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First published online March 16, 2007
Journal of Experimental Biology 210, 1170-1182 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.002188
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Persistent effects of incubation temperature on muscle development in larval haddock (Melanogrammus aeglefinus L.)

D. John Martell1,2,* and James D. Kieffer2

1 Fisheries and Oceans Canada, St Andrews Biological Station, 531 Brandy Cove Road, St Andrews, NB, E5B 2L9, Canada
2 Department of Biology and Canadian Rivers Institute, University of New Brunswick, PO Box 5050, Saint John, NB, E2L 4L5, Canada


Figure 1
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  		Fig. 1. Cross-section of the outer epaxial musculature of a 2 d.p.h. larval haddock incubated at 6°C, stained with Paragon, demonstrating distinctive cellular and structural features. Bar, 20 µm. spF, superficial myofibres; dF, deep myofibres; ssPZ, superficial-deep septum proliferation zone; mt, mitochondria; white arrowheads, small new myofibres. For descriptive purposes, the inset (50% size of the main figure) illustrates the outlines of individual myofibres.

 

Figure 2
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  		Fig. 2. Cross-section of the dorsal epaxial musculature at the level of the posterior gut from a 21 d.p.h. larval haddock incubated at 6°C, stained with Paragon, indicating distinctive cellular features. Bar, 30 µm. spF, superficial myofibres; dF, deep myofibres; sF, small myofibres; mt, mitochondria; ssPZ, superficial-deep septum proliferation zone; daPZ, dorsal apical proliferation zone; nt, neural tube.

 

Figure 3
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  		Fig. 3. Cross-section of the dorsal epaxial musculature at the level of the posterior gut of a 28 d.p.h. larval haddock incubated at 6°C, stained with Paragon, illustrating distinctive myotomal features about the horizontal myotome. Bar, 30 µm. spF, superficial myofibres; dF, deep myofibres; sPZ, superficial proliferation zone; ssPZ, superficial-deep septum proliferation zone; hmy, horizontal myoseptum; Lln, lateral line nerve.

 

Figure 4
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  		Fig. 4. Effect of incubation temperature on the post-hatch (A) geometric mean equivalent diameter and (B) mean number of superficial myofibres (note log y-axis) in one quadrant of the dorsal epaxial myotome in haddock reared in a constant 6°C post-hatch environment. Values are means ± 1 s.e.m. (N=71). Incubation temperature treatments: 4°C, circles; 6°C, squares; 8°C, triangles.

 

Figure 5
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  		Fig. 5. Frequency distributions of superficial equivalent diameters of all myofibres present in one quadrant of the haddock dorsal epaxial myotome binned into 2.5 µm diameter classes from 2 until 28 d.p.h. among the three incubation temperature treatments (A, 4°C; B, 6°C; C, 8°C). Values are means ± 1 s.e.m. (N=71) *Bars marked by a horizontal line are significantly different between consecutive days (P<0.05). Arrows (->) indicate temporal trends and are described in text.

 

Figure 6
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  		Fig. 6. Effect of incubation temperature on the post-hatch (A) geometric mean diameter and (B) mean number of deep myofibres (note log y-axis) in one quadrant of the dorsal epaxial myotome in haddock reared in a constant 6°C post-hatch environment. Values are means ± 1 s.e.m. (N=71) Incubation temperature treatments: 4°C, circles; 6°C squares; 8°C, triangles.

 

Figure 7
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  		Fig. 7. Frequency distributions of superficial equivalent diameters of all myofibres present in one quadrant of the haddock dorsal epaxial myotome binned into 2.5 µm diameter classes from 2 until 28 d.p.h. among the three incubation temperature treatments (A, 4°C; B, 6°C; C, 8°C). Values are means ± 1 s.e.m. (N=71). *Bars marked by a horizontal line are significantly different between consecutive days (P<0.05). The diagonal grey arrow indicates the temporal shift in the occurrence of the hyperplastic event and is described in text.

 

Figure 8
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  		Fig. 8. Logarithmic regressions describing the relationship between total number of deep myofibres and their mean equivalent diameter in one quadrant of the post-hatch larval dorsal epaxial myotome among the three incubation treatments (4°C, 6°C, 8°C). Circles, 4°C (lny=2.60–0.001x, r2adj=0.17); squares, 6°C (lny=2.63–0.001x, r2adj=0.62); triangles, 8°C (lny= 3.00–0.003x, r2adj=0.79). Logarithmic regressions were fitted to raw data by least-squares methods. All regressions were significant (P<0.05).

 




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