Marine fish larvae typically are visual feeders and require a minimal light 

 intensity above 10-10 lux to feed optimally (14, 16). Light levels reported 

 by aquaculturists for successful culture of marine fish larvae have ranged from 

 250-10,000 lux (9, 42). A 500-3000 lux range has been used most often. A 

 minimum light intensity is necessary for initial detection of prey, visual 

 recognition and prey selection. At hght intensities close to the threshold level 

 there is a gradual reduction in larval activity and in feeding performance (16). 

 Blaxter (19) recently has summarized information on the anatomy of eyes in 

 fish larvae and also has discussed the development of vision. A pure cone 

 retina, which requires relatively high light intensities to be effective, appears to 

 be typical of larval stages of fish and such retinas have been identified in the 

 Atlantic herring (22), the plaice (12) and other species (19, 23). In general, for 

 the few species of larvae that liave been studied, the light intensity range in 

 which feeding activity decreases is approximately 10-10 lux (11, 12, 13). 

 This is near the dusk-dawn Hght intensity range of 10-10 lux (16). 



Laurence (60) estimated the number of hours required daily by winter 

 flounder larvae at 8°C to consume a ration that exceeds the maintenance 

 ration. For a prey concentration of 3.4 cal/1 (= 500 cope pod naupHi/1), the 

 minimum suitable for survival and growth, first feeding winter flounder larvae 

 would require about 20 hours per day to consume the maintenance ration. The 

 diurnal light period, when Ught intensities are above 10 lux, is most important 

 at low prey concentrations. For prey concentrations exceeding 6.8 cal/1 (= 

 1000 nauphi/1) winter flounder larvae could meet their daily food 

 requirements in less than 10 hours and at prey levels above 13.6 cal/1 (= 2000 

 nauplii/1) established feeders could meet requirements in only 5 hours. It is 

 apparent that the seasonal variation in day length and light intensity are 

 important elements in any model predicting survival offish larvae, particularly 

 in high latitudes where seasonal variation is greatest. 



Possible harmful effects of natural sunlight on larvae are poorly known. 

 Ultraviolet Ught near the sea surface may be deleterious to pelagic eggs (63). 

 Some information on effects of ultraviolet light on pelagic embryos may apply 

 to larval stages. Pommeranz (75) tested effects of ultraviolet light on plaice 

 embryos, using an artificial UV intensity of 0.05 ly/min ( i ly = 1 cal/cm ) at 

 the water surface of 350 ml incubators with a 200 ml/min water exchange. 

 Although results were not conclusive, lower percentages of embryos survived in 

 12 hours and 24 hour-exposed incubators than in control incubators which 

 were in the dark. Pommeranz (75) also exposed plaice embryos to natural 

 daylight, natural daylight with UV wavelengths filtered out, and natural 

 daylight with long wave infrared above 1400 nm filtered out. Average light 

 intensities in two experiments were 257 ly/day and 462 ly/day. Only the high 

 intensity experiment caused high mortality of embryos (35 percent). 

 Ultraviolet light was considered to be the lethal agent because corresponding 

 mortalities were not observed in incubators where ultraviolet was filtered out. 



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