Divergence in buoyancy of the ecologically similar nototheniid fish Notothenia coriiceps and N. rossii

BARRERA ORO, ESTEBAN RODRIGO; EASTMAN, J.T.; MOREIRA, E.

Buenos Aires

Conferencia; XXXI SCAR 4th Open Science Conference; 2010

SCAR (Scientific Committee on Antarctic Research)

Although lacking a swim bladder, notothenioids inhabit pelagic and benthic habitatsand diversification in buoyancy is the ecological hallmark of their radiation. We studied thebuoyancy of sister species Notothenia coriiceps (NOC) and N. rossii (NOR) captured at KingGeorge/25 de Mayo Island. Measurements of buoyancy are expressed as percentagebuoyancy (%B = weight in water/weight in air x 100), with smaller numbers reflecting morebuoyant (i.e., less dense) species. Our samples encompassed a large number of individualsof wide size/age ranges: 95 NOC of 64–475 mm TL and 1–13 years; 99 NOR of 78–436 mmTL and 1–7 years. Both species are benthic as adults and have complex life cycles involvingpelagic stages and migrations. Mean %B of NOC (4.34%) was significantly greater (t =11.256, P <0.0001) than that of NOR (3.84%), reflecting the more active and migratorybehaviour of NOR over NOC. Fit lines for scatter plots of %B against length/weight werecurvilinear for both species with %B rising to a peak at 170 mm in NOC and 200 mm in NORand then falling to a level about 0.5 %B unit lower in the largest specimens (~450 mm and400 mm, respectively). Fulton’s condition factor (K), a measure of fish girth, begins trendingsteeply upward at 160–230 mm in NOC and at 170–240 mm in NOR. We conclude that theontogenetic decrease in %B reflects increasingly rapid growth of non-skeletal body tissuesand does not correspond to specific pelagic-demersal habitat shifts or migratory phases.