SummaryThe occurrence of the parasitic marine leech Stibarobdella moorei (Oka, 1910) (Hirudinea: Piscicolidae) along the northwest Mexican Pacifi c coast is described for the fi rst time. This ectoparasite was collected from the skin of the Octopus bimaculatus (Verril, 1983) (Mollusca: Octopodidae). Stibarobdella loricata (Hardig, 1924) is synonymized with S. moorei as this species resembles other species of the genus based on tubercle patterns and the presence of papillae and a marginal fringe on the oral sucker. The present fi nding throws new light on the biodiversity and host preference of the ectoparasite and suggests a successful migration to unusual host. The coast of the Pacifi c Ocean, particularly in the Bay of Los Angeles, Baja California, Mexico is a new geographical distribution area for S. moorei, and O. bimaculatus is a new host reported for this leech. The morphology of this ectoparasite is briefl y described.

Astaxanthin is an essential micronutrient that regulates shrimp physiology, acting as a free radical scavenger, increasing stress resistance, and enhancing the immune response, improving growth and survival in farm-raised organisms. Despite this, accumulation of astaxanthin has not been evaluated regarding rearing conditions of shrimp. Thus, this study aimed to assess the effect of rearing conditions (extensive vs. hyperintensive) in the accumulation of astaxanthin in tissues of shrimp Penaeus vannamei, using wild juveniles as a reference of the levels of astaxanthin present in the natural environment. The main oxycarotenoid found was astaxanthin, which was mostly accumulated in hepatopancreas (>90%) in esterified form, while mostly free astaxanthin was found in exoskeleton and muscle (<60%). Comparing wild and reared shrimp, the content of esterified astaxanthin was significantly higher in the hepatopancreas of shrimp reared under extensive conditions (191.45 ± 23.08 μg g -1 ) followed by wild shrimp (144.08 ± 13.92 μg g -1 ), while low values (3 ± 1 μg g -1 ) were found in shrimp reared under hyper-intensive conditions. Astaxanthin levels found in farm-raised shrimp were not explained by commercial feeds, since no astaxanthin (only traces of its chemical precursor β-carotene), was found in the six different commercial feeds analyzed for rearing shrimp. Thus, the results may be explained by primary productivity (i.e., phytoplankton) that is consumed as natural food by shrimp in the ponds of farming systems, or by the effect of specific rearing conditions on the microbiota associated with carotenogenesis in the gut of shrimp. In any case, commercial feeds should fulfill all nutritional requirements for shrimp, particularly under stressful conditions as it occurs in hyper-intensive farming.

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The high mortalities registered in the larval stage during octopus culturing are mainly due to nutritional deficiencies of the food provided. To understand the cause of this problem, we studied the ontogenetic development of the digestive system of Octopus bimaculatus paralarvae. An egg batch was obtained from a gravid female collected in the Bay of Los Angeles, Baja California, Mexico, and it was incubated in the laboratory during the summer of 2011. We observed that the formation of the digestive system began at 33 days post-laying (DPL). The newly hatched paralarvae had already formed the organs involved in food ingestion and digestion, although it was not possible to know accurately their degree of maturity. The present research constitutes the first description at the histological level of the ontogenic development of the digestive system of the O. bimaculatus paralarvae. This serves as a basis for future studies of the digestive physiology of this species.