![]() Oocytes at late stage 3 and early stage 4 can be distinguished based on the presence or absence of egg yolk bodies. ![]() Despite the freezing artefacts observed in late stage 3 to 4, the maturity level of DS oocytes could be accurately assessed from frozen Delta Smelt. Ruptured yolk bodies merged with each other or with the cytoplasm and lost their circular shape. Likewise, freezing disrupted the integrity of yolk bodies in stage 4 oocytes. Ruptured cortical alveoli formed a large mass of cortical alveolus at the center of the oocyte, dislocating the nucleus toward the periphery. Oocytes in late stage 3 have the most abundant cortical alve- oli that occupy a large area of the oocyte. However, cryopreserva- tion ruptured the cortical alveoli and egg yolk bodies in later oocyte stages. Flash-freezing did not alter the cellular morphology of oocytes at immature stages 1, 2 and early stage 3. These results suggest that flash-freezing whole fish and then preserving in formalin for histopathologic analysis can provide critical informa- tion regarding microscopic changes or lesions in Delta Smelt that may develop as an indicator of exposure to stressors as demon- strated in Hammock et al. 4B) and separation of ionocytes from the inter- stitial tissue at the base of the primary lamella (Fig. Despite the cellular changes or tis- sue artefacts arising from flash-freezing, the key histologic features were observed in frozen sections that allowed us to detect and to distinguish actual alterations such as intracytoplasmic vacuoles in mature oocytes (Fig. Flash-frozen tissues of Delta Smelt revealed good histologic characteristics in gill, gonad, and liver sections based on fundamental criteria, including (1) tissue architecture and integrity, (2) fixation quality, (3) cellular detail and resolution such as appear- ance of nuclei, nucleoli, and cell membranes, and (4) staining quality of tissues (Figs. One of the biggest challenges for utilizing flash-frozen tissues is the necessity for histopathologists to be familiarized on evaluat- ing and interpreting lesions and other microscopic changes from frozen samples. For example, formalin-fixed smelt are ideal spec- imens for evaluating histopathological changes but will no longer be useful for the analyses of enzymatic activities, pathogen iso- lation, otolith microchemistry, RNA/DNA ratio, and triglycerides. Although directly pre- serving the fish in fixative after collection provides standard tissues for histopathology, fixed tissues are no longer useful for the other measurements. Our study demonstrates the advantage of freezing smelt prior to fixation for histological analysis, improving its compatibility with analyses of other biomarkers and endpoints. Overall, we detected no difference in pathogen types and scores between fresh and frozen smelt samples. ![]() The absence of viral agents from parallel samples of fresh and frozen tissues of Delta Smelt indicates that viruses were not detectable in either tissue type. For viral isolation, the World Health Organization (2000) suggests preserving clinical specimens in liq- uid nitrogen or in −20 or −70 Our findings corroborate previous results in other fish species where common bacterial fish pathogens remained viable at 20-60 days post freezing (Brady and Vinitnantharat, 1990). ![]() More- over, our results showed that the bacteria that were recovered in frozen and fresh tissues of smelt were similar in terms of species type (present results Baxa et al., 2015). Under extenuating circumstances such as in field monitoring surveys, freezing samples can be used to preserve the integrity of fish tissues for isolation of microbial organisms (Noga, 1996 Klinger and Francis-Floyd, 2013). Bac- terial isolation was compared between fresh and frozen tissues as the standard method requires the use of fresh tissue samples (AFS-Fish Health Section, 2007). These results suggest that flash-freezing is an appropriate method for preserving field samples of Delta Smelt, (present results, Baxa et al., 2015) to minimize the deterioration of tissues for microbial isolation. Bacterial organisms were viable in frozen smelt tissues, and pathogen scores were similar between fresh and flash-frozen tissues. frozen tissues also demonstrated suitable outcomes for isolation of pathogens that commonly use fresh tissues.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |