Measurements were made on the intact retinae dissected from freshly caught deep-sea fish. The unbleached retinae of such fish are not rose-pink like the retinae of most coastal fish or purple like the retinae of most freshwater fish, but are golden in colour.The golden colours are of photosensitive pigments which give retinal absorption curves similar in shape to frog's rhodopsin, but with maxima of absorption displaced on the average about 15 mμ. towards the blue end of the spectrum. The names ‘chrysopsins’ or visual golds are suggested for this group of pigments.The density of such photosensitive pigments is often very high. Retinal density changes on bleaching of more than 1.0 has been found for several deepsea fish. These probably correspond to absolute retinal densities of pigment of about 1.3, i.e. the absorption of 95% of blue-green light striking the retina.The conger and silver freshwater eels have retinae containing similar golden-coloured pigments. These eels begin their lives in the deep ocean and return there when mature to spawn.The significance of this type of photosensitive pigment in the vision of deep-sea fish is discussed, and an estimate is made of the depths at which deepsea fish will see daylight.

Abstract:Temperate wetlands are generally net retainers of sulphate (SO 4 2 ). However, recent research indicates that some wetlands may export SO 4 2 during drought conditions. In temperate wetlands, the susceptibility to drought will depend on wetland-stream and groundwater-surface water interactions. Here we present results of summer SO 4 2 dynamics in a confined and unconfined stream within a temperate swamp.At the confined transect, the water table levels dropped greatly ( 55 cm) and groundwater flow patterns reversed in response to summer drought. Although high porewater SO 4 2 concentrations (36Ð4 mg l 1 ) were measured, no downstream export of SO 4 2 was observed. A SO 4 2 mass balance analysis on this stream reach indicated near zero retention. At the unconfined transect, water flowed from the stream to the wetland throughout most of the summer, maintaining relatively high water table levels ( 25 cm). Sulphate porewater concentrations were significantly lower (9Ð2 mg l 1 ) than in the confined transect. Downstream discharge decreased to zero within this reach during extreme drought conditions, resulting in 100% SO 4 2 retention for a three-week period. Upon rewetting stream SO 4 2 levels increased to 161Ð7 mg l 1 resulting in a large net export of SO 4 2 . This study demonstrates that while water table position was an important control on SO 4 2 dynamics within the wetland, the degree of hydrologic connectivity between the wetland and the stream was the main control on episodic SO 4 2 release following summer drought.

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