The use of herbicides for agricultural and aquatic weed control has increased worldwide. These substances are potentially toxic pollutants because they induce the production of reactive oxygen species for biological systems and exert oxidative stress in nontarget organisms living in the treated aquatic systems. Recent evidence suggests differences in the toxicity of glyphosate in the form of an active ingredient compared to the toxicity of glyphosate in combination with surfactants, such as those found in commercial formulations. In Mexico, one of the most widely used glyphosate-based herbicides is Yerbimat, which has agricultural as well as aquatic weed control applications. However, there are no aquatic toxicity data, particularly regarding native fish. Therefore, we determined the acute toxicity of commercial-formulation Yerbimat in a static bioassay at 96 h (LC(50)). We also determined its toxicity at 96 h in sublethal concentrations to assess the lipid peroxidation levels (LPX), catalase activity, hepatic glycogen content, and histological damage in the liver and gills of the fish Goodea atripinnis associated with chronic exposure (75 days). The LC(50) was 38.95 ± 0.33 mg/L. The results of the short-term exposure study indicate that Yerbimat can potentially induce oxidative stress in G. atripinnis, because LPX was increased in the gills and liver. Catalase activity was reduced in the gills but increased in the liver, whereas hepatic glycogen was depleted. Chronic exposure was associated with histopathological damage in the gills and liver, some of which was irreversible. Yerbimat represents a potential risk for aquatic biota; therefore, we recommend that its application be carefully considered.

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The ovarian cycle was studied in Ameca splendens, a viviparous fish native to western Mexico. Two wild populations living in environments with differential conditions (a small pond adjacent to a reservoir and a spring) were examined to determine whether the conditions these populations are exposed to can elicit differences in the reproductive cycle. The two sites differ from each other with respect to several environmental factors: the spring has clear, oxygen-rich water while the pond has higher levels of conductivity, hardness and inorganic nitrogen. Six stages of gonadal maturation were identified in A. splendens, based on histological and macroscopic characteristics of the gonad. The relative frequency of gonadic stages at both sites showed two reproductive peaks during the year: from March to May and from September to November. Histologically, ovaries exhibit an asynchronous development in both populations, revealing the existence of a multiple reproductive cycle. Relative mean condition shows organisms are in peak condition (K > 1) at age class 1+ as they recruit to reproduction; K was <1 following the onset of multiple reproduction. The Fulton condition factor shows that the mean condition is slightly higher in the spring population. The relative frequency of gonadal maturation differed between the study sites and is indicative of the plasticity of A. splendens in facing different conditions within the environments it inhabits.

The endangered endemic fish Ameca splendens was surveyed monthly from June 200 1 to May 2002 at two sites in the upper Rio Aineca basin. Both populations demonstrated two annual reproduction peaks, with one in the spring season and the other in late fall. The condition and gonadosomatic index were higher in the population from the upstream pristine environment. Those fish in the pollutionstressed downstream region attained greater body length, longevity, and fecundity.

SUMMARY: This paper describes the oogenesis of Chiton virgulatus, based on histological observations under transmission and scanning electron microscopy. Three oocyte types were identified: i) previtellogenic oocytes with a mean diameter of 50±20.5 µm, surrounded by elongated follicular cells of approximately 5 µm, ii) immature vitellogenic oocytes with a mean diameter of 113±15.3 µm and small cytoplasmic projections denoting the onset of the oocyte hull development; adjacent to each projection are pores approximately 0.7 µm in diameter, and iii) mature vitellogenic oocytes with a mean diameter of 146±24.8 µm; the oocyte cytoplasmic projections grow and its apical zone becomes trident-shaped; follicular cells adopt a bulbous shape due to the growth of the elongation and can reach up to 20 µm in length. The morphology and ultrastructure of the projections of the mature vitellogenic oocyte, as well as the size of pores at their base, are specific to C. virgulatus; therefore, these features could be used in taxonomic or fertilization studies.