FIELD STUDIES ON THE EFFECT OF THE FISHES OREOCHROMIS NILOTICUS AND HAPLOCHROMIS DESFONTAINESI ON VECTOR SNAILS IN EARTHEN FISH PONDS AND NATURAL HABITAT IN EGYPT

Field studies were conducted at 7 earthen fish ponds (fish
hatchery at Al-Abbassa, Sharkia Governorate) used for breeding the
fish Oreochromis niloticus to survey both vector and non vector snails
in fish ponds and to determine the efficiency of fish against snail
vectors. The results indicated that snails belonged to eight species, in
descending order: Bellamya unicolor (51.3%) > Physa acuta (25.3%)>
Gabbialla senaariesis (10.3%)> Cleopatra bulimoides (4.9%)>
Bulinus truncatus (3.3%)> Lansists carinatus (1.9%)> Melanoides
tuberculate (1.9%)> Lymnaea cailliaudi (1.1%). Ponds which
contained young fish accommodated higher snails diversity than those
contained parent fish. Also, stomachs of specimens of O. niloticus
collected from fish ponds were examined for the purpose of studying
their food with emphasis given to vector snails. Results of the index of
relative importance (I.R.I.) emphasized the importance of artificial
fish food as a major food resource (8090.3) followed by snails (3880)
and then insects (382.3). Seasonal variation in the composition of the
diet showed that snail shell parts were the major food category in the
diet during summer (43%), and reached the lowest level during winter
(2%). In contrast, the artificial fish food was recorded as the highest
proportion in the diet during winter (58%) decreased remarkably
during spring (33%) and summer (35%) but increased again in autumn
(56%). In addition, stomachs of the fish specimens of Haplochromis
desfontainesi and O. niloticus collected from Ismailia irrigation canal
FIELD STUDIES ON THE EFFECT OF THE FISHES940
were examined to investigate the nature of the diet with emphasis
given to vector snails. Results of the I.R.I. indicated that snails were
the second important food items in the diet of both species. Snails
were present in the diet of H. desfontainesi in all seasons; however,
they exhibited marked seasonal variation in abundance with maximum
level during spring. They reached the highest level in the diet of O.
niloticus also during spring decreased during summer and remained at
the same level during autumn until disappeared in winter.