FISHERY BULLETIN: VOL 79. NO 4 



Okada et al. (1969) removed the brain from 

 A . superciliosus and compared it with the brains of 

 a number of other sharks in an effort to discern 

 a common structural pattern which might be 

 related to ecology or predatory behavior. They 

 concluded that brain morphology correlates with 

 ecology and behavior rather than with taxonomic 

 similarity since distantly related shark species 

 sharing similar behavior and habitat shared in 

 the development of a number of homologous brain 

 structures. According to Okada et al. the optic 

 tectum of A. superciliosus is well developed com- 

 pared with that of the common thresher and mako, 

 Isurus. Perhaps most noteworthy was the size of 

 the cerebellum, which was even larger than 

 the telencephalon. The reverse is usually found 

 (Figure 17). The brain of a 3 m A. superciliosus 

 weighed approximately 30 g, some one-third 

 heavier than that of a 3.6 m A. vulpinus. The 

 heavier brain of A. superciliosus reflects the 

 prominence of the optic lobes. Speculations as to 

 the significance of these structures would be 

 premature because of the paucity of physiological 

 data on shark brains. 



Two further studies have used the bigeye 

 thresher as a laboratory subject. Bundschuh and 

 Ballester (1971) tested the serum of 10 shark 

 species including the bigeye thresher for anti- 

 bodies against human saliva, erythrocytes, 

 and serum. Natural antibodies against human 

 proteins were reported, although the significance 

 of these antibodies was unclear. Finally, Gabeva 

 and Kovaleva (1976) described morphological 

 changes associated with spermatogenesis m the 



CER 



:^^SII3 



Figure 17. — Lateral views of the brains of Alopias super- 

 ciliosus (upper) and Carcharhinus sp. (lower) after Okada et al. 

 ( 1969). Brains have been sketched with telencephalon iTEL) the 

 same size. Note that the optic tectum lOPT) and cerebellum 

 (CER) are relatively much larger in the bigeye thresher. 



636 



bigeye thresher, and the role of the follicular 

 epithelium of the testes in the process. 



The dearth of experimental studies on 

 the bigeye thresher points to the difficulty of 

 obtaining fresh material for detailed analysis. 

 Because of this and because the bigeye thresher 

 has never been kept in captivity, it does 

 not ordinarily make a suitable subject for experi- 

 mental or detailed study. 



PARASITOLOGY 



The known parasite fauna of the bigeye 

 thresher has been given in five papers: three on 

 gut cestodes and two on external copepods. Dailey 

 (1969) erected the order Litobothridea to include 

 some unusual tapeworms he found in massive 

 infections of the spiral valve of two bigeye 

 threshers collected in southern California. Two 

 worms, Litobothrium alopias and L. coniformis, 

 were described as new species. Kurochkin and 

 Slankis (1973) further described L. daileyi and 

 Renyxa amplifica from the spiral valve of bigeye 

 threshers also from the Pacific Ocean. Thus, it 

 would appear that this group of cestodes has 

 evolved along with the Alopiidae and may 

 be restricted to that family Finally, Heinz and 

 Dailey (1974) reported two cestodes from the 

 stomach of the bigeye thresher: Sphyriocephalus 

 viridis and S . pelorosoma, the latter a new species. 



The only other parasites reported from the 

 bigeye thresher were two new species of copepods: 

 Pagina tunica and Banaka alopiae. Pagina tuni- 

 cata was removed from the body surface while 

 B. alopiae was taken from the gills (Cressey 1964, 

 1966). Cressey collected the type-specimen of 

 B. alopiae from bigeye threshers captured 

 off Madagascar and South America at stations 

 separated by almost 20,000 km. Because of this 

 great distance Cressey speculated that B. alopiae 

 has a specific affinity for the bigeye thresher. 



These few species probably do not represent 

 a complete catalogue of parasites infecting 

 the bigeye thresher, but rather are noteworthy 

 examples. If the bigeye thresher is similar to other 

 shark species, it harbors a diverse assemblage of 

 macroparasites including cestodes, nematodes, 

 leeches, copepods, and amphipods. 



COMMERCIAL IMPORTANCE 



Commercial exploitation of threshers, espe- 

 cially the bigeye thresher, follows two fishery 



