title: A multilevel approach to examining cephalopod growth using Octopus pallidus as a model.
abstract: Many aspects of octopus growth dynamics are poorly understood, particularly in relation to sub-adult or adult growth, muscle fibre dynamics and repro-somatic investment. The growth of 5 month old Octopus pallidus cultured in the laboratory was investigated under three temperature regimes over a 12 week period: seasonally increasing temperatures (14-18°C); seasonally decreasing temperatures (18-14°C); and a constant temperature mid-way between seasonal peaks (16°C). Differences in somatic growth at the whole-animal level, muscle tissue structure and rate of gonad development were investigated. Continuous exponential growth was observed, both at a group and at an individual level, and there was no detectable effect of temperature on whole-animal growth rate. Juvenile growth rate (from 1 to 156 days) was also monitored prior to the controlled experiment; exponential growth was observed, but at a significantly faster rate than in the older experimental animals, suggesting that O. pallidus exhibit a double-exponential two-phase growth pattern. There was considerable variability in size-at-age even between individuals growing under identical thermal regimes. Animals exposed to seasonally decreasing temperatures exhibited a higher rate of gonad development compared with animals exposed to increasing temperatures; however, this did not coincide with a detectable decline in somatic growth rate or mantle condition. The ongoing production of new mitochondria-poor and mitochondria-rich muscle fibres (hyperplasia) was observed, indicated by a decreased or stable mean muscle fibre diameter concurrent with an increase in whole-body size. Animals from both seasonal temperature regimes demonstrated higher rates of new mitochondria-rich fibre generation relative to those from the constant temperature regime, but this difference was not reflected in a difference in growth rate at the whole-body level. This is the first study to record ongoing hyperplasia in the muscle tissue of an octopus species, and provides further insight into the complex growth dynamics of octopus.
authors.affiliation: Fisheries, Aquaculture and Coasts Centre, Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 49, Tasmania 7001, Australia. jayson.semmens@utas.edu.au
authors.forename: Jayson
authors.initials: J
authors.lastname: Semmens
authors.forename: Zoë
authors.initials: Z
authors.lastname: Doubleday
authors.forename: Kate
authors.initials: K
authors.lastname: Hoyle
authors.forename: Gretta
authors.initials: G
authors.lastname: Pecl
mesh_terms: D000825:Animal Structures / Q000033:anatomy & histology; D000818:Animals; D005260:Female; D008297:Male; D023421:Models, Animal; D009132:Muscles / Q000033:anatomy & histology; D049831:Octopodiformes / Q000033:anatomy & histology / Q000254:growth & development*; D013696:Temperature