Embryonic development of the grass pufferfish (Takifugu niphobles): From egg to larvae

Gluconeogenesis during development of the grass puffer (Takifugu niphobles)

During the development of teleost fish, the sole nutrient source is the egg yolk. The yolk consists mostly of proteins and lipids, with only trace amounts of carbohydrates such as glycogen and glucose. However, past evidence in some fishes showed transient increase in glucose during development, which may have supported the development of the embryos. Recently, we found in zebrafish that the yolk syncytial layer (YSL), an extraembryonic tissue surrounding the yolk, undergoes gluconeogenesis. However, in other teleost species, the knowledge on such gluconeogenic functions during early development is lacking. In this study, we used a marine fish, the grass puffer (Takifugu niphobles) and assessed possible gluconeogenic functions of their YSL, to understand the difference or shared features of gluconeogenesis between these species. A liquid chromatography (LC) / mass spectrometry (MS) analysis revealed that glucose and glycogen content significantly increased in the grass puffer during development. Subsequent real-time PCR results showed that most of the genes involved in gluconeogenesis increased in segmentation stages and/or during hatching. Among these genes, many were expressed in the YSL and liver, as shown by in situ hybridization analysis. In addition, glycogen immunostaining revealed that this carbohydrate source was accumulated in many tissues at segmentation stage but exclusively in the liver in hatched individuals. Taken together, these results suggest that developing grass puffer undergoes gluconeogenesis and glycogen synthesis during development, and that gluconeogenic activity is shared in YSL of zebrafish and grass puffer.

Embryonic development of the bullseye puffer Sphoeroides annulatus (Tetraodontidae): A morphofunctional approach to ontogenetic steps

The embryonic development of the bullseye puffer, Sphoeroides annulatus, was characterized on the basis of the theory of saltatory ontogeny. This theory predicts a correlative relationship between the ontogeny-type in an altricial-precocial spectrum and the habitat that a species occupies within an unstable-stable environmental spectrum. Because S. annulatus inhabits a variety of unstable environments along a wide latitudinal range, the hypothesis that this species presents one of the most altricial embryonic developments among tetraodontids was tested. Based on major developmental events that marked the ontogenetic thresholds nine embryonic steps were identified. Developmental features such as small adhesives eggs, lack of vitelline circulation, small free embryos swimming up at hatching guided by positive phototaxis, and small first-feeding larvae actively swam in the water column, suggest that S. annulatus belongs to the reproductive guild of the nonguarders-lithopelagophils. Moreover, a comparative analysis of the developmental sequences, egg size, and first-feeding larvae size between tetraodontids confirms the hypothesis of this study and supports the evolutionary principle of the altricial-precocial spectrum postulated in the theory of saltatory ontogeny.

Hormonal induction of ovulation using Ovaprim™ [(D-Arg6, Pro9NEt)-sGnRH+domperidone] and its impact on embryonic development of wild-caught Longspine scraper, Capoeta trutta (Heckel, 1843)

Knowledge of gamete quality is a prerequisite for developing techniques to fertilize eggs and rear offspring for hatchery production. Our objective was to develop assisted reproductive techniques, via hormonal induction of final oocyte maturation (FOM), for Longspine scraper, Capoeta trutta. Fish were administered injections of salmon gonadotropin-releasing hormone analogue containing anti-dopaminergic drug (Ovaprim™) or saline (control). Effects of Ovaprim on induction of ovulation, gamete quality, embryonic development, and larval survival were later examined with serum steroid hormone levels and ovarian histology. The saline group failed to spawn, whereas Ovaprim accelerated FOM and induced spawning. Fish treated with Ovaprim showed an increase in gonadosomatic index, egg diameter, and wet weight relative to controls. Average absolute fecundity, relative fecundity, fertilization, and hatching rates were 8823 eggs/spawn, 53 eggs/g body weight, 95%, and 91%, respectively. Serum 17α,20β-dihydroxy-4-pregnen-3-one (DHP) levels were significantly enhanced by ∼4-fold in Ovaprim-treated fish compared to the saline-injected fish, while 17β-estradiol levels declined upon FOM in hormone treated fish. Embryonic development closely resembled the teleost scheme, despite variations in timing. Larval survival at 6 and 12days post-hatch were 98% and 95%, respectively. Results suggest that Ovaprim is efficient for inducing spawning in C. trutta for stock enhancement or hatchery purposes.