Effect of temperature on viability and axial muscle development in embryos and yolk sac larvae of the Northeast Arctic cod (Gadus morhua) |
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Authors: | T F Galloway E Kjørsvik H Kryvi |
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Institution: | Norwegian University of Science and Technology, Department of Zoology, Bratt?ra Research Centre, N-7034 Trondheim, Norway, NO University of Bergen, Department of Zoology, Allègt. 41, N-5007 Bergen, Norway, NO
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Abstract: | Cod (Gadus morhua L.) eggs may develop and hatch within temperatures of −1.5 to 12 °C, but little is known about the effects of very low temperatures
on larval characteristics. Eggs of the Northeast Arctic cod (Gadus morhua) were incubated at 1, 5 or 8 °C from Day 1 after fertilisation until hatching, and transferred to 5 °C after hatching. Histological
samples of the axial musculature were taken at hatching and 5 d after hatching, and the data on muscle cellularity from these
samples were related to survival and hatching, size, developmental data and viability of the yolk sac larvae. All larvae hatched
at the same developmental stage. Incubation of eggs at 1 °C produced shorter larvae with a larger yolk sac and more, small
deep fibres at hatching than larvae from eggs incubated at 5 or 8 °C. The larval size difference was still present 5 d after
hatching, a time at which the larvae from 1 °C-incubated eggs were less developed and less resistant to an acute viability
stress test (65 ppt salinity). Although there were no differences between temperature groups in number and size of muscle
fibres 5 d after hatching, the deep fibres of the 1 °C-group contained less myofibrils than the two other groups. The phenotype
of the larvae at hatching was thus affected within these incubation temperatures. Although all groups were transferred to
the same temperature after hatching, the lowest egg incubation temperature (1 °C) still had a negative effect 5 d after hatching,
as these larvae were both smaller, less resistant to stress and had less functional muscles at the time of first feeding.
Our conclusion is therefore that 1 °C is close to, or below, the lower thermal tolerance limit for normal functional development
of Northeast Arctic cod. The results are discussed in relation to larval viability and recruitment of this species in the
wild.
Received: 4 February 1998 / Accepted: 10 July 1998 |
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