Huffmanela cf. Carcharhini (Nematoda: Trichosomoididae: Huffmanelinae) from Skin of a Sandbar Shark, Carcharhinus plumbeus, in the Pacific Ocean

Abstract

Eggs of Huffmanela cf. carcharhini from the skin of an aquarium-held, juvenile sandbar shark, Carcharhinus plumbeus , from the Pacific Ocean were studied using light and scanning electron microscopy. Grossly, eggs imparted a scribble-like skin marking approximately 130 × 60 mm on the right side of the shark's snout adjacent to its eye and nostril. Fresh (unfixed) eggs were elliptical, 75-95 µm long (x¯ = 85 µm, SD = ±4.5; n = 75), 48-63 µm wide (53 ± 3.4; 75), 8-10 µm in shell thickness (9 ± 1.3; 27), 45-68 µm in vitelline mass length (52 ± 6.9; 8); had a smooth shell surface and nonprotruding polar plugs 8-13 µm wide (10 ± 1.5; 73); lacked thin filaments, superficial envelope, and shell spines; sank in 35 ppt artificial seawater; and did not spontaneously hatch after 12 hr in 35 ppt artificial seawater. Formalin-fixed eggs measured 193 days postfixation were 75-95 µm long (84 ± 3.9; 150), 45-60 µm wide (50 ± 2.2; 150), 5-10 µm in shell thickness (8 ± 1.2; 87), 45-60 µm in vitelline mass length (51 ± 3.0; 92), and 30-40 µm in vitelline mass width (33 ± 2.0; 84), and had nonprotruding polar plugs that were 10-15 µm long (11 ± 1.4; 93) and 8-10 µm wide (9 ± 1.1; 108). Forcibly hatched first-stage larvae (unfixed) were filiform, 188-273 µm long (212 ± 25.5; 13), 8-13 µm wide (10 ± 1.2; 13), and had fine transverse striations. Eggs infected the epidermis only. Histology revealed intra-epithelial inflammation with eosinophilic granulocytes and hyperplasia, plus dermal lymphofollicular hyperplasia associated with the infection. The eggs of H. cf. carcharhini likely undergo considerable ex utero development before being sloughed (unhatched) from the host, along with epidermal cells.