SWIMBLADDER DEVELOPMENT AND FUNCTION IN THE HADDOCK, MELANOGRAMMUS AEGLEFINUS L

¹ Department of Zoology, University of California, Berkeley, California 94720

The swimbladder in the haddock appears on the 11th day of embryogenesis as a dorsal outgrowth of the gut just posterior to the liver diverticulum. In later stages its true position just anterior to the liver becomes visible.

Swimbladder inflation occurs very soon after yolk sac absorption. At this time the larvae measure 4-4.5 mm and have begun feeding.

Haddock larvae probably do not swallow air to fill their swimbladders. The initial gas volume may be derived from glycogenolysis, as glycogen is present in substantial amounts in uninflated swimbladder epithelium. Glycogen is absent from the paravascular portions of the epithelium in inflated swimbladders but is well-represented elsewhere in the cells.

It is proposed that the inflated swimbladder in larvae less than 8.0 mm serves to decrease their density and thereby carry them up towards the level of the forming thermocline. By the time the thermochine is well-established, the larvae are larger and of greater swimming ability, and with the aid of a functioning swim-bladder should be able to maintain themselves within it.