Multiple reproduction forms in the polyps of the cannonball jellyfish Stomolophus sp. 2: Probable life-cycle reversal.

The jellyfish genera Stomolophus spp. is one of the most abundant in the Pacific Ocean, yet it has not been thoroughly studied. Until recently, research has been developed and directed to its knowledge because of the economic interest in its exploitation. The genus Stomolophus in the Pacific Ocean is composed of five species (S. agaricus, S. chunii, S. collaris, S. fritillaria, and S. meleagris), and Stomolophus sp. 2 has been recently reported in the central part of the Gulf of California. Therefore, this study aimed to describe in vivo the different developmental stages of Stomolophus sp. 2 life cycle. As a result, multiple polyp reproduction forms were described, such as polyp-stolon formation, polydisc strobilation with more than 20 ephyrae formed by each strobila, and polyp formation directly from juvenile ephyra. In the degenerating phase, the polyps turned into cysts induced by stress conditions, such as changes in temperature, oxygen, and food availability. The life cycle of Stomolophus sp. 2 can be distinguished from that of S. meleagris by showing various asexual reproduction mechanisms and polydisc-like strobilation. The formation of polyps directly from the ectoderm of degenerating juvenile medusae suggests the possibility of a reversion cycle. Because of the different life cycles between S. meleagris and S. sp. 2, in addition to their morphological and genetic differences, this study proposes that Stomolophus sp. 2 should be considered a new species and suggests the name Stomolophus yaquilli, in reference to the indigenous community that lives in the species distribution area.

The white spot syndrome virus hijacks the expression of the Penaeus vannamei Toll signaling pathway to evade host immunity and facilitate its replication.

The white spot syndrome virus (WSSV), the most lethal pathogen of shrimp, is a dsDNA virus with approximately a 300,000 base pairs and contains approximately 180-500 predicted open reading frames (ORFs), of which only 6% show homology to any known protein from other viruses or organisms. Although most of its ORFs encode enzymes for nucleotide metabolism, DNA replication, and protein modification, the WSSV uses some of its encoded proteins successfully to take control of the metabolism of the host and avoid immune responses. The contribution of the shrimp innate immune response to prevent viral invasions is recognized but yet not fully understood. Thus, the role of several components of Toll pathway of the shrimp Penaeus vannamei against WSSV has been previously described, and the consequential effects occurring through the cascade remain unknown. In the current study the effects of WSSV over various components of the shrimp Toll pathway were studied. The gene expression of Spätzle, Toll, Tube, Cactus and Dorsal was altered after 6-12 h post inoculation. The expression of LvToll3, LvCactus, LvDorsal, decreased ~4.4-, ~3.7- and ~7.3-fold at 48, 24 and 48 hpi, respectively. Furthermore, a remarkable reduction (~18-fold) in the expression of the gene encoding LvCactus in WSSV infected specimens was observed at 6 hpi. This may be a sophisticated strategy exploited by WSSV to evade the Toll-mediated immune action, and to promote its replication, thereby contributing to viral fitness.

Association of the whale shark Rhincodon typus with the cannonball jellyfish Stomolophus meleagris.

This study describes the first record of the whale shark Rhincodon typus association with the cannonball jellyfish Stomolophus meleagris in the Gulf of California, Mexico. Whale sharks were observed swimming and feeding among swarms of jellyfish, suggesting competition and predatory behaviour given the overlap in food preferences between both species. This finding is relevant because of the species-wide distribution and the importance of these interactions, which should be considered in conservation strategies of R. typus and management of cannonball jellyfish fisheries.

Production response and digestive enzymatic activity of the Pacific white shrimp Litopenaeus vannamei (Boone, 1931) intensively pregrown in microbial heterotrophic and autotrophic-based systems.

Shrimp postlarvae were reared into different microcosm systems without water exchange; a traditional system based on simple fertilization to improve microalgae concentration (control), an autotrophic system (AS) based on the promotion of biofloc and biofilm by the addition of fertilizer and artificial substrates and a heterotrophic system (HS) based on the promotion of heterotrophic bacteria by the addition of nitrogenous and carbonaceous sources and artificial substrates. Better growth performance and survival were registered in shrimp from the AS and HS compared to the control. Feed conversion ratios were below 0.7 for all treatments, but AS and HS were significantly lower than the control. Regarding digestive performance, no significant differences were observed for trypsin, amylase and lipase activities among AS and control shrimp; however, shrimp from HS showed a higher trypsin and amylase activities, suggesting a higher digestive activity caused by the presence of microbial bioflocs. The presence of biofilm and bioflocs composed by either autotrophic or heterotrophic organisms in combination with formulated feed improved the growth performance and survival of shrimp. Apparently, such combination fits the nutritional requirements of shrimp.