192 NATURAL SCIENCE [March 



water species, the occurrence of others being more or less accidental. 

 At the period of high Nile tlie lake receives numerous additions to 

 the numbers of its fresh-water species. Of the marine fauna, the 

 Mugils are the most abundant. Five species are found in the lake, 

 and two of these — viz., M. cephalus and M. capita — are of the highest 

 economic importance. They are taken at all seasons of the 

 year, though at certain periods more abundantly than in others, due 

 either to their local occurrence during the spawning season or to 

 certain conditions of the water. M. capito is more generally diffused 

 throughout the lake than the larger species, and it shows a greater 

 preference for fresh water than the latter, which in the adult stage 

 is always found near the deeper and salter localities. Neither of 

 them attain the maximum recorded size of their species. M. capito 

 is rarely found to exceed 40 cm. in length, and 58 cm. is about 

 the maximum for cephalus. This would appear partly to be the 

 result of overfishing, but observations show that in the case of 

 cephalus few spent individuals return to the lake after spawning is 

 over, and that nearly all the fish of the spawning shoals which leave 

 the lake are virgin fish. Older fish are to be found in the Suez 

 Canal, which has yielded individuals of over 84 cm. The spawning 

 season of M. cephalus lasts from May till the beginning of November, 

 a period which seems to be interrupted for from six to eight weeks 

 in the months of August and September when only a few scattered 

 spawners leave the lake for the sea. 3f. capita spawns from the 

 first week of November till about the end of December. They leave 

 the lake in shoals, which return empty after one day or two, then 

 after an interval, during which their reproductive organs fill again, 

 they migrate seawards a second time. At least two crops of ova 

 are ripened in a spawning season. 



As before mentioned, the grey mullets are used for the manu- 

 facture of fessikh, and they form on an average nine-tenths of the 

 total catch landed at the markets. 



Next in importance come Moronc labrax and M. orientalis. 

 They spawn from about the end of December till March, the season 

 of the smaller fish lasting the longer of the two. M. labrax is in 

 little evidence and orientalis not at all during the months of summer, 

 but from October till the end of the spawning season they are cauglit 

 in large numbers. 



Sciena aquila and Unihrina cirrhosa are found in the lake 

 throughout the year. They would appear to spawn sometime in 

 May or June, but no ripe specimens have been collected. 



Chrysophyrs aurata, which is found in the Salter parts of the 

 lake, leaves to spawn during the months of November, December and 

 January. 



The annual spawning migration of the common eel takes place 



