Length and age structure in commercial catch samples of the pismo clam Tivela stultorum (Mawe, 1823), from Playa San Ramon, B.C., Mexico

Age was determined in 1,368 pismo clams (Tivela stultorum, Mawe, 1823) by growth ring analysis, in commercial catch samples collected from July 1978 to February 1983. Approximately 25 age classes were present between 1978 and 1980, divided into two modal groups (younger and older than 21 years), suggesting the occurrence of wide fluctuations in abundance. During the study period a general decreasing trend was observed in average length (from 12.2 cm in 1978 to 10.9 cm in 1983) and age (from 24.9 years in 1978 to 17.9 years in 1983), probably as a result of overexploitation

Effects of and factors associated with umbilical hernias in a swine herd

abstract: Factors associated with umbilical hernias were evaluated in a 320-sow, farrow-to-finish herd. Health, production, and treatment records for a cohort of 2958 pigs were used to determine whether umbilical infection and sire of the pig increased the risk of herniation. Although herniation was infrequent (1.5%), there was evidence of increased risk in offspring of 2 boars (1 American Spotted and 1 Duroc) and in pigs that had clinical or gross pathological evidence of umbilical lesions. For pigs in this study, umbilical herniation was not fatal, despite lack of treatment, and affected pigs had no evidence of reduced growth rate after weaning up to about 45 kg. Results supported existing genetic and infectious hypotheses about causes of umbilical hernias and provided additional data to aid decision making about alternative treatment and control strategies

Effect of darkness on the early postlarval development of Haliotis corrugata abalone fed different diatom densities

Four-day-old postlarvae of the abalone Haliotis corrugata were exposed to different diatom densities (Navicula incerta, 0 to 8000 cells mm–2) under two illumination conditions: constant light (19–21 µmol quanta m–2 s–1) and darkness. The effect of these two factors on postlarval grazing rate, survival, and growth was evaluated. The experiment was conducted for 14 days in 10-mL sterile wells following a split-plot experimental design with three replicates per treatment. The highest grazing rate was observed in the 2000 cells mm–2 density treatment and it was higher in darkness (196 ± 67 cells pl–1 h–1) than in constant light (139 ± 36 cells pl–1 h–1). Mean survival was also higher in darkness (59%) than under constant light (44%), as was mean growth rate (20 and 14 µm d–1, respectively). Growth rate at the end of the experimental period tended to decrease with the increase in diatom density. Higher grazing and growth rates in darkness reinforce the hypothesis that the nocturnal habits of abalone develop soon after metamorphosis and not at juvenile stages as usually considered.

International workshop on marine invertebrates: Future directions of multidisciplinary research in larviculture

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