International Journal of Marine Science, 2017, Vol.7, No.24, 229-246
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aquacultures from the central west, southwest and southern regions where the main fish species in production are
gilthead seabream and seabass (
Dicentracthus labrax
L.). Fish are usually introduced into production ponds in
April, and captured in the following year, during summer. The growing period of gilthead seabream takes about 15
months. Infestations of the gilthead seabream by the gill parasite
A. ocellatum
may occur, particularly during
summer. Noga and Levy (1995) suggested that at the end of thegrowing season, when the water temperature
increases within production ponds, the proliferation of the ectoparasite and the damage done to the developing
fish can rapidly reach devastating proportions in terms of fish production. Low oxygen tension in the Salton Sea
in the summer months may reinforce the negative impact of
Amyloodinium ocellatum
. The shortage of external
oxygen, together with destructive alterations of the respiratory organs and distortion of epithelia1 tissues caused
by parasitic trophonts may depress the respiratory functions of fish. The likelihood of death by suffocation is
especially great for young fish heavily infected by parasitic trophonts. In this case, not only gas exchange in the
gills but also cutaneous respiration as a main source of oxygen for these fish (Rombough and Ure, 1990) may
have been reduced. Alterations in the water-salt balance processes in the damaged gills were also suspected to
occur (Bonga, 1997). The developing immune system of such young fish may not be able to fight off infection
successfully. The present study to explain the occurrences per season of
A. ocellatum
in cultivated European
seabass. Out of the examined 1065
Dicentrarchuslabrax
fish, 618 (58.02%) were found to be infested with
Amyloodinium ocellatum
. The highest rate of infestation was recorded during spring season with aprevalence
(90.10%) while the lowest was during winter season with aprevalence (30.76%). Khan and Thulin (1991)
mentioned that, environmental factors can strongly promote infestation of fish by external parasites In the Salton
Sea,
A. ocellatum
infestation of young tilapias increased under unfavorable environmental conditions of the lake.
The severity of fish infestation by
A. ocellatum
was determined by an interaction by te pathogen with abiotic
variables, such as water temperature, salinity, oxygen concentration and nitrogen level. Kuperman and Matey
(1999) suggested that the occurrence of
A. ocellatum
in fish gills is associated with specific variances in
environmental variables such as temperature and salinity. A correlation study with environmental and biological
factors as variables the occurrences of
A. ocellatum
in cultivated gilthead seabream) is conducted by Pereira et al.
(2010). The study concludes that salinity is positively related with trophont occurrences. Dissolved oxygen, water
temperature, pH, and phytoplankton biomass have significant negative relationship with
A. ocellatum
trophonts.
Pereira et al. (2010) is conducted the correlation study with environmental and biological factors as variables to
explain the occurrences of
A. ocellatum
in cultivated gilthead seabream.
Salinity is positively related with trophont occurrences. Dissolved oxygen, water temperature and pH, have
significant negative relationship with
A. ocellatum
trophonts. California Regional Water Quality Control Board
(1994) found that, the parasitic dinoflagellate
Amyloodinium ocellatum
appears to be as an important factor
affecting survival of fish populations in the Salton Sea. The parasite infestation of young tilapia increased under
unfavorable conditions at the lake. The massive fish mortality events often reported at the Salton Sea may be the
result of synergistic effects of parasite load and a complex set of environmental stressors. Salinity is the only
environmental variable positively correlated with
A. ocellatum
trophonts, having an important role in parasite
occurrences that is also supported, in part, by Kuperman and Matey (1999), who pointed out that a combination of
high water temperature and high salinity levels promoted heavy infestation by
A. ocellatum
. Thus, the present
study attempts to correlate environmental factors with
A. ocellatum
, occurrences in cultivated European seabass.
The present study concluded that there was direct strong significant correlation between pH levels and parasitic
infestation. Also, there was astrong significant correlation between Salinity levels and parasitic infestation. There
was a weak significant correlation between ammonia levels and parasitic infestation. Also, there was a significant
correlation between water temperature levels and parasitic infestation while there was no significant correlation
between dissolved oxygen and
A. ocellatum
Occurrences. Montgomery-Brock et al. (2001) reported that,
Treatment with hydrogen peroxide to 75-150 mg/L was effective in eliminating trophontes in
Polydactylus
sexfilis.
