Phosphatidylcholine profile-mediated group recognition in catfish

Heat induces multiomic and phenotypic stress propagation in zebrafish embryos

Heat alters biology from molecular to ecological levels, but may also have unknown indirect effects. This includes the concept that animals exposed to abiotic stress can induce stress in naive receivers. Here, we provide a comprehensive picture of the molecular signatures of this process, by integrating multiomic and phenotypic data. In individual zebrafish embryos, repeated heat peaks elicited both a molecular response and a burst of accelerated growth followed by a growth slowdown in concert with reduced responses to novel stimuli. Metabolomes of the media of heat treated vs. untreated embryos revealed candidate stress metabolites including sulfur-containing compounds and lipids. These stress metabolites elicited transcriptomic changes in naive receivers related to immune response, extracellular signaling, glycosaminoglycan/keratan sulfate, and lipid metabolism. Consequently, non-heat-exposed receivers (exposed to stress metabolites only) experienced accelerated catch-up growth in concert with reduced swimming performance. The combination of heat and stress metabolites accelerated development the most, mediated by apelin signaling. Our results prove the concept of indirect heat-induced stress propagation toward naive receivers, inducing phenotypes comparable with those resulting from direct heat exposure, but utilizing distinct molecular pathways. Group-exposing a nonlaboratory zebrafish line, we independently confirm that the glycosaminoglycan biosynthesis-related gene chs1 and the mucus glycoprotein gene prg4a, functionally connected to the candidate stress metabolite classes sugars and phosphocholine, are differentially expressed in receivers. This hints at the production of Schreckstoff-like cues in receivers, leading to further stress propagation within groups, which may have ecological and animal welfare implications for aquatic populations in a changing climate.

Swim with the tide: Tactics to maximize prey detection by a specialist predator, the greater sea snake (Hydrophis major)

The fitness of a predator depends upon its ability to locate and capture prey; and thus, increasing dietary specialization should favor the evolution of species-specific foraging tactics tuned to taxon-specific habitats and cues. Within marine environments, prey detectability (e.g., via visual or chemical cues) is affected by environmental conditions (e.g., water clarity and tidal flow), such that specialist predators would be expected to synchronize their foraging activity with cyclic variation in such conditions. In the present study, we combined behavioral-ecology experiments on captive sea snakes and their prey (catfish) with acoustic tracking of free-ranging sea snakes, to explore the use of waterborne chemical cues in this predator-prey interaction. In coral-reef ecosystems of New Caledonia, the greater sea snake (Hydrophis major) feeds only upon striped eel catfish (Plotosus lineatus). Captive snakes became more active after exposure to waterborne chemical cues from catfish, whereas catfish did not avoid chemical cues from snakes. Movement patterns of tracked snakes showed that individuals were most active on a rapidly falling tide, which is the time when chemical cues from hidden catfish are likely to be most readily available to a foraging predator. By synchronizing foraging effort with the tidal cycle, greater sea snakes may be able to exploit the availability of chemical cues during a rapidly falling tide to maximize efficiency in locating and capturing prey.

Biological and Ecological Roles of External Fish Mucus: A Review

Fish mucus layers are the main surface of exchange between fish and the environment, and they possess important biological and ecological functions. Fish mucus research is increasing rapidly, along with the development of high-throughput techniques, which allow the simultaneous study of numerous genes and molecules, enabling a deeper understanding of the fish mucus composition and its functions. Fish mucus plays a major role against fish infections, and research has mostly focused on the study of fish mucus bioactive molecules (e.g., antimicrobial peptides and immune-related molecules) and associated microbiota due to their potential in aquaculture and human medicine. However, external fish mucus surfaces also play important roles in social relationships between conspecifics (fish shoaling, spawning synchronisation, suitable habitat finding, or alarm signals) and in interspecific interactions such as prey-predator relationships, parasite–host interactions, and symbiosis. This article reviews the biological and ecological roles of external (gills and skin) fish mucus, discussing its importance in fish protection against pathogens and in intra and interspecific interactions. We also discuss the advances that “omics” sciences are bringing into the fish mucus research and their importance in studying the fish mucus composition and functions.

Chemicals released by male sea cucumber mediate aggregation and spawning behaviours

The importance of chemical communication in reproduction has been demonstrated in many marine broadcast spawners. However, little is known about the use of chemical communication by echinoderms, the nature of the compounds involved and their mechanism(s) of action. Here, the hypothesis that the sea cucumber Holothuria arguinensis uses chemical communication for aggregation and spawning was tested. Water conditioned by males, but not females, attracted both males and females; gonad homogenates and coelomic fluid had no effect on attraction. Male spawning water, but not female spawning water, stimulated males and females to release their gametes; the spermatozoa alone did not induce spawning. H. arguinensis male spawning water also induced spawning in the phylogenetically related H. mammata. This indicates that males release pheromones together with their gametes that induce spawning in conspecifics and possibly sympatric species. Finally, the male pheromone seems to be a mixture with at least one labile compound (biological activity is lost after four hours at ambient temperature) possibly including phosphatidylcholines. The identification of pheromones in sea cucumbers offers a new ecological perspective and may have practical applications for their aquaculture.

The clinical effects of the venomous Lessepsian migrant fish Plotosus lineatus (Thunberg, 1787) in the Southeastern Mediterranean Sea

CONTEXT

Plotosus lineatus is a venomous fish that has migrated from the Indo-Pacific region to the Mediterranean Sea (Lessepsian migrant). Its presence in the Mediterranean Sea was first recorded in 2002 and was observed in growing schools. Its spines contain toxins with lytic, hemolytic and edematous activities.

OBJECTIVE

To characterize the injuries caused by Plotosus lineatus in the Southeastern Mediterranean Sea.

METHODS

A prospective observational case series of consultations provided by a national Poison Center pertaining to Plotosus lineatus from 2007 to 2016. Demographic and clinical data and method of fish identification were retrieved from the medical toxicological records, and described.

RESULTS

Eighty four cases were included; the main findings are: median age 35 (range 3-80) years, 91.7% males, 51.2% fishermen, 78.6% palm injuries, 94% and 4.8% were mildly and moderately injured, respectively. Main local manifestations included pain, puncture wound, swelling, and erythema (90.5%, 70.2%, 33.3%, and 16.7%, respectively). Systemic signs were minor and infrequent (≤7.1%), including hypertension, tachycardia, vomiting, chills, and weakness. Management included wound disinfection, immersion in hot water, tetanus prophylaxis, and analgesics. No patient required hospital admission. The fish was identified mostly by the victim with the aid of the Poison Center (mainly by typical description, and a picture), and some by marine biologists.

CONCLUSIONS

Plotosus lineatus is a new fish in the Southeastern Mediterranean Sea. It affects fishermen handling fishing nets, and beach hikers stepping on or holding it. Injuries caused by its spines usually result in minor effects; pain may be intense. Treatment includes disinfection, analgesics, and antitetanus and antibiotics as needed. No lethal cases were recorded, unlike exposure of animals to the venom of the Indo-Pacific species; reason is unclear. Our series illustrates the consequences of manmade disruption of ecosystem resulting in invasion of toxic species to a new environment, affecting human health.