellular algae in gastropod larvae. Larvae started feeding 8 h after hatching. Three kinds of diet were tested during the period of this study: Isochrysis aff. galbana, Tetraselmis chuii and Isochrysis-Tetraselmis mixture. All the experiments were conducted at 29°C. It was shown that ingestion was faster with Tetraselmis than with Isochrysis. Within 10 min 43% of the larvae had ingested Tetraselmis and no larvae had ingested any Isochrysis. Within 30 min, 60% of the larvae had ingested Tetraselmis while only 25% had ingested Isochrysis. Using a scale based on the quality of fluorescence, it was possible to determine the time interval to digest a diet, which is shorter with Tetraselmis than with Isochrysis. After 8 h the digestion index reached 45% for larvae fed with Tetraselmis while it was only 28% for larvae fed with Isochrysis. Using a quantitative scale based on measurements of the fluorescent surface in each larva, it was demonstrated that the amount of diet ingested is higher with Tetraselmis than with Isochrysis. These results indicate that Tetraselmis chuii forms an adequate diet for young veligers of Strombus gigas.

Insight of EDX Analysis and EFTEM: Are Spherocrystals Located in Strombidae Digestive Gland Implied in Detoxification of Trace Metals?

Digestive tubules of Strombidae are composed by three cell types: digestive cells, vacuolated cells, and crypt cells. The last one is characterized by the presence of intracellular granules identified as spherocrystals. Such structures are known to occur in basophilic cells of gastropod digestive gland, where they are supposed to be involved in the regulation of some minerals and in detoxification. In this study, energy‐dispersive X‐ray analysis (EDX) and energy filtered transmission electron microscopy (EFTEM) were used to determine the elemental content of spherocrystals in two Strombidae, Strombus gigas and Strombus pugilis. In freshly collected individuals of both species, the following elements were detected: Ca, Fe, Mg, P, and Zn. Aluminum and Mn were also detected in S. gigas. Their presence in spherocrystals indicates that, in Strombidae, spherocrystals are involved in the regulation of minerals and essential trace metals. In order to answer the question “are spherocrystals involved in nonessential trace metals scavenging?,” artificial cadmium and lead exposure by both waterborne and dietary pathways was applied to S. pugilis. No evidence of cadmium (Cd(NO3)2) or lead (Pb(NO3)2) provided by food was found in spherocrystals. Cadmium provided in water (Cd(NO3)2 and CdCl2) causes structural modifications of the digestive gland; however, this element was not trapped in spherocrystals. These results suggest that spherocrystals are not involved in detoxification of such nonessential trace metals. Microsc. Res. Tech., 2011.

Ingestion and digestion of eight algae by Strombus gigas larvae (Mollusca, Gastropoda) studied by epifluorescence microscopy

Abstract Epifluorescence microscopy was used to observe the ingestion and digestion processes of eight algae diets in 18-day-old Strombus gigas larvae. The eight diets used were: Isochrysis aff. galbana, Tetraselmis chuii, Tetraselmis suecica, Dunaliella tertiolecta, Chlamydomonas coccoides, Thalassiosira fluviatilis, Chlorella sp. and Chaetoceros sp. Observations were made at 0.5, 1, 2, 3, 4, 5, 6, 7, 8 and 24 h after feeding. Ingestion index was faster with T. chuii, Chaetoceros sp. and Chlorella sp. than with I. aff. galbana, D. tertiolecta, C. coccoides, T. fluviatilis and T. suecica . Digestion began at the second hour, being faster with Chaetoceros sp. and Chlorella sp. and slower with D. tertiolecta and T. fluviatilis . Values of ingestion and digestion indices were specific for each alga. This research was performed to provide helpful information in selecting the best diet for each larval stage, according to culture conditions.

Occurrence of Apicomplexa-like structures in the digestive gland of Strombus gigas throughout the Caribbean.

The queen conch, Strombus gigas, is a marine resource of ecological and economical importance in the Caribbean region. Given its importance in this region, and the critical status of most populations, the reproductive biology of this species has been studied to support management decisions. It was from these studies that a generalized sporozoan infection was detected. This study describes the geographic distribution of a coccidian (Apicomplexa) parasite infecting the digestive gland of S. gigas throughout the Caribbean. The parasite was present in every location sampled. Based on histological analysis, the parasites from all locations are similar and appear to complete their life cycle within the digestive gland. The highest occurrence of the parasites was registered in samples from Puerto Rico (54 parasites per field) and Martinique (45 parasites per field). The lowest incidence was registered on the Mexican coast of Yucatan peninsula, at Alacranes and Chinchorro with 17 parasites per field. Data showed significant differences among sites (Kruskal Wallis H=106.957; p ≤ 0.05). The abundance of parasites found in the digestive ducts and in the faeces suggests the liberation of parasites to the environment. A gradual decrease in abundance was found from East to West of the Caribbean sea.

