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.

Bacteria-Affecting Cephalopods

16 pages, 6 figures, 2 tables.-- This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International LicenseBacterial pathogens contribute to obtain an unsuccessful production of cephalopods. An updated overview of the knowledge of these pathogens must be a valuable tool to improve their aquarium maintenance and aquaculture. The present work provides a description of the main bacterial pathogens associated with larval stages of cultured Octopus vulgaris, and juvenile and adults of several cephalopods. Vibrio species, reported with ability to cause vibriosis in aquaculture, are the main bacteria associated with skin lesions in adults. Different species of Pseudomonas and Aeromonas, among others, have also been detected. Furthermore, gram-positive bacteria such as Bacillus have been also described. Among them, V. alginolyticus, V. carchariae, V. parahaemolyticus, V. splendidus and V. lentus have also been isolated from sterile organs or fluids of animals and their potential as invaders proved. However, only V. alginolyticus or V. lentus has the ability to cause lesions, and, in addition, the last one is proved as the causative agent of death in octopuses. Other organs such as eyes of squids are also colonized by Vibrio species or Micrococcus sp., and recently Photobacterium swingsii and Lactococcus garvieae have been reported associated with a retrobulbar lesion in octopus. Rickettsial-like organisms (RLO) are also detected in the gills of the octopus, having a detrimental effect on the respiratory gaseous exchange of the animals. Cultures of octopus paralarvae show a genetically diverse community comparable to those reported previously from other marine hatcheries. Bacteria included in the Splendidus clade is the dominant group in all conditions, except in one of them, where V. alginolyticus, V. proteolyticus or Pseudomonas fluorescens are the main detected groups. Furthermore, Shewanella or Pseudoalteromonas undina have also been identified. All this shows that pathogenic bacteria are frequent microorganisms associated with aquarium maintenance and culture of cephalopods, and special attention on maintaining a well-balanced community of microorganisms should be appliedPeer reviewe