For most freshwater fish species, the fertilization process is external in an aquatic environment that promotes sperm activation and allows sperm to enter the micropyle. However, to be efficient, it’s essential that sperm movement, integrity and morphology are suitable with normal standards to promote fertilization. This is more evident in endangered species, such as the endemic species in Paraiba do Sul river basin, Steindachneridion parahybae, where the population of wild animals kept in captivity is less than 100 individuals. In that regard, the aim was to evaluate the effect of sperm characteristics on the quality of eggs and larvae of S. parahybae.
Gametes from 17 breeders were used, two females (2,225±247g) and 15 males (873±562g). The oocytes (175g) from the two females were homogenized and fertilized separately with the semen of the 15 males. Before fertilization, sperm concentration was evaluated (1.48x1010±0.58x1010 sperm mL-1), with the aim of applying the same inseminating dose (30,000 sperm, oocyte-1) to all males. For the semen from each male, three replicates were used (45 experimental units). An incubator (1.5L) containing 1g of oocytes (271±6 oocytes) was considered as an experimental unit. The sperm quality parameters evaluated were: Sperm survival (fluorescence method) (eosin-nigrosin method), rates of morphological changes, seminal plasma osmolality, sperm motility - MOT), sperm velocity (curvilinear - VCL, average path - VAP and straight line - VSL), straightness - STR, wobble - WOB, progression - PROG and beat cross Frequency - BCF. The quality parameters of the oocytes and larvae evaluated were: fertilization rates, hatching, normal larvae and hatching time. The evaluated sperm parameters were subjected to Pearson’s linear correlation analysis at a 5% level of significance between the oocyte quality parameters.
Only a significant positive correlation (r=0.60) was observed between the percentage of normal larvae and seminal plasma osmolality (P<0.05). The rest of the sperm parameters did not show a significant correlation (P>0.05) with the female parameters. Sperm motility can be represented by the non-linear equation Mot=100/(1-(-0.0272)*exp(0.1228*time). Sperm parameters obtained with CASA showed strong linear correlations (Pearson) and can be summarized by principal component analysis (PCA) summarized in two axes: Axis 1 (PCA1) represented 82.3% of the total variability and was negatively correlated with MOT, VCL, VAP, VSL, WOB and PROG and positively with BCF; Axis 2 (PCA2) represented 13.1% of the total variability and was positively correlated with STR. Additionally, the multi-response permutation procedure (MRPP) was efficient to evaluate post-activation time variability, indicating better sperm quality immediately after activation. It concludes that the osmolality of seminal plasma can be considered as an indicator of the efficiency of normal larvae for the S. parahybae, with semen with higher osmolalities promoting a greater number of normal larvae.
Acknowledgements: São Paulo State Research Support Foundation (FAPESP) nº 2012/07083-3