REPRODUCTIVE STRATEGIES OF THE EASTERN OYSTER CRASSOSTREA VIRGINICA (GMELIN 1791) IN TROPICAL LAGOONS OF THE MEXICAN GULF OF MEXICO

ABSTRACT The oyster fishery is 1 of the most important coastal fisheries in Mexico. Management is based on a minimum legal size of 80 mm and several seasonal bans that vary along the coast of the Gulf of Mexico. We describe the gonad development cycle of Crassostrea virginica (Gmelin 1791) along the Mexican coast of the Gulf of Mexico for 5 lagoons for the years 2000 and 2004, between latitudes 21°41′16.75″ N and 18°23′51.08″ N. Significant differences in duration and intensity were observed among reproductive stages associated with different environmental conditions. Gametogenesis and mature stages correlated positively with temperature and total chlorophyll, respectively. Spawning correlated negatively with salinity in both years. Maturity correlated positively with total chlorophyll levels. The reproductive stages varied from seasonal, a few months, to continuous throughout the year. Recovery, expressed as the number of organisms in postspawning and resting stages, was fast for populations that presented constant gametogenesis and spawning, with less than 50% of the population in postspawning and resting stages. Environmental fluctuations in total chlorophyll are the regulating factors for gametogenic activity, rather than latitudinal temperature variations. This makes monitoring environmental conditions in the lagoons or gonad development a necessity to predict reproduction and recruitment for proper management of the oyster resource.

Effects of photoperiod on development, growth and survival of larvae of the fighting conch Strombus pugilis in the laboratory

Abstract Fighting conch, Strombus pugilis , larvae were reared from hatching to settlement under three photoperiods, with light phases of 0 light (0 L), 12 light (12 L) and 24 light (24 L) per day to test their effect on development, growth and survival. Proboscis appeared at 21 days in different percentages for three photoperiods: 30% for larvae under 0 L, 50% for larvae under 12 L and 54% for larvae under 24 L. For the three photoperiods the veligers were competent for metamorphosis between 27 to 31 days. Under 0 L conditions frequency of metamorphosis was lower. The settlement period was similar in 24 L and 12 L conditions, but the duration was significantly longer below 0 L conditions. Continuous light had a negative effect on survival, while continuous darkness was advantageous. The percentage of survival at settlement was significantly lower under 24 L (13%) and 12 L (22%) conditions, while 0 L was 44%. Larval growth averaged 22.56, 23.36 and 29.60 μm dia. −1 below 0 L, 12 L and 24 L conditions, respectively. The siphonal length at settlement was longer for larvae under 24 L than that below 0 L and 12 L conditions.

GONAD DEVELOPMENT AND REPRODUCTIVE PATTERN OF THE FIGHTING CONCH STROMBUS PUGILIS (LINEÉ, 1758) (GASTROPODA, PROSOBRANCHIA) FROM CAMPECHE, MEXICO

Abstract The processes of gonad development through a year are analyzed for Strombus pugilis from Seybaplaya, Campeche. During gametogenesis second order oocytes appear close to the wall of the follicles, with a diameter 90–250 μm. The cytoplasm is granular, the nucleus is located on the periphery, with a diameter of 15–35 μm, a nucleolus 7–8 μm. Spermatozoids have an acrosome of 5–7 μm, shaped like a coma. In females gametogenesis was registered in two pulses, with 2 peaks of 60%, February to June and September to October. Mature females were found during the 8 months of sampling with peaks during May and August (80%). Spawning was discontinuous, suggesting storage of mature gametes for the right time to spawn. In males gametogenesis was present in a low percentage from March to October, with a maximum of 20%. Maturity was present on just a 10% during July, with constant spawn through the year. Copula has been observed only during egg laying seasons; males seem to keep mature sperms in the prostate gland. Strombus pugilis from the coasts of Campeche presented a fast gonad recovery for males, requiring longer for females. Having missed most of the autumn and early winter months leaves a big gap on the processes of gonad recovery and early gametogenesis. Apparently there is no correlation between salinity, temperature and the reproductive cycle, but this population has the potential for reproducing through the year.