Prevalence of Gregarines and their relationship with water and soil quality in Penaeus vannamei aquaculture systems on Puná Island, Ecuador

Abstract

Shrimp farming presents several health challenges, including parasitic diseases, notably gregarines,
endoparasites of the gastrointestinal tract of invertebrates such as mollusks, annelids, and crustaceans.
Although gregarines are not considered highly pathogenic, their specificity to Penaeus vannamei makes
them opportunistic parasites of parasitic importance, playing a significant role in the health dynamics of
shrimp farms. Therefore, the objective of this study was to determine the prevalence of gregarines and their
relationship with water and soil quality in P. vannamei cultures on Puna Island, using microscopy and analysis
of physicochemical parameters. The study focused on an aquaculture farm under a semi-intensive production
system, in which three ponds under similar cultivation conditions were selected and designated P44, P46, and
P48. Water, soil, and shrimp samples were collected throughout a production cycle, and a total of 240 shrimp
were analyzed. Gregarines were observed in the gametocyte and syzygy stages of the intestinal contents of
the analyzed shrimp. P48 showed the highest gregarine infestation, followed by P46 and P44. The prevalence
of the parasitosis caused by the protozoan ranged from 57.50% (P46) to 61.25% (P44), while P48 showed a
value of 60.00%. The physicochemical parameters of the water did not show significant differences for any of
the analyzed variables, while, with respect to soil quality parameters, only organic carbon showed statistical
significance (p = 0.048). Likewise, strong positive correlations were observed between prevalence, intensity,
average abundance and organic carbon (r= 0.808, 0.915, 0.902, 0.907), demonstrating a close relationship
between these infestation indicators.