Takuzo Abe

Histological structure of the male reproductive organs and spermatogenesis in a copulating sculpin, Radulinopsis taranetzi (Scorpaeniformes: Cottidae)

Characteristics of the structure and function of male reproductive organs in the copulating sculpin Radulinopsis taranetzi were investigated based on histological observations. The male reproductive organs comprised three parts: a pair of testes, a seminal vesicle, and a penis. Germinal cells matured in cysts located in the small seminal lobules. Asynchronous spermatogenesis advanced rapidly from the posterior to the anterior region of the testes. After sperm matured in the posterior part of the testes, the seminiferous epithelium of the seminal lobules synthesized and secreted eosinophilic fluid that showed a positive periodic acid–Schiff (PAS) reaction into the seminal lobules. Spermatozoa excreted from the posterior part of the testes were stored together with the secretion in the seminal vesicle and showed no activity in the seminal fluid. Histological observations throughout the year suggest that the fluid is secreted and spermatozoa are stored in the seminal vesicles during February to July, which is presumably when mating occurs. The importance of testicular maturation and the secretion of eosinophilic fluid during this long reproductive period is also discussed.

Why does the ocean sunfish bask

Basking at the sea surface is a well known, but peculiar behavior of ocean sunfish (Mola mola). One of hypotheses for this behavior is parasite elimination. However, in oceanic regions, very little direct evidence exists for this form of interspecific communication. In pelagic waters of the North Pacific Ocean, we observed a school of 57 ocean sunfish, that were heavily infested around the base of their dorsal fins with the ecto-parasite Pennella sp. We photographed a Laysan albatross (Phoebastria immutabilis) nearby that picked a Pennella sp. from one of ocean sunfish and ate it. We hypothesize that ocean sunfish did “bask” to look for skin cleaning and that this symbiotic cleaning behavior by the albatrosses may be a common feature of the biology of the ocean sunfish. Here we provide more photographs to show heavy parasite infections and scars after parasite removal by “cleaners,” and discuss how important a symbiotic cleaning relationship could be in the open ocean ecosystem.

Ontogenetic metamorphosis and extreme sexual dimorphism in lumpsuckers: Eumicrotremus asperrimus, Cyclopteropsis bergi and Cyclopteropsis lindbergi, may be synonymous

Cyclopterids were hatched from egg batches that were laid in two empty buccinid snail shells collected from a depth of 340 m in the Sea of Japan. Larvae were reared to identify species and to describe the morphological changes associated with metamorphosis. The fin rays of all fins were mostly complete and the pelvic fins were modified to form suckers, or adhesive discs, at the time of hatching. Juveniles immediately attached themselves to the bottom and there was no planktonic stage. The body surface was smooth with no spines or bony tubercles. At 4 months after hatching, the fine spines present on the head and trunk of juveniles transformed into bony tubercles. At 7 months after hatching, fishes became sexually dimorphic including the position and development patterns of bony tubercles. Importantly, these sexually dimorphic changes in morphology corresponded closely with descriptions of different species. Specifically, females could be classified as Eumicrotremus asperrimus, and young and fully developed males as Cyclopteropsis bergi and Cyclopteropsis lindbergi, respectively. These observations resolved a previously ambiguous hypothesis regarding the taxonomy of these cyclopterid taxa. Cyclopteropsis bergi and C. lindbergi may be synonyms of E. asperrimus.