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 Text and photos copyright John P. Hoover

past fishes of the month


Canthigaster jactator


Magic Island, O`ahu. 30 ft.
Canthigaster jactator (Jenkins, 1901)
     Tobies, sometimes called "sharpnose pufferfish" are diminutive puffers with a somewhat elongated snout. They are generally less than 4 inches long and constitute a subfamily within the larger pufferfish family, Tetraodontidae. Out of five species of tobies in Hawai`i, this is by far the most common. It is brown with white spots. The eye is green and the body often displays a slight green fluorescence. Usually in pairs, these fish occur on hard substrate just about everywhere, both in areas of 100% coral cover and in dead silty places where little else seems to live. Some individuals have irregular black marks on the snout, body, and fins—perhaps a disease. Others are so distended with parasitic worms (nematodes) that they appear inflated. One study indicated that Hawaiian Whitespotted Tobies feed mostly on green and red algae; another showed sponges to be the main food, followed by algae and tunicates. Aquarists have observed these cute but mischievous puffers stealthily approaching other fishes and nipping their fins, leaving perfect semicircular "cookie-bites" along the edges. They also nip at the skin of resting sea turtles, especially those with tumorous growths, causing the turtles to flinch. The species name means "boaster," or "braggart," no doubt because of the fish’s ability to inflate. It attains about 3.5 inches and is endemic to the Hawaiian Islands. Two similar sister species exist, C. janthinoptera in the Indo-Pacific (excluding Hawai`i) and C. punctatissima in the Eastern Pacific, both with smaller white spots.

Black marks - Magic Island, O`ahu. 20 ft.

Distended by nematode worms - Marty's Reef, South Maui, 50 ft

     Although the Hawaiian species has not been studied in detail, the similar Eastern Pacific White-Spotted Toby, Canthigaster punctatissima, has been found to be sexually dimorphic (males larger than females) with both sexes defending territories against others of their own sex. Male territories include the smaller territories of one to four females. The male pairs with each of his females at different times and his females never pair with other males. If a male is removed, his territory is absorbed into that of a neighboring male, often overnight. The lifestyle of C. jactator is likely similar, as demonstrated by a very small study performed in 1985 by
high school students Kim Bruno and Marguerite Nogues.
     During 5 scuba dives, Bruno and Nogues observed that the little puffers spent most of their time in pairs (although not necessarily next to or very near each other) and swam in a distinct pattern which seemed to mark circular territories that varied in diameter from three to twenty feet. (The students marked the territory boundaries with nails and observed that the tobies were curious, often inspecting these shiny foreign objects.) On one occasion a toby entered another pair’s area and one of the resident tobies swam out, nipped its side, and chased it away, indicating defense of a territory. The tobies spent about 50 percent of the daytime time swimming around the territory, 40 percent hiding among the rocks, and about 10 percent feeding.
      What do they do at night? We don't know much, but Wiilliam J. Walsh, while studying fish sheltering behavior in Kona, noted that a Hawaiian Whitespotted Toby rested at night on one of his polypropylene transect lines spanning a vertical wall. Although the line was essentially the same thoughout its length, the toby rested each night within an inch of the same precise spot for a period of over two weeks.

     Diving at Mäkua, O`ahu, photographer David R. Schrichte watched a pair of Canthigaster jactator apparently spawning. The fish on the right (presumably the male) pursued the fish with the swollen belly on the left (presumably the female) into a hole (photo #1). The swollen fish positioned itself repeatedly in a particular spot and trembled as if it were laying eggs (photo #2). A photo of a totally different pair at Kahe Point, O`ahu, seems to show a male (right) fertilizing eggs just laid by a still swollen female (photo #3).

1 - About to spawn? Photo copyright David R. Schrichte

2 - Laying eggs? - Photo copyright David R. Schrichte

3 - Male (in back) fertilizing eggs?
     Observing a Whitespotted Toby under ultraviolet light, University of Hawai`i researcher Jill P. Zamzow discovered some subtle spots on the fish that were visible only when its mucus was wiped off. The mucus was apparently blocking the ultraviolet light from her lamp. In nature, she surmised, UV-absorbing compounds in the mucus probably protect the fish from the sun’s damaging radiation. The UV-blocking capability of Whitespotted Toby mucus turned out to be equal in strength to SPF 15 human sunscreen. Intrigued, Zamzow examined the mucus of 200 other Indo-Pacific reef fishes, finding sunscreen compounds in 84 percent of them. One, the Hawaiian Saddle Wrasse (Thalassoma duperrey), was even able to change the SPF factor of its mucus depending upon the depth at which it lived.

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  Text and photos copyright John P. Hoover