Removal of the chorion before hatching results in increased movement and accelerated growth in rainbow trout (Oncorhynchus mykiss)embryos

Abstract

SUMMARY We investigated the effects of the chorion on movement and growth in rainbow trout (Oncorhynchus mykiss) embryos. To test if the chorion restricts movement and growth before hatching, we manually removed the chorion 3–6 days before the natural time of hatching (dechorionated) and compared movement, growth and oxygen consumption in dechorionated embryos and in embryos whose chorions remained intact until the time of hatching(chorionated). Dechorionated embryos exhibited 36 times more movement before hatching compared with intact embryos. By 10 h post-hatch there was no difference in the number of movements between the two groups. At the time of hatching [30 days post-fertilization (d.p.f.)], dechorionated embryos had a significantly greater embryonic body dry mass compared with chorionated embryos, which persisted up to 45 d.p.f. At first feeding (50 d.p.f.) there was no significant difference in embryonic body dry mass between the two groups. Dechorionated embryos had a significantly greater embryonic body protein content after hatching (32, 33 d.p.f.) compared with chorionated embryos. Despite the differences in movement and growth, there were no significant differences in oxygen consumption between chorionated and dechorionated embryos. Furthermore, there was no correlation between the number of movements and oxygen consumption in rainbow trout embryos(chorionated, dechorionated, and hatched). Taken together, the data indicate that rainbow trout embryos have the capacity to be relatively active before hatching, but that the chorion restricts or inhibits movement. Moreover,precocious activity in pre-hatch embryos is correlated with accelerated growth and higher protein content, suggesting that the exercise training effect observed in adult salmonids is also present in early developmental stages.

Parameters influencing the dissolved oxygen in the boundary layer of rainbow trout (Oncorhynchus mykiss) embryos and larvae

“…Amphibian and snail embryos have a relatively large perivitelline space compared with the trout embryo, where the yolk and body of the embryo occupy over 95% of the space inside the chorion (C. Ciuhandu, personal observation). In the present study, the small space inside the chorion of trout embryos probably limits whole body movements, in agreement with Ninness et al (Ninness et al, 2006). Pectoral fin flutter has been described in Atlantic salmon as alternatively abducting and adducting the fin (Peterson et al, 1991), therefore a faster moving smaller structure might function well in stirring the pvf when space inside the chorion is limited.…”

“…Previous studies on fish reported similar patterns of body movements throughout development (Peterson and Martin-Robichaud, 1983;Ninness et al, 2006). Therefore, the musculoskeletal system is sufficiently developed for high levels of activity soon after hatching.…”

“…Salmonid embryos and larvae are believed to be oxygen conformers at low oxygen concentration (see above); therefore, their metabolic rate depends on the available oxygen (Rombough, 1988a). The anaerobic capacity of salmonid embryos is very limited and could only play a very minor role at these life stages (Ninness et al, 2006).…”

Fish embryos on land: terrestrial embryo deposition lowers oxygen uptake without altering growth or survival in the amphibious fishKryptolebias marmoratus

“…Terrestrial red-eyed treefrog (Agalychnis callidryas) embryos move their bodies to reduce boundary layers and mix perivitelline fluid, thereby increasing oxygen availability and supporting a higher metabolic rate (Warkentin et al, 2005). Embryonic movement of fully aquatic rainbow trout (Oncorhynchus mykiss) embryos also increased prior to hatching, possibly as a strategy to enhance oxygen transport by mixing the perivitelline fluid within the chorion to dispel boundary layers (Ninness et al, 2006). Thus, although there is evidence that embryos are typically oxygen conformers, there may be environmental situations where embryos regulate oxygen diffusion by increasing movement within the chorion.…”

The effect of hatching time on the bioenergetics of northern pike (Esox lucius) larvae from a single egg batch during the endogenous feeding period

“…In fact, Green et al (2006) observed in anemonefish Amphiprion melanopus that small size embryos measured for total length 2 h after fertilization develop into small larvae at the time of hatching. Given that a smaller embryo body size may facilitate movement inside the egg capsule (Ciuhandu et al 2005;Ninness et al 2006), it is possible that the precocious hatch of some pike larvae at a smaller size is a result of intensified metabolism and increased oxygen demand of these embryos which triggers an escape from egg capsules (Miller and Kendall 2009). No significant differences in energy content of the entire larvae (Fig.…”