Lateralized aggression, a population-level bias toward one side during agonistic encounters, is well documented in vertebrates, but its direction varies: tetrapods show a left-side bias, while some teleost fish show the reverse. Whether this pattern extends to invertebrates with fundamentally different neural architecture remains largely untested. Using citizen-science video of 30 wild male-male contests across three cuttlefish species (Sepia officinalis, Acanthosepion pharaonis, Ascarosepion latimanus), we investigated whether cuttlefish show a population-level side bias during contests. Cuttlefish engaged opponents preferentially using their left side, matching the tetrapod direction despite sharing the ecological conditions more directly with fish. Laterality did not predict contest outcome, and the rarer (right-biased) phenotype showed no frequency-dependent advantage. This contrasts findings in the giant Australian cuttlefish (Sepia apama), where minority lateral phenotypes win disproportionately in large, high-density breeding aggregations. This discrepancy may reflect the smaller, more dispersed breeding groups typical of the species studied here, though low statistical power leaves this explanation speculative. We suggest the results are consistent with lateralized threat processing being a general, structure-independent principle rather than one tied to vertebrate brain architecture.
Freshwater prey rely on chemosensory information, such as predator dietary cues, to accurately assess local predation risk. Climate change is increasing the frequency of multiple environmental stressors that can disrupt how prey detect and respond to such cues, yet few studies have examined how stressors affecting different sensory modalities interact to shape antipredator behaviour. Here, we tested how paired stressors alter prey responses to predator dietary cues. Trinidadian guppies were exposed to two stressor combinations (warming + acidification and warming + turbidity) and received either predator dietary cues from Jack Dempsey cichlids or a water control. We then assessed shoaling index and area use as indicators of antipredator behaviour. Overall, increasing stressor intensity reduced antipredator responses, regardless of the sensory modalities affected. Our study highlights the need to examine a broader range of chemical cues and to better understand how multiple stressors shape predator-prey interactions in freshwater ecosystems.
Consequent upon growing concerns about the use of synthetic hormones, including melatonin, to improve fisheries and aquaculture, this study evaluated the effects of melatonin on the oxidative stress biomarkers of juvenile African catfish. One hundred and thirty-five fish were randomly assigned to groups receiving 0, 10, and 30 mg/L of melatonin in a static renewal system for 14 days, followed by seven days of melatonin withdrawal. Standard bioassays were used to quantify changes in plasma antioxidant and liver oxidative stress enzymes. The results showed significant duration- and concentration-dependent increases in plasma alanine transaminase, aspartate transaminase, and alkaline phosphatase levels compared to control groups (p <= 0.05). Contrarily, there were significant duration- and concentration-dependent reductions in liver superoxide dismutase and catalase, along with significant increases in malondialdehyde and glutathione activities (p <= 0.05). Interestingly, many of these changes persisted after melatonin was removed. These suggested that exogenous melatonin profoundly affected oxidative stress enzymes in juvenile catfish.
At present, very little is known about inflammatory mechanisms in the crustacean intestine. It could be driven by some evolutionarily conserved molecules, such as endogenous gasotransmitters (viz. NO/iNOS and H2S/CBS) and signalling components (viz. NF-& kcy;B/p65, Nrf2 and p38MAPK). To detect their tissue distribution and cellular localization in midgut, the freshwater crayfish Procambarus clarkii was used as a model organism and immunohistochemical (IHC) staining was performed. Data were representative of three independent experiments, each with n = 5. Results indicated that (1) both NO and H2S were present in midgut tissue, and iNOS and CBS could be responsible for their generation; (2) NOS-like immunoreactivity occurred primarily in the nucleus of adluminal epithelium, but the positive signals of CBS were mainly present in the cytoplasm; (3) NF-& kcy;B/p65 and p38 MAPK were diffusely distributed in the surface epithelium and lamina propria while Nrf2 densely lied in the nucleus of adluminal epithelium; (4) the positive signals of p38MAPK were more widely distributed than its phosphorylated form (p-p38MAPK), and p-p38 immunoreactivity was only observed in the nucleus but not in the cytoplasm. The epithelial cells and the molecules they produce might play a crucial part in mucosal immunity in crayfish gut.
Serrivomerid eels (Anguilliformes, Serrivomeridae) are present in the mid-latitude mesopelagic zone worldwide along with other mid-water eels. Nemichthyidae eels reportedly used vertically oriented body positions in the Atlantic Ocean, and submersible observations of vertical eels at the West Mariana Ridge (WMR) and southwestern Indian Ocean were mistakenly suggested to be nemichthyid eels. New up-close WMR observations in this study (May 2017) and examination of previous videos indicate that these vertical eels are serrivomerid eels and not nemichthyids, which have been seen behaving differently in underwater vehicles near Japan and elsewhere. During the five dives of the Shinkai 6500 Submersible (19-24 May 2017) made in a narrow study area to search for spawning anguillid eels along the WMR, at least seven vertically oriented eels were observed during three of the daytime dives at 650-850 m depths. Video recordings were obtained of four eels at 705-850 m during two dives (5.2-6.0 degrees C, salinity 34.5), and one was observed up-close at 850 m, with still camera images taken. This enabled confirmation that they belonged to the family Serrivomeridae, and likely the genus Serrivomer. There were two eels observed in the head-down and five in a head-up orientation, and one had a swollen abdomen, possibly from prey ingestion or developed gonads. Mesopelagic fishes, a large octopod, crustaceans, and gelatinous zooplankton were also observed at these depths where only a small amount of light reaches, so the vertical body orientation posture may be related to prey detection. Trichurids and some other fishes also use vertical body orientations, but existing video observations of nemichthyids do not show them using this type of behavior. Previously reported Atlantic observations were likely serrivomerids that appeared very slender and longer in comparison to images of specimens due to the ends of serrivomerid jaws breaking off during net capture.
