LENGTH-WEIGHT RELATIONSHIP, FOOD HABITS, PARASITES, 



AND SEX AND AGE DETERMINATION OF THE RATFISH, 



HYDROLAGUS COLLIEI (LAY AND BENNETT)' 



Allyn G. Johnson^ and Howard F. Horton^ 



ABSTRACT 



In the fall and winter of 1965-1967, 292 ratfish (Hydrolagus colliei) were collected from 

 four locations off the Pacific coast of Oregon. Specimens were examined for length-weight 

 relationships, food habits, parasites, and a method of sex and age determination. Equa- 

 tions describing the body weight-body length (snout to vent) relationships were log weight 

 = log —4.3217 -f 3.0546 log length for males, and log weight = log —4.1692 + 2.9720 

 log length for females. The food organisms most important to ratfish were shrimp 

 (Pandalus and Crago), mollusks (Musculus and Amphissa) , and echinoderms (Bri- 

 saster). Two occurrences of cannibalism were found in ratfish collected off Cape Arago, 

 Oreg. Infestations by Gyrocotyle ranged from 29 to 66% among samples from the four 

 locations. The copepod, Acanthochondria sp., was attached to the claspers of seven 

 males from Cape Arago. Eye-lens weights (wet and dry), vertebral radii, basal sections 

 of the dorsal spine and left pectoral fin, and body-length frequencies were studied, but 

 no accurate method of age determination was found. Tritors on the posterior side of 

 the vomerine dental plate may be indicative of age, but the precise relationship was not 

 determined. 



The ratfish, Hydrolagus colliei (Lay and Ben- 

 nett) , is a member of the class Chondrichthyes, 

 order Chamaeriformes, and family Chimaeridae 

 (Bailey, 1970) . Distributed from western Alas- 

 ka to northern Baja California (Koratha, 1960) , 

 this cartilaginous fish is the only chimaeroid 

 found on the Pacific coast of Canada and the 

 United States, Ratfish are of little economic 

 value, but their liver oil is an excellent lubricant 

 and could be used commercially (Clemens and 

 Wilby, 1961), Ratfish are an important source 

 of food for such commercial fishes as soupfin 

 sharks, Galeorhinus zyopterus (Nakatsu, 1957), 

 spiny dogfish, Squalus acanthias (Alverson and 

 Stansby, 1963), and Pacific halibut, Hippoglos- 



^ Technical Paper No. 3144, Oregon Agricultural Ex- 

 periment Station, Corvallis, Oreg. 



^ Department of Fisheries and Wildlife, Oregon State 

 University, Corvallis, OR 97331; present address: Na- 

 tional Marine Fisheries Service, Northwest Fisheries 

 Center, 2725 Montlake Boulevard East, Seattle, WA 

 98102. 



' Department of Fisheries and Wildlife, Oregon State 

 University, Corvallis, OR 97331. 



sus stenolepis (Thompson, 1915). Conversely, 

 ratfish are commonly caught in the trawls of 

 commercial fishermen who consider them a nui- 

 sance. Our study was conducted to help fill the 

 need for more information on the general biology 

 of this primitive fish (Bigelow and Schroeder, 

 1953; Crescitelli, 1969). 



Little information has been published on the 

 food habits of H. colliei. Dean (1906) reported 

 that Chimaera (Hydrolagus) colliei fed on small 

 isospondylous fishes, opisthobranchs, annelids, 

 crustaceans, mollusks, squids, and nudibranchs. 

 Olsson (1896) and Legendre (1944) reported 

 that Chimaera monstrosa fed on mollusks, dec- 

 opods, annelids, amphipods, echinoderms, and 

 coelenterates. 



Several studies have been conducted on the 

 p&rasites of H. colliei. Wardle (1932) reported 

 that most ratfish contained a pair of Gyrocotyle 

 urna in the anterior region (spiral valve) of the 

 intestine. Lynch (1945) concluded that G. wma 

 should be divided into G. urna and G. fimbriata. 

 Koratha (1960) examined two H. colliei from 



Manuscript accepted January 1972. 



FISHERY BULLETIN: VOL. 70, NO. 2, 1972. 



421 



