FOR THE ENHANCED CARDIAC PERFORMANCE
OF WINTER FLOUNDER (Pleuronectes americanus)
Paula da Costa Mendonça
Ocean Sciences Centre, Memorial University of Newfoundland,
St. John’s, NL, Canada
Phone: +709 737 3112; Fax: +709 737 3220
Angela Gaylene Genge; Eric James Deitch; Anthony Kurt Gamperl
EXTENDED ABSTRACT ONLY - DO NOT CITE
Despite their abundance and diversity (Fletcher, 1975; Moyle and Cech, 1996), flatfish cardiovascular biology/physiology has not been extensively studied, and much of the published data on cardiac function may be inaccurate due to the use of indirect measurements and/or techniques (e.g. the Fick principle). Recently, Joaquim et al. (in press) performed the first direct in vivo measurements of
cardiac function in winter flounder and found that maximum stroke volume (S) V-1is extremely high in this species (1.5 ml g ventricle, 10ºC) compared with other
teleosts. To examine the factors that contribute to the high S in this species, in V
situ Starling curves and power curves, and in vitro pressure-volume curves were
determined for the winter flounder (Pleuronectes americanus), Atlantic cod
(Gadus morhua) and Atlantic salmon (Salmo salar).
Material and Methods
Wild winter flounder were captured in Conception Bay (Newfoundland), while hatchery-reared cod and salmon were obtained from a cage-site operation (Bay D’Espoir) and the Ocean Sciences Centre (OSC), respectively. All fishes were acclimated at 8 to 10 ? 1ºC for at least 4 weeks prior to experimentation.
In situ heart preparations at 8 to 10ºC were performed as previously described by Farrell et al. (1982) for sea-raven, but adapted for the flounder, cod and salmon.
To obtain pressure-volume curves (Forster and Farrell, 1994) the heart (without pericardium) was dissected free from the animal, and pressure-volume curves were generated for the atrium, ventricle and bulbus arteriosus of the 3 species. In addition, atrial:ventricular (A:V) and bulbus:ventricular (B:V) mass ratios were calculated to examine if the size of the heart chambers or their relative size
influences the shape of the pressure-volume curves.
After ln transforming the data for the Starling and pressure-volume curves, ANCOVA was used to test for homogeneity of slopes between species (p<0.05; rdSPSS Software). Maximum power values were obtained by fitting a 3 order
power curve (SigmaPlot Software) to the data of each fish. Differences in maximum power output (P), cardiac output (Q), heart rate (f), stroke volume HH
(S) and A:V and B:V mass ratios between species were assessed by ANOVAs V
and pairise Tukey tests (SPSS Software, p<0.05).
Results and Discussion
In situ maximum Q was not significantly between the three species, averaging -1-163 ml min kg. However, because of the small size of the flounder heart (RVM 0.05%), the maximum S achieved by the winter flounder was significantly V-1higher (2.2 ? 0.1 ml g ventricle) as compared with the Atlantic cod (1.7 ? 0.2) and Atlantic salmon (1.4 ? 0.1) (Fig.1A). The maximum P of the flounder heart H-1-1(7.6 ? 0.3 mW g) was significantly lower than the salmon (9.7 ? 0.5 mW g), -1but surprisingly similar to the cod (7.8 ? 0.6 mW g) (Fig.1B).
Cod and salmon hearts could generate in vivo resting levels of Q at negative
filling pressures (P), whereas the flounder heart required a positive Pof 0.4 inin cm HO to achieve resting Q. However, fewer increments in P were required 2in
by the flounder heart to achieve elevated levels of S. For instance, to achieve a V-1S of 1.4 ml g ventricle, the flounder heart only needed a P increase of 1.9 cm Vin
HO,whereas cod and salmon hearts required P increases of 2.9 and 6.9 cm 2 in-1HO, respectively. These data show that the high Svalues (in ml g ventricle) 2V
measured for the flounder are partly related to an enhanced sensitivity to filling pressure. This conclusion is supported by the pressure-volume curves, which
indicate that the flounder’s atrium, ventricle and bulbus are significantly more
compliant when compared to the cod and salmon (Fig.2).
A 2.5 1 6 2.0 ventricle)-1
Stroke Volume (ml g0.5
0.0-4-202468 Input Pressure (cm HO)212 B 10 )-18
4 Power Output (mW g
Output Pressure (cm HO)2
Figure 1. Starling curves (A) and Power Curves (B) for the winter
flounder (?), Atlantic cod (?) and Atlantic salmon (Δ) at 8 ºC. N=
7-8, except when numbers appear next t data point.
4O)2 3 2 Pressure (cm H 1 0
Pressure (cm H20 0 -200.00.51.01.52.02.5
Pressure (cm H20
0.00.51.01.52.02.53.03.5-1Volume (ml g chamber)
Figure 2. Pressure-volume curves for the atrium (A), ventricle (B) and
bulbus (C) of the winter flounder (?), Atlantic cod (?) and Atlantic
salmon (Δ) at 8-10 ºC. N? 6, except salmon ventricle where N= 2.
Although, the flounder’s A:V ratio (0.22) was comparable to the cod (0.21) and
the salmon (0.18), the flounder’s B:V ratio (0.59) was significantly higher (cod 0.37; salmon 0.22). In fact, the high B:V mass ratio may be partially responsible with the low arterial pressures reported for the flounder.
In conclusion, the S measured in winter flounder (per gof ventricle) is V
extremely high. This high S is related to 1) a pronounced Starling curve; 2) V
more compliant heart chambers; and 3) a high B:V mass ratio. Our data support the in vivo data of Joaquim et al. (in press) and others, which show that the
cardiovascular system of flatfish is a high volume, low pressure design. Further, these data suggest that the pericardium, and thus vis a fronte filling, may not be
important for cardiac function in flatfishes.
Farrell A, MacLeod K, Driedzic W. 1982. The effects of preload, after load, and
epinephrine on cardiac performance in the sea raven, Hemitripterus
americanus. Can. J. Zool. 60(3165-71).
Fletcher G. 1975. The effects of capture, "stress," and storage of whole blood on
the red blood cells, plasma proteins, glucose, and electrolytes of the winter
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Forster M, Farrell A. 1994. The volumes of chambers of the trout heart. Comp.
Biochem. Physiol. 109 A(1):127-32.
Joaquim, N., Wagner, G.N. and Gamperl, A.K.. In Press. Cardiac function and
critical swimming speed of the winter flounder (Pseudopleuronectes
americanus) at two temperatures. Comp. Biochem. Physiol.
rdMoyle PB, Cech J. 1996. Fishes: an introduction to ichthyology (3 edition).
Prentice-Hall, Inc. p 339-45.
PCM was supported by a Foundation for Science and Technology doctoral fellowship (Portugal), EJD was supported by Natural Sciences and Engineering Research Council of Canada (NSERC) IPS scholarship, and AKG and AGG were supported by an NSERC discovery grant. We are also grateful to Dr. Trevor Avery for statistical advice, and AquaBounty (Canada) for supplying the Atlantic salmon used in this research.