Pajjers in Marine Biology and Oceanography, Suppl. to vol. 3 of Deep-Sea Research, pp. 250-256. 



The production of Liza ramada (Risso) in Lake Mariut, Egypt 



By R. S. WiMPENNY 



Fisheries Laboratory, Lowestoft, England 



Summary — The production of the grey mullet Liza ramada in Lake Mariut, Egypt, is followed from 

 its introduction in 1920 until 1935, special attention being paid to the years 1928-31 and 1933, when 

 age censuses were available. 



After an initial build-up to a steady state between 1923 and 1926, it is thought that a decline set 

 in about 1927-8 due to a lowering of the lake-level, and that this ended in lower levels of the popula- 

 tion from 1930 to 1933 and a further fall in 1934 and 1935. The decline in numbers estimated in the 

 O group catch represented a heavy mortality in the first year, and it is thought that this occurred very 

 soon after the fry were introduced into the lake, as the rate of growth of fish caught in their first year 

 in the lake showed no fall, but a slight increase between 1928 and 1933. 



On the delta coast of Egypt there are several large and extremely shallow lakes 

 usually connected with the sea during the whole or a part of the year by shallow 

 channels. They are of great fertility, 60-270 kgm per hectare compared with 100 to 

 400 kgm per hectare for cultivated carp ponds in Germany, and 5 to 250 kgm per 

 hectare for cattle on grassland (Mortimer, 1954). Among the species that go to make 

 up the yield are those of the genus Tilapia which can give over 9,000 kgm per hectare 

 in the fertilized ponds of the Belgian Congo (Mortimer, 1954) and the grey mullets, 

 a species of which constitutes 50-60% of a yield of 1,500-4,000 kgm per hectare for 

 the brackish ponds in the New Territory of Hong Kong (Bromhall, 1954). It is one 

 of the most important species of this latter group, Liza ramada (Risso) formerly 

 called Mugil capita Cuv. and known locally as the " Tobar " which is the subject of 

 this contribution. 



The habit of the Tobar is to enter the lakes from the sea in great numbers between 

 January and April. During this time it will be found to increase in modal size from 

 16 to 20 cm during the course of the run. The fry which enter the lakes already 

 possess scales, the gut is short and simple and both animal and vegetable plankton is 

 eaten. Subsequent growth is rapid and the intestine becomes lengthened and con- 

 voluted as the fish changes its feeding habits to that of a mainly vegetarian browser. 



The length range of the commercially caught population is from 14-30 cm long and 

 the average size, which also happens to be near that at which both sexes may first 

 be commonly found mature, can be taken as 20 cm. Growth to the end of the first 

 year (" O group ") appears to vary a good deal and fish may be from 14-20 cm, 

 indeed in exceptional circumstances in fresh water ponds 28 cm has been reached in 

 this time. In the second year (" I group ") length can increase by from 1 to 6 cm, and 

 in the third (" II group ") 1 or 2 cm. Generally, however, there appears to be little 

 growth after maturity has been reached. 



When in October and November sexually mature fish leave for the sea in large 

 shoals, most of these are at the end of their second year. Spawning must take place 

 in the immediate coastal belt, as no record is known of any individual of this species 

 being caught in the trawl, or by any other method of fishing employed outside the 

 littoral zone. Although I was fortunate enough to find and describe the planktonic 



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