of the drainage is needed Rio Aguacatan was exami 
j e ned below the spring and t f 
Aguacatan, The stream is large, and contains an abundance of sai the eat mine Ny 
ateeper than five meters per kilometer, and fi 
Although the temperature is 15 to 17 de ish foods occur in only moderate amounts. 
they would have to be stocked anmally, for silt 
would not be conducive to successful a a Be ing and rather uniformly high temperature 
Inland Lakes 
Laguna de Amatitlan 
Laguna de Amatitldn is located on the Pacific slope 28 kilometers so 
Guatemala City at an altitude of 1,245 meters. The sha ea width of the Pica scans 
five kilometers; its length, about 13. It is divided into two basins by a railroad fill 
about 1,400 meters in length. The upper basin contains about six square kilometers, the 
lower about eleven, making a total of approximately 1,724 hectares. The greatest depth in 
the upper basin is 28 meters; and in the lower, 34. ‘The benches or shallow inshore areas 
usually are not more than 10 to 15 meters wide, averaging about 12; and they extend to a 
depth of approximately 6 meters. Beyond the bench » the water increases rapidly in depth 
and that part of the lake is utilized little by the present fish population. Nearly all of 
the northwest shore of the lower basin is steep, and the water reaches a depth of 10 to 20 
meters or more at a distance of only four or five meters from shore. The botton slopes 
more gently along the south shore, the rocky bench area extending 5 to 20 meters in width. 
The entire northeast shore and the upper basin have beds of tules (Typha and Scirpus) 
averaging 15 meters in width and extending out to depths of about two meters. There are 
also beds of Potamogeton, Ceratophyllum, and Chara growing in the tule beds » and often 
extending out to depths of six or more meters. 
The fishes found in Laguna de Amatitldn were the pepesca (Astyanax), pescadito 
@oecilistes), pupo (Mollienisia), serica (Cichlasoma nigrofasciatum) » Mojarra (C. guttulatum), 
and the guapote (C. motaguense ). The pepescas, pescaditos, pupos, and sericas are all small 
fishes, usually reaching 3 to 15 centimeters in length. ‘They are abundant in the shallow 
areas of the lake, along the beaches, and amongst the vegetation. The mojarra (C. guttulatum) 
is not common. It occurred in our seine and gill-net catches in the ratio of 1 mojarra to 
70 guapotes. 
Before the introduction of the guapote about 1934, the mojarra (C. guttulatum) was 
the only fish of usable size in the lake, and it was esteemed as a food fish. The intro- 
duction of the guapote is said to have increased the take of food fishes. Since the 
guapote is a more generalized feeder, the mojarra was not able to compete successfully with 
it. Stomachs of the mojarra contained large quantities of vegetation, mud, and some animal 
remains, while those of the guapote contained crustacea, principally Amphipoda, and small 
fishes, insects, et cetera, with some vegetation and mid. These two fishes occupy the 
bench areas of the lake, and were not taken in water deeper than about six meters. The best 
catches were made at depths of two or three meters. The largest guapote ever caught in 
Laguna de Amatitlan was said to be 42 centimeters long, weighing 1.9 kilograms. They 
usually do not exceed a weight of one kilogram, and the average is more nearly one-half 
kilogram. 
Chemical Data.--The upper basin was examined at 11:00 a.m., March 9, 1946. The 
temperature of the air was 20 degrees Centigrade; the surface water, 23.3; and the bottom 
(15 meters) 22.3. Identical temperatures prevailed on March 15, 1947, at 10:00 a.n., 
Juday (1915), on February 5, 1910, found temperatures of 20 degrees at the surface and at 
10 meters; 19.8 at 15 meters; and 19.6 at 20 and 34 meters in depth. At 5 meters, the water 
contained 6.8 parts per million of oxygen; and at 15 meters, 5.2 parts per million. On 
March 9, 1946, the Secchi disk (20 centimeters in diameter) disappeared at 3.04 meters; the 
phenolphthalein alkalinity was zeros; the methyl orange alkalinity was 174 parts per million; 
and the pH, 8.l. 
107 
