Possible involvement of phosphatidylcholine in school recognition in the catfish, Plotosus lineatus

No evidence for individual recognition in threespine or ninespine sticklebacks (Gasterosteus aculeatus or Pungitius pungitius)

Recognition plays an important role in the formation and organization of animal groups. Many animals are capable of class-level recognition, discriminating, for example, on the basis of species, kinship or familiarity. Individual recognition requires that animals recognize distinct cues, and learn to associate these with the specific individual from which they are derived. In this study, we asked whether sticklebacks (Gasterosteus aculeatus and Pungitius pungitius) were capable of learning to recognize individual conspecifics. We have used these fish as model organisms for studying selective social learning, and demonstrating a capacity for individual recognition in these species would provide an exciting opportunity for studying how biases for copying specific individuals shape the dynamics of information transmission. To test for individual recognition, we trained subjects to associate green illumination with the provision of a food reward close to one of two conspecifics, and, for comparison, one of two physical landmarks. Both species were capable of recognizing the rewarded landmark, but neither showed a preference for associating with the rewarded conspecific. Our study provides no evidence for individual recognition in either species. We speculate that the fission-fusion structure of their social groups may not favour a capacity for individual recognition.

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.

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.

Familiarity affects social network structure and discovery of prey patch locations in foraging stickleback shoals

Numerous factors affect the fine-scale social structure of animal groups, but it is unclear how important such factors are in determining how individuals encounter resources. Familiarity affects shoal choice and structure in many social fishes. Here, we show that familiarity between shoal members of sticklebacks (Gasterosteus aculeatus) affects both fine-scale social organization and the discovery of resources. Social network analysis revealed that sticklebacks remained closer to familiar than to unfamiliar individuals within the same shoal. Network-based diffusion analysis revealed that there was a strong untransmitted social effect on patch discovery, with individuals tending to discover a task sooner if a familiar individual from their group had previously done so than if an unfamiliar fish had done so. However, in contrast to the effect of familiarity, the frequency with which individuals had previously associated with one another had no effect upon the likelihood of prey patch discovery. This may have been due to the influence of fish on one another's movements; the effect of familiarity on discovery of an empty ‘control’ patch was as strong as for discovery of an actual prey patch. Our results demonstrate that factors affecting fine-scale social interactions can also influence how individuals encounter and exploit resources.

Phosphatidylcholine profile-mediated group recognition in catfish

Animal groups are integrated by emission of discrete signals from members, so-called social signals, which have evolved for each species. Among communication signals, chemical signals play an important role for recognition of group membership. The catfish Plotosus lineatus forms a dense school immediately after hatching, and school recognition is under the control of chemical signals emitted by the school members. The key substance(s) governing this recognition are deduced to be a mixture of phosphatidylcholines (PC). To substantiate this hypothesis that a mixture of PC molecular species functions as recognition of school-specific odor, we examined the ability of P. lineatus to discriminate between familiar and unfamiliar PCs. P. lineatus responded only to PCs from a familiar school, and not to those from unfamiliar schools. PC molecular species were then analyzed by quantitative high performance liquid chromatography, which resulted in not only a complex mixture of PC molecular species, but also school-specific PC profiles. Furthermore, multivariate analysis of the quantified PC peaks revealed the presence of various PC profiles. Finally, we showed that the modification of PC profiles disrupts the recognition of school odor in P. lineatus. Therefore, we conclude that the recognition of school odor in P. lineatus is governed by school-specific PC profiles.

Social recognition in wild fish populations

The ability of animals to gather information about their social and physical environment is essential for their ecological function. Odour cues are an important component of this information gathering across taxa. Recent laboratory studies have revealed the importance of flexible chemical cues in facilitating social recognition of fishes. These cues are known to be mediated by recent habitat experience and fishes are attracted to individuals that smell like themselves. However, to be relevant to wild populations, where animals may move and forage freely, these cues would have to be temporally flexible and allow spatial resolution. Here, we present data from a study of social recognition in wild populations of three-spined sticklebacks (Gasterosteus aculeatus). Focal fish preferentially associated with conspecifics from the same habitat as themselves. These preferences were changed and updated following translocation of the focal fish to a different site. Further investigation revealed that association preferences changed after 3 h of exposure to different habitat cues. In addition to temporal flexibility, the cues also allowed a high degree of spatial resolution: fish taken from sites 200 m apart produced cues that were sufficiently different to enable the focal fish to discriminate and associate with fish captured near their own home site. The adaptive benefits of this social recognition mechanism remain unclear, though they may allow fish to orient within their social environment and gain current local information.