The shovelnose guitarfish (Pseudobatos productus) is the most abundant and economically important batoid in Gulf of California fisheries. Despite the importance of the guitarfish in the demersal ecosystem, its trophic relationships are poorly understood. Results from stomach content and stable isotope analysis indicate P. productus is a specialist predator that feeds on coastal benthic organisms, mainly crustaceans, followed by fishes and cephalopods in the Upper Gulf of California. Males and females did not differ in dietary composition and isotopic values. Pseudobatos productus displayed ontogenetic changes in the diet, with smaller, immature individuals having a more specialized diet and mature individuals becoming generalist predators. Size classes I (<570 mm) and II (>570 mm) fed almost exclusively on crustaceans (99.78% and 82.37 %IRI, respectively). Size class III (>832 mm) increased consumption of fishes (22.11 %IRI) and squid (6.54 %IRI). Ontogenetic diet shifts were strongly supported by the SIAR mixing model. Stomach content and stable isotope analyses classify P. productus as a second-order predator.

Food partitioning between species is a common strategy for avoiding resource competition which allows the coexistence of two or more species in the same place. In order to evaluate the feeding of four species of batoids regularly caught by artisanal fisheries in southern Brazil, the present study aimed to analyse and compare the diet of the four batoid species. The Chola guitarfish, Rhinobatos percellens, had a specialized diet, consisting predominantly of blue crabs Callinectes sp., followed by teleost fish. The Lesser guitarfish Zapteryx brevirostris also had a very specialized diet, consuming mainly on Polychaeta, followed by Caridea shrimp. The Cownose ray, Rhinoptera bonasus, fed mainly on Ophiuroidea, followed by Gastropoda and Bivalvia. Finally, the Rio skate Rioraja agassizi, fed on teleost fish, Gammaridae, Caridea shrimp and Dendrobranchiata shrimp. An analysis of similarity showed significant differences among species in their diet. The trophic levels of the batoids in this study are <4.0, placing them in intermediate trophic levels. The analysis of the diets indicates that feeding differs substantially among the four species, suggesting a partitioning of food resources available in the environment.

Twelve parasitic copepod species representing two families were opportunistically recorded from the skin of 13 elasmobranch species captured in the coastal waters of Oman. New host records include Alebion carchariae, Pandarus smithii and Pandarus cranchii on Carcharhinus amboinensis; Echthrogaleus denticulatus on Alopias superciliosus and Sphyrna lewini; Pandarus carcharhini on Carcharhinus altimus; Pseudopandarus longus on Carcharhinus sorrah; Caligus dasyaticus on Glaucostegas halavi. Previous records of Pseudopandarus australis are limited to the Pacific Ocean, and its occurrence in the northern Indian Ocean represents a large range extension.

The capture of two Gorgona guitarfish, Rhinobatos prahli, in the Gulf of Tehuantepec represents the first record for the species in Mexican waters and its northernmost range extension in the eastern Pacific.

An adult female of the guitarfish Rhinobatos percellens with a total length of 550 mm was captured with a bottom trawl net on the southern coast of Brazil. This female bore five developing embryos, one of which had two heads and pectoral fins separated from the heads. This malformation is described here as the first instance for R. percellens.