In Denmark cod with all three genotypes can be caught, andexperiments with a shuttle box showed that the preferredtemperature of HbI-1 and HbI-2 was 15.4 and 8.2 °C, respectively.When exposed to hypoxia the preferred temperature of HbI-1 codchanged from 15.4 to 9.8 °C, while the HbI-2 cod showed no effect.

McFarland compared oxygen consumption of cod caught inDenmark with haemoglobin type HbI-1 and HbI-2, but found nosignificant difference, so it is still unknown why Greenland Atlanticcod have a higher metabolic rate.

doi:10.1016/j.cbpa.2008.04.579

SETE.17Why hypoxic bradycardia in fishes?

A. Farrell (University of British Columbia)

Why do certain fish respond to environmental hypoxia withbradycardia whereas mammals respond with tachycardia? Equivo-cal results regarding a potential benefit to gill oxygen transferopen the door for the present analysis of potential benefits ofhypoxic bradycardia to cardiac function. The potential benefits,which include improving contractility through a negative forcefrequency effect, reducing cardiac oxygen demand by improvingmechanical efficiency, and improving cardiac oxygen delivery totrabecular and compact cardiac muscle, recognize the ability of thefish heart to considerably vary stroke volume and its reliance onoxygen contained invenous blood. Further insights to the benefitsof hypoxic bradycardia are provided by the observations thatanemic trout, Antarctic fish, anoxia-tolerant fishes and air breath-ing fishes do not display hypoxic bradycardia. Research supportprovided by NSERC Canada.

doi:10.1016/j.cbpa.2008.04.580

SETE.18Temperature tolerance and respiration in coral reef fishes

G. Nilsson (University of Oslo)

Abstract not available.

doi:10.1016/j.cbpa.2008.04.581

SETE.19Intra-specific variation in muscle fibre phenotype

I.A. Johnston, I.P.G. Amaral, V.L.A. Vieira (University of St Andrews)

The large increase in body size observed between larval andadult fish requires the continuous production of fast myotomalmuscle fibres until around 40% of the maximum length.Subsequent growth in myotomal girth only involves fibrehypertrophy, although myotubes can still be produced to repairdamage following injury. The optimal fibre number hypothesisprovides a physiological explanation for changes in final fibre

number (FFN) with body size and environment. The hypothesisenvisages an optimal fibre number which minimises the energycosts of maintaining ionic homeostasis in the muscle (Johnstonet al., 2003, 2006). This presentation will consider various testsof the optimal fibre number hypothesis in marine andanadromous fishes and examine the relative importance ofselection and developmental plasticity in generating theobserved variation in FFN between populations. Recent genomicapproaches to investigate the control of fibre number andexperiments to determine the consequences of intraspecificvariation in FFN for whole animal performance will bediscussed.

Johnston, I.A., Fernandez, D., Calvo, J., Vieira, V.L.A., North, T.W.,Abercromby, M., and Garland, T. Jr. (2003). Reduction in muscle fibrenumber during the adaptive radiation of Notothenioid fishes: aphylogenetic perspective. J. Exp. Biol. 206, 25952609.

Johnston, I.A., Abercromby, M., and Andersen, Ø. (2006). Musclefibre number varies with haemoglobin phenotype in Atlantic cod aspredicted by the optimal fibre number hypothesis. Biol. Lett. 2,590592.

doi:10.1016/j.cbpa.2008.04.582

SETE.20Haemoglobin polymorphism and red blood cell sickling in marinefishes

M. Berenbrink (University of Liverpool); D. McDonald (University ofMiami); P. Koldkjaer (University of Liverpool)

In human sickle cell disease a single surface amino acidmutation in the beta globin chain leads to the formation of largeinsoluble haemoglobin (Hb) aggregates at low oxygen tension.This may cause peculiar cell deformations or ‘sickling’, which cancause vascular occlusion, organ failure and death. In a classicexample of balanced polymorphism, the frequency of the mutatedbeta-globin allele is kept elevated in certain human populationsbecause of the benefits for heterozygote carriers against infectionwith malaria parasites. In vitro, red blood cell sickling is alsofound in several marine fish species such as the oyster toadfish,Atlantic cod and other codfishes (Harison et al., 1998). Recently,we have demonstrated its occurrence in vivo in whiting, Merlan-gus merlangius, and suggested that it may be involved inprotection against parasite infection (Koldkjaer and Berenbrink,2007). However, the molecular and genetic bases of sickling inmarine fishes are poorly understood. Here we describe largeintraspecific differences in red blood cell sickling in the Gulftoadfish Opsanus beta, which are associated with a complex Hbpolymorphism. In contrast, we show that in Atlantic cod nearly100% sickling can be induced in all Hb genotypes that comprisethe well-known HbI polymorphism. These results indicate distinctintra and interspecific differences in red blood cell sickling inmarine fishes, although its relative costs and benefits remain tobe established.

References

Harosi, et al., 1998. Biol. Bull. 195, 5–11.Koldkjaer, Berenbrink, 2007. J. Exp. Biol. 210, 3451–3460.

doi:10.1016/j.cbpa.2008.04.583

S207Abstracts / Comparative Biochemistry and Physiology, Part A 150 (2008) S203–S210