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The protozoan Perkinsus marinus was identified for the first time in the oyster Crassostrea corteziensis from the state of Baja California Sur, Mexico. Intensities of P. marinus infections increased from 0.5-2 to 2-5 (Machin scale) when water temperature was experimentally increased to 26[degrees]C for 15 days. Although disease-induced mortalities have not been reported in natural populations of C. corteziensis, high injected doses of P. marinus caused mortalities among experimental oysters. To evaluate the response of C. corteziensis with increasing levels of P. marinus, expression levels were investigated for genes involved in phagocytosis, cellular proliferation, apoptosis, and inhibitors of serine proteases. Oysters with low infection showed higher gene expression of the serine protease inhibitor gene, as well as of genes involved in phagocytosis (nicotinamide adenine dinucleotide phosphate-oxidase, actin, superoxide dismutase, and glutathione s-transferase), and genes involved in apoptosis and DNA fragmentation (tumor necrosis factor and caspase-8). Results of observed mortalities associated with high intensities of P. marinus infection indicated that C. corteziensis is a susceptible host to this pathogen. Phagocytosis and cell death by apoptosis were higher in less-infected oysters, as an apparent result of the increased expression of apoptosis-related genes. KEY WORDS: gene expression, Perkinsus marinus, oyster disease, apoptosis, phagocytosis, Crassostrea corteziensis, INTRODUCTION Cultivation of the normative Pacific oyster Crassostrea gigas (Thunberg, 1793) along the northwestern coast of Mexico has resulted in unexplained mortalities in areas where summer temperatures reach 35[degrees]C, unlike [...]

Agave lechuguilla is a succulent plant species, mainly distributed in the northeast of Mexico and south of the United States of America. The main use for this plant is the fibre´s extraction (known as Tampico fibres), resulting in 15% of fibres and 85% of a by‐product waste named guishe. The lechuguilla collectors, normally incinerate the guishe, thus causing environmental contamination. Interestingly, recent studies showed that guishe contains molecules with nutritional properties, such as saponins, flavonoids and sugars. Therefore, in this work, we evaluated the effect of the crude extract of guishe as a feed additive in whiteleg shrimp diets. According to that, MS‐HPLC analysis of the extract showed the presence of saponins such as diosgenin, smilagenin, hecogenin, manogenin, tigogenin hexose, yucagenin, chlorogenin, diosgenin diglucoside and the flavonol, quercetin. After chemical analysis, the crude extract was included into an experimental diet in four levels; 0% (L0%), 0.1% (L0.1%), 0.3% (L0.3%) and 0.6% (L0.6%). Dietary incorporation of the extract was evaluated by zootechnical performance, haemolymph biochemistry, histomorphology and digestive enzyme activity of shrimps. After 5‐week feeding, the L0.3% diet showed significantly higher growth and better feed utilization among treatments. A significant increase in tubule epithelium height and tubule coverage area from hepatopancreas in shrimp under L0.3% diet compared with the control diet suggest an improvement of the health and nutritional status of the shrimp. Inclusion of L0.3% and L0.6% of the crude extract resulted in a reduction in amylase activity, without effect in glucose levels in the haemolymph. Thus, we suggest that lechuguilla guishe crude extract contains nutritional molecules that may be used as a feed additive to promote shrimp productivity. [ABSTRACT FROM AUTHOR]