Immune response of the Almaco jack (Seriola rivoliana) against the infestation with Neobenedenia sp. in three cultivated temperatures.

The Almaco jack (Seriola rivoliana) is a marine fish maintained in mariculture systems and frequently infested by monogenean parasites like Neobenedenia sp. Severe infestations can lead to high mortalities and economic losses for farmers. This study evaluated the effects of temperature on the immune response on Almaco jack infested with Neobenedenia sp. We exposed infested fishes at temperatures of 20 °C, 24 °C, and 30 °C for 20 days and took samples of different tissues at the beginning of the experiment, and after 3 and 20 days. The tissues considered were the skin, thymus, cephalic kidney, and spleen to evaluate the relative gene expression of different genes: Hsp70, IgM, IL-1ß, IL-10, and MyD88. Our results showed an increase in IL-1ß gene expression in the skin after 20 days of infestation but no significant effect of temperature on gene expression, despite increases in infestation rates with temperature. Therefore, relative genetic expression was controlled by the number of parasites and the days post-infestation. These results show that the parasite infestation induced a local response in the skin, but that temperature has an indirect effect on the immune system of Almaco jack.

Effects of temperature on the life cycle of Neobenedenia sp. (Monogenea: Capsalidae) from Seriola rivoliana (Almaco jack) in Bahía de La Paz, BCS Mexico.

Seriola rivoliana cultivated in Mexico are infected by Neobenedenia sp. (Monogenea: Capsalidae), resulting in dermal ulceration and subsequent bacterial invasion that can cause fish death. This study assesses the effects of temperature over hatching success, oncomiracidia longevity, and infection success. The experimental design consisted of culturing the parasite at temperatures ranging between 16 and 32 °C. The oncomiracidia infection success, time to sexual maturity, and size at sexual maturity of Neobenedenia sp. were examined only at three temperatures (20 °C, 24 °C, and 30 °C). Experiments were conducted under controlled conditions in the laboratory. The oncomiracidia development was found to be faster at warmer temperatures (4-5 days between 24 and 30 °C) than in colder treatments (7-11 days between 18 and 20 °C). Hatching success and oncomiracidia longevity were higher at 24 °C and 26 °C. At 20 °C, 24 °C, and 30 °C, infection success was greater than 90%. Additionally, the laid eggs were observed at 9, 12, and 15 days at 30 °C, 24 °C, and 30 °C, respectively. The results of this study will allow for improving the temporal schedule of applications of treatments against Neobenedenia sp. by the function of temperatures. In conclusion, it is recommended to treat fish more frequently if the temperature in cultures is higher than 24 °C, because Neobenedenia sp. development is faster. As an alternative, the fish could be moved to deeper and cooler waters.

Early development and life cycle of Contracaecum multipapillatum s.l. from a brown pelican Pelecanus occidentalis in the Gulf of California, Mexico.

The initial developmental stages of Contracaecum multipapillatum (von Drasche, 1882) Lucker, 1941 sensu lato were studied using eggs obtained from the uteri of female nematodes (genetically identified) found in a brown pelican Pelecanus occidentalis from Bahía de La Paz (Gulf of California, Mexico). Optical microscopy revealed a smooth or slightly rough surface to the eggs. Egg dimensions were approximately 53 × 43 µm, although after the larvae had developed inside, egg size increased to 66 × 55 µm. Hatching and survival of the larvae were greater at 15°C than at 24°C, and increased salinity resulted in a slight increase in hatching but seemed to reduce survival at 24°C, but not at 15°C. The recently hatched larvae measured 261 × 16 µm within their sheath. When placed in culture medium, the larvae grew within their sheath, and a small percentage (~2%) exsheathed completely (314 × 19 µm). The larvae continued to grow and develop once they had exsheathed, attaining mean dimensions of 333 × 22 µm. Although they did not moult during culture, optical microscopy revealed a morphology typical of third-stage larvae. Finally, the genetic identity between the larval parasites collected from mullet Mugil curema and adult female parasites collected from the brown pelican suggests a life cycle of C. multipapillatum in which the mullet are involved as intermediate/paratenic hosts and the brown pelicans as final hosts in the geographical area of Bahía de La Paz.

A scanning electron microscopy study of early development in vitro of Contracaecum multipapillatum s.l. (Nematoda: Anisakidae) from a brown pelican (Pelecanus occidentalis) from the Gulf of California, Mexico.

Eggs obtained from the uteri of female nematodes, genetically identified as Contracaecum multipapillatum s.l., found in a brown pelican (Pelecanus occidentalis) from Bahía de La Paz, Gulf of California, Mexico, were used to study the early developmental stages of this anisakid by scanning electron microscopy (SEM). Egg dimensions were approximately 54 × 45 µm measured by SEM. Observation of the eggs revealed an outer surface of fibrous appearance. The newly hatched larvae were ensheathed and highly motile. Observation with SEM showed that the sheaths of the larvae were striated and revealed an excretory pore and a cleft near the anterior end of the sheath, presumably to facilitate the opening of the sheath for the emergence of the larva. The hatched larvae were placed in nutritive culture medium, where they grew within their sheath, some exsheathing completely 2 weeks later. The surface patterns of the sheath and the cuticle of the exsheathed larvae were clearly different. Although they did not moult during culture, SEM revealed a morphology typical of third-stage larvae of Contracaecum from fish, as previously observed by optical microscopy. Thus, we suggest that newly hatched larvae from eggs of C. multipapillatum are third larval stage but with sheath of the second larval stage, as occuring in other anisakids.