SUMMARYSeveral factors that influence the evolution of the unusual head morphology of hammerhead sharks (family Sphyrnidae) are proposed but few are empirically tested. In this study we tested the 'enhanced binocular field' hypothesis (that proposes enhanced frontal binocularity) by comparison of the visual fields of three hammerhead species: the bonnethead shark, Sphyrna tiburo, the scalloped hammerhead shark, Sphyrna lewini, and the winghead shark, Eusphyra blochii, with that of two carcharhinid species: the lemon shark, Negaprion brevirostris, and the blacknose shark, Carcharhinus acronotus. Additionally, eye rotation and head yaw were quantified to determine if species compensate for large blind areas anterior to the head. The winghead shark possessed the largest anterior binocular overlap (48deg.) and was nearly four times larger than that of the lemon (10deg.) and blacknose (11deg.) sharks. The binocular overlap in the scalloped hammerhead sharks (34deg.) was greater than the bonnethead sharks (13deg.) and carcharhinid species; however, the bonnethead shark did not differ from the carcharhinids. These results indicate that binocular overlap has increased with lateral head expansion in hammerhead sharks. The hammerhead species did not demonstrate greater eye rotation in the anterior or posterior direction. However, both the scalloped hammerhead and bonnethead sharks exhibited greater head yaw during swimming (16.9deg. and 15.6deg., respectively) than the lemon (15.1deg.) and blacknose (15.0deg.) sharks, indicating a behavioral compensation for the anterior blind area. This study illustrates the larger binocular overlap in hammerhead species relative to their carcharhinid sister taxa and is consistent with the 'enhanced binocular field' hypothesis. Supplementary material available online at

Incidental capture, or bycatch, of elasmobranchs (sharks, skates, and rays) threatens populations worldwide. In this review, elasmobranch sensory biology and ecology are explored to identify potential species- and fishery-specific bycatch reduction techniques for a variety of fishing gear types.

SUMMARYThe visual fields of elasmobranch fishes are not well characterized even though this is a fundamental element of the visual system. The batoid fishes (skates, rays) form a monophyletic clade within the subclass Elasmobranchii and exhibit a broad range of morphologies and corresponding ecologies. We hypothesized that their visual field characteristics would reflect their diverse morphology and ecology. This was tested by quantifying the monocular, binocular and cyclopean horizontal and vertical visual fields of four batoid species (Raja eglanteria, Urobatis jamaicensis, Dasyatis sabina and Rhinoptera bonasus) that encompassed a range from a basal skate to a more derived ray. The horizontal and vertical visual fields differed significantly among species; however, all species possessed horizontal anterior and dorsal binocular overlaps. Urobatis jamaicensis, a small reef-associated stingray, demonstrated a 360° panoramic visual field in the horizontal plane, and R. bonasus, a schooling benthopelagic ray, a 360° panoramic view in the vertical plane. Large anterior binocular overlaps were measured in D. sabina (72°) and R. bonasus (46°) but came at the expense of large posterior blind areas. The anterior binocular overlaps in R. eglanteria (28°) and U. jamaicensis (34°) were smaller but were coupled with large monocular fields that provided expansive peripheral views. The most phylogenetically basal species, the clearnose skate (Raja eglanteria), had the most reduced visual field in contrast to the more derived ray species. To our knowledge, this study represents the first comparative assessment of visual fields in basal vertebrates.

The objective of this experiment was to test the probiotic E¢nol s L during transportation of cardinal tetra, Paracheirodon axelrodi (Schultz). For the transportation, ¢sh were distributed in 18 plastic tanks, of which nine contained the E¢nol s L (10 mg L À 1 ; probiotic treatment) and the remaining had no probiotic (control treatment). Transport lasted 24 h and three di¡erent boxes of each treatment were sampled at 3, 12 and 24 h. Up to the 12-h sampling period, no sig-ni¢cant di¡erence in the survival was observed; on the other hand, survival was higher at the end of the transport (24 h) in the probiotic treatment. No significant di¡erence was found in dissolved oxygen and temperature between treatments. Conductivity, pH and alkalinity increased along the transport, but without a di¡erence between treatments. Ammonia increased in all treatments, although it was signi¢cantly lower in the probiotic group at 24 h. Cortisol levels were signi¢cantly higher in all transported ¢sh when compared with the basal values. At 24 h, cortisol levels in control ¢sh were signi¢cantly higher than those in the probiotic treatment.With the observed results, we are able to conclude that the probiotic E¢nol s L is e⁄cient during cardinal transport, lowering the mortality and helping maintain water quality possibly by lowering metabolic wastes.

Visual temporal resolution and scotopic spectral sensitivity of three coastal shark species (bonnethead Sphyrna tiburo, scalloped hammerhead Sphyrna lewini, and blacknose shark Carcharhinus acronotus) were investigated by electroretinogram. Temporal resolution was quantified under photopic and scotopic conditions using response waveform dynamics and maximum critical flicker-fusion frequency (CFF). Photopic CFF max was significantly higher than scotopic CFF max in all species. The bonnethead had the shortest photoreceptor response latency time (23.5 ms) and the highest CFF max (31 Hz), suggesting that its eyes are adapted for a bright photic environment. In contrast, the blacknose had the longest response latency time (34.8 ms) and lowest CFF max (16 Hz), indicating its eyes are adapted for a dimmer environment or nocturnal lifestyle. Scotopic spectral sensitivity revealed maximum peaks (480 nm) in the bonnethead and blacknose sharks that correlated with environmental spectra measured during twilight, which is a biologically relevant period of heightened predation.

No abstract

The objective of this experiment was to test the efficacy of a probiotic (Efinol®L) during transportation of marbled hatchetfish, Carnegiella strigata. Wild specimens were captured from a small stream and transported for 24 h in plastic fish boxes with a probiotic (10 mg L−1) and probiotic‐free water. The boxes were sampled at 3, 12 and 24 h of transport. At the end of the experiment, the survival rate was close to 100% in both treatments. Dissolved oxygen diminished with time in both treatments, but the probiotic group had significantly higher levels. Conductivity, pH and ammonia increased significantly during the transport, demonstrating higher levels in the probiotic‐free group. Fish from both treatments presented very high net Na+ and K+ effluxes after 3 h of transport. At 24 h, net K+ effluxes in fish of the probiotic treatment reached values close to zero and a significantly lower Na+ efflux was observed. Cortisol levels in both treatments at 3 and 12 h were significantly higher than that in control samples. Higher body cortisol levels were observed in the probiotic‐free group than that in the probiotic group at 3 and 12 h. The results demonstrate that addition of a probiotic during fish transport improves water quality and leads to fish presenting a lower stress response intensity.

No abstract