On the structure of the poison spines of the Aigo (TEUTHIS 

 (SYN. SIGANUS ) FUSCESCENS ) "" 



The aigo belongs to the family Teuthidae, which according to Boulenger 

 comprises only the one genus Teuthis in which thirty species are included. 

 They are all herbivorous fishes which occur in the Indian Ocean and the West- 

 ern Pacific. They are all warm water fish and are distributed from the tem- 

 perate zone to the tropics. The aigo of Japan is distributed from the Tokyo 

 area south. It is of course herbivorous and commonly feeds on brown algae. 

 It occurs in shallow places where algae grow well. These fish are often seen 

 feeding on algae in small groups of up to fourteen individuals. 



Fishermen are very well acquainted with the fact that these fish have 

 poisonous spines, and they never handle the fish with their bare hands be- 

 cause of their fear of the painful wounds caused by being stuck by them. 

 Bottard was the first to reveal to the scientific world the presence of poison 

 in this fish. He cited this fish along with a large number of other poisonous 

 species. In recent years the Russian, Pawlowsky, has studied the anatomy and 

 histology of many poisonous fishes, particularly of such Japanese members of 

 the family Scorpaenidae as the okoze and kasago , various specimens of which 

 were sent to him by Mr. Shlgeho Tanaka of the Science Department. These 

 studies have been published, but as he had no specimens of the aigo he did not 

 study it. In my study of the poison gland of the aigo I have found that its 

 construction closely resembles that shown by Pawlowsky for fishes of the family 

 Scorpaenidae. 



The poison of the aigo is in the stiff spines of the fins. The fin ray 

 formula of the aigo is DTlcii or Xiii - 10, A. VII - 9, P. 16, V. I - 3 - I. 

 This means that there are 12 or 13 spines in the dorsal fin, 7 in the anal, 

 none in the pectorals, and two in each of the ventrals. These stiff spines 

 are all equipped with poison glands. This being the case, because of the 

 lack of spines in the pectoral fins the fish has these protective mechanisms 

 only on the back and belly and is not equipped with any defenses toward attacks 

 from the sides. In outward appearance most of the spines show an extremely 

 sharp tip protruding from the fin membrane, but in some cases the first two 

 or three spines of the dorsal, the spines of the ventrals, and the first one 

 or two spines of the anal are occasionally completely hidden and covered with 

 skin to their tips. Although the tips of the spines are originally naturally 

 covered completely, for some reason, perhaps because the poison spines have 

 once been used or because of contact with some foreign object, the soft skin 

 has in some cases retreated, exposing the tips of the spines. Even when they 

 are completely covered by the skin the tips of the spines are very sharp so 

 that if they are touched they immediately come through the skin and pierce the 

 object which touches them. A cross-section of one of the spines is shown in 

 Figure 1. In the center there is the cross-section of the hard keratose spine 

 (sp) with grooves in its right and left sides. These grooves lie longitudinally 

 along both sides of the spine. These long concavities are occupied by the 

 poison glands (pg)« The poison glands are completely surrounded by connective 

 tissue with a dermal and an epidermal layer on the outside. Under the epi- 

 dermal layer are chroma tophores (pgm) and in the epidermis are large single 

 cells which are mucus glands (eg). The connective tissue and the dermal and 

 epidermal layers continue on to form the fin membrane (fin) and connect with 

 the next spine. There is no muscular tissue visible aroiuid the spines. 



With regard to the question of the length of the poison glands, in the 

 aigo, as described above, they lie along the sides of tlie spines, and on all 

 of them they disappear a short distance from the insertion of the spine. Con- 



seouently the length of the poison gland varies according to the length of the 

 spine, the gland covering a rather long area on the longer spines. At the base 



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