Data from: Maximum cardiac performance of Antarctic fishes that lack haemoglobin and myoglobin: exploring the effect of warming on nature’s natural knockouts

Comparisons among related species provide valuable insight into the
functional consequences of natural genetic mutations. We assessed cardiac
function at ambient and elevated temperatures in Antarctic notothenioids
with contrasting levels of the oxygen binding proteins, haemoglobin (Hb)
and myoglobin (Mb), to elucidate changes in cardiac performance that may
compensate for impaired O2 transport. Notothenia coriiceps (Hb+Mb+) at 1oC
had the highest maximum cardiac work rate (WC) and pressure generating
capacity, but lowest relative ventricular mass and maximum cardiac output
(Q̇) when compared with two icefish species, Chionodraco rastrospinosus
(Hb-Mb+) and Chaenocephalus aceratus (Hb-Mb-). Cardiomegaly associated
with absence of Hb generated an exceptionally large maximum stroke volume
(VS) and Q̇, but a lower WC. However, C. rastrospinosus had a larger
ventricle, a higher intrinsic heart rate (fH), and greater maximum VS and
Q̇ than C. aceratus, suggesting that cardiac Mb has functional relevance.
Warming to 4oC increased fH, but only increased maximum Q̇ in icefishes,
while maximum WC and pressure development increased in N. coriiceps (both
~2.5x that of C. aceratus). The Hb+Mb+ myocardium generated considerable
Q̇ against raised afterload, unlike icefish hearts. The presence of Hb and
Mb enhances cardiac performance, and likely resilience to near-future
ocean warming.