Understanding octopus growth: patterns, variability and physiology

Abstract

Octopuses are generally characterised by rapid non-asymptotic growth, with high individual variability. However, in situ octopus growth is not well understood. The lack of an ageing method has resulted in the majority of our understanding of octopus growth coming from laboratory studies. Despite not being applicable to cephalopods, Modal Progression Analysis (MPA) of length–frequency data is the most common method for examining in situ octopus growth. Recently, counting growth increments in beaks and vestigial shells, and quantifying lipofuscin in brain tissue, have all shown promise for the ageing octopus. Octopuses generally demonstrate two-phase growth in the laboratory, with physiological changes possibly associated with the switch between an initial rapid exponential phase and a slower power growth phase. Temperature and food ration and quality are key factors influencing the initial growth phase. Temperature, however, does not appear to affect the second phase in any consistent way, perhaps because maturity stage can influence the growth response. There may be basic differences in the mechanisms of octopus muscle growth compared with that of other cephalopods. Furthermore, higher relative maintenance energy expenditure, along with the low energy content of their prey, may account for the relatively slow growth of deep-sea octopuses compared to littoral species.

Determining the age and growth of wild octopus using stylet increment analysis

“…All 4 of these methods have intrinsic limitations: (1) beak microstructure increment analysis is affected by processes such as feeding that wear down the beak, resulting in inaccurate estimates (Hernández-López & Castro-Hernández 2001); (2) laboratory derived findings are not guaranteed to be transferable to wild populations (Joll 1977, Pecl & Moltschaniwskyj 1999; (3) factors such as tagging mortality, growth reduction due to stress, inability to predict age before the tag date, reliance on consistent recaptures and accurate reporting must all be considered when conducting a tag-recapture study ; and (4) histological quantification of lipofuscin is yet to be validated in animals of known age (Semmens et al 2004). What is required is an accurate and validated method of age determination that uses similar internal structures to those found in teleost fish (otoliths and vertebrae), which does not rely on external features such as beaks