THE FAILURE OF HYPOPHYSECTOMIZED FUNDULUS HETEROCLITUS TO SURVIVE IN FRESH WATER

¹ The Bingham Oceanographic Laboratory, Yale University, New Haven, Connecticut

1. Hypophysectomy results in a loss of ability to survive in fresh water by the euryhaline cyprinodont, Fundulus heteroclitus. The average survival time is 6-7 days for salt water-adapted fish. Preadaptation in fresh water before operation may prolong survival but does not prevent ultimate death.

2. Hypophysectomized fish are unable to survive in salinities up to 13 %o.

3. Symptoms of death are those of asthenia accompanied by a slight weight increase, averaging 4.3% in fish not being handled daily.

4. Serum chloride determinations showed that normal fish in either fresh or salt water maintain a uniform level of ca. 0.886 gm.% NaCl. Serum of hypophysectomized fish in salt water is not significantly lower (ca. 0.817 gm.%). Hypophysectomized fish dying in fresh water have only ca. 0.383 gm.%.

5. Replacement therapy with Fundulus pituitary brei enabled hypophysectomized fish to survive in fresh water. Pituitary extract from Perca flavescens, a strictly fresh water species, was partially effective, whereas extracts from glands of Pollachius virens/, a marine species, had no beneficial influence.

6. Injections of ACTH, GH, TSH, thyroxin, DOCA, posterior lobe extract, and an ACTH-GH-TSH combination failed to enable the fish to survive in fresh water.

7. The data presented above appear to indicate that the pituitary of F. heteroclitus secretes an unknown factor(s) which regulates salt balance in that fish in fresh water. This factor is apparently lacking in the stenohaline marine species, P. virens, but may be present in the fresh water species, P. flavescens.

8. Hypophysectomy has no effect on the cytology of the chloride cells either in the active (sea water) or regressed (fresh water) condition.

9. Mucous cells were more abundant in the gills of normal fish when adapted to fresh water than when adapted to salt water. Hypophysectomy resulted in atrophy of the mucous cells in either medium and a decreased abundance in fish dying in fresh water. The abundance and condition of the mucous cells was restored to normal in hypophysectomized fish which were induced to survive in fresh water by injections of Fundulus pituitary brei.

10. The data suggest that the chloride cells are not concerned in the failure of hypophysectomized fish to survive in fresh water, but that atrophy of the mucous cells may be involved.

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