Genus Chirostoma belongs to Atherinopsidae family and it is an endemic species from the Mesa Central in Mexico. Abundance of its species have decreased and some ones have been placed on the threatened species list, because of overfishing, urbanization, industrialization, destruction, habitat fragmentation, pollution and exotic species introduction. Chirostoma jordani (Woolman, 1894) is a freshwater fish with biological, ecological, cultural, and commercial importance. It has a broad distribution in Lerma drainage, Durango and Mexico City. In this last locality, their populations, although small, still persist in Xochimilco Lake; it is necessary to implement biotechnologies for their conservation, because of these causes and their basic biology. The aim was to standardize a sperm cryopreservation protocol in C. jordani, to determine extender solution, cryoprotective agent type and concentration, equilibrium time, freezing and thawed rate to be applied in assisted reproduction and conservation of genus Chirostoma. Chirostoma jordani adult males were collected in Atlangatepec Dam, Tlaxcala State, Mexico, to fresh seminal evaluation and cryopreservation protocol standardization. Four cryoprotectants effect was evaluated: dimethylsulfoxide (DMSO), methanol (MeOH), ethylene glycol (EG), and glycerol (GL) at five concentrations: 2%, 6%, 10%, 14% and 16% v/v. Higher and lower DMSO and MeOH 10% and EG 14%, decreased post-thaw motility percentage. Both DMSO and MeOH 10% and EG 14% had the highest post-thaw motility percentages, 48.8 +/- 1.5%, 54.5 +/- 1.0% and 53.5 +/- 1.0%, at 15, 10, and 5 min equilibrium times, respectively, thawed at 40 degrees C. Chirostoma jordani sperm can be cryopreserved with both DMSO and MeOH 10%, and EG 14%. These ones can be used for assisted reproduction. GL was not efficient, since it presented a post-thaw motility percentage very low.

Pseudomonas fluorescens is a bacterium that has been identified as a significant pathogen in fish from the aquaculture industry. However, the clinical signs and changes caused by the disease have not been studied well yet. This study aimed to determine the survival, morphological, and histopathological changes in zebrafish (Danio rerio) in an experiment involving 180 fish (0.250 ± 0.05 g). The organisms were inoculated intraperitoneally at four bacterial concentrations 1.5 × 10⁶, 1.5 × 10⁷, 1.5 × 10⁸, and 1.5 × 10⁹ CFU mL⁻¹ with respective control groups. Results showed that cumulative mortality at 96 h post infection (hpi) was 0% (1.5 × 10⁶ CFU mL⁻¹), 0% (1.5 × 10⁷ CFU mL⁻¹), 6.66% (1.5 × 10⁸ CFU mL⁻¹), and 33.33% (1.5 × 10⁹ CFU mL⁻¹). The survival curves were not statistically different (p = 1.000). Corresponding to differences between clinical signs and concentrations for 24 hpi (p = 0.7576) there were no significant differences, for 48 hpi statistical differences were obtained (p = 0.0008), while for 72 hpi (p = 0.8922) and 96 hpi (p = 0.333) they were not observed. The predominant clinical signs were anorexia, lethargy, erratic swimming, and peritoneal haemorrhage. The acute septicemic clinical form was determined. Histological analyses showed that the gills, liver, and spleen were infected and had severe pathological alterations. These findings indicate that the zebrafish is susceptible to P. fluorescens infection.

Fisheries and Aquatic Sciences

Post-mortem fertilization is considered a technique in which semen is extracted from a dead male to fertilize the egg of a living female. Therefore, this technique can be an excellent option in the face of the loss of biodiversity of multiple animal species. The objective of this research is to implement post-mortem assisted reproduction in the charal, Chirostoma jordani, which is a species of economic, biological and cultural importance in Mexico. Mature males were obtained from commercial capture Atlangatepec Dam, Tlaxcala, Mexico. The mature males were sacrificed and divided into three groups: 1) room temperature 18±1°C, 2) ice 5±1°C and 3) refrigeration 11±1°C. The variables evaluated were: percentage (s), duration of motility (%), and fertilization rate (%) at zero, two, four, six, eight and ten hours in quadruplicate, respectively. The results indicate that sperm viability decreased over time; at room temperature it lasted six hours; in ice and refrigeration 10, denoting significant differences (P90 and ~80%, respectively) (P<0.05). For practical purposes, it was demonstrated that semen from post-mortem organisms can be used to develop conservation practices.

Chirostoma humboldtianum is an endemic atherinopsid from Mexico that has been of high socio-cultural and economic importance since pre-Hispanic times. It was the first ictic species from Mexico described for science, and it is considered the basal species that gave rise to a nominal group known as white fish or silversides. The aim of this research was to analyze semen quality in relation to breeding fish size and its effect on sperm cryopreservation during an annual cycle. Sexually mature males were collected from January to December 2023, in San Felix dam, Tiacaque, Mexico State, Mexico. The water temperature was measured, and the photoperiod was obtained from the Instituto Nacional de Geografía y Estadística (INEGI). Males were classified into two groups of total length (TL) after analyzing the variation in TL through a size histogram: (G1) 9–13 cm and (G2) longer than 13 cm. Semen volume (µL), sperm concentration (cells µL⁻¹), and motility percentage (%) were determined in all individuals of each group. Likewise, eight straws were cryopreserved per month per group, each one with 10 µL of semen from a mixture of three randomly selected individuals and cryopreserved at −196 °C for 72 h. The post-thawing motility percentage was subsequently verified. Males produce semen continuously all year round, with two periods of higher volume, March and June–August, defining two reproductive periods. The beginning of the first one coincides with the increase in water temperature, from 13 ± 2 to 18 °C. Males with a length more than 13 cm had a higher semen production compared to smaller males (17.33 ± 7.34 and 12.52 ± 4.41 µL, respectively, p < 0.05). The largest semen volumes were registered in March and from June to August in both groups. However, G2 males presented with a larger semen volume. Both groups had a marked decrease in a similar manner in April–May and September to January (p < 0.05). Sperm concentration was similar throughout the year in both groups (p > 0.05) (G1 = 1.35 ± 0.36 × 10⁶ µL⁻¹) (G2 = 1.31 ± 0.35 × 10⁶ µL⁻¹). In addition, fresh sperm motility was high in both groups (G1 = 96 ± 3%, G2 = 97 ± 4%) (p > 0.05). The highest sperm concentrations were observed in March to July, through to October for both groups (p > 0.05), while post-thaw sperm motility decreased by about 50% (G1 = 45 ± 4%) (G2 = 46 ± 6%) during the annual cycle (p > 0.05). The largest post-thaw motility was observed in March and from July to September in G1 and in March and from June to October in G2. Analysis of semen quality throughout the annual cycle reveals aspects of the reproductive biology of C. humboldtianum, including two reproductive peaks and continuous semen production.

La reproducción en peces está regulada por factores ambientales, sociales y químicos, aunado a cambios constantes en la temperatura del agua, variables que tienen una gran importancia en la producción y liberación de hormonas y feromonas reproductivas. Los peces se han adaptado a la época más favorable de su estrategia reproductiva. Pero, ¿cómo perciben los factores ambientales los peces? ¿Cómo se sincronizan los machos y las hembras para el desove simultáneo? Este artículo tiene como propósito comprender cómo los peces captan los factores ambientales y cómo los traducen para poder reproducirse, información importante para optimizar la reproducción y conservación in situ, en centros acuícolas o de investigación.