Effect of temperature on hatching and growth of cuban gar (Atractosteus tristoechus) larvae
Hatching success, growth, development and survival of Cuban gar ( Atractosteus tristoechus ) larvae were examined at different temperatures (26, 28 and 30 o C) up to 18 days after hatching (DAH). The time to hatching was inversely related to the incubation temperature (87, 100 and 111 h). Larval survival at the time of hatching was significantly lower at 30 o C (50.3 %), coinciding with the highest larval mortality (30.2 %). Growth rates were 1.75 mmd -1 -10.4 % d -1 at 26 o C,1.30 mm d -1 -10.2 % d -1 -1 at 28 o C and 1.40 mm d -1 -10 % d -1 at 30 o C. Three similar critical periods were identified: 0-6, 7-11 and 12-18 DAH. During the first period, a similar increase in weight and a significant increase in total length occurred, mainly at 30 o C, indicating a more efficient reconversion of the yolk reserves. Later, growth was equally slow, corresponding with the transitional period from endogenous to exogenous feeding, indicating a similar physiologic pattern regardless of incubation temperature. Weight and length increased during the last period, with the greatest increase at 26 o C in contrast with the lowest gain at 30 o C. The inflexion points of many morphometric characters and the developmental stages accelerated with the increasing temperature. Although it was impossible to determine the optimal temperature, it was evident that 26 o C favored hatching success and larval growth.
Preparation of a fish embryo for micromanipulation: staging of development, removal of the chorion and traceability of PGCs in Prochilodus lineatus.
The transplantation of primordial germ cells (PGCs) is a valuable tool for gene-banking and reconstitution by means of a germline chimera. For this technology, studies regarding developmental stages and traceability of PGCs are necessary. The objective of this study was to develop a micromanipulation procedure for the future establishment of cryobanks of PGCs in migratory characins. Incubation temperatures were evaluated at 22 ° C, 26 ° C, and 30 ° C in order to synchronize developmental stages. The highest hatching rates and the lowest abnormality rate arose at 26° C, which was considered to be the best incubation temperature. Enzymatic removal of the chorion was determined to be best using 0.05% pronase, in which the embryos presented better survival rates. In order to visualize PGCs in vivo, artificial GFP-nos1 3'UTR mRNA was injected and the migration route was observed in vivo as PGCs were visualized firstly at the segmentation stage (6 to 13 somites). The number of GFP positive cells ranged from 8 to 20 per embryo (mean of 13.8; n = 5). After hatching, GFP-positive cells increased to 14 to 27 embryos (mean of 19.8; n = 5). Visualization of the GFP-positive cells was possible at 10 days post hatching, and at this stage, the cells were positioned in the yolk extension region. This is the first report on PGC visualization in vivo in Neotropical fish; the obtained data provide information on the identification and migration of PGCs. The information presented in this work brings new insights in gene banking in Neotropical species and subsequent reconstitution through a germinal germline chimera.
Heritage Languages: In the 'Wild' and in the Classroom
Heritage speakers are people raised in a home where one language is spoken who subsequently switch to another dominant language. The version of the home language that they have not completely acquired – heritage language – has only recently been given the attention it deserves from linguists and language instructors. Despite the appearance of great variation among heritage speakers, they fall along a continuum based upon the speakers’ distance from the baseline language. Such a continuum-based model enables researchers and instructors to classify heritage speakers more accurately and readily. This article discusses the results of research on lower-proficiency speakers, identifying recurrent features of heritage languages in phonology, morphology, and syntax. Preliminary results indicate that different heritage languages share a number of structural similarities; this finding is important for the understanding of general processes involved in language acquisition. The article also presents implications of the main findings for language education and identifies areas needing further study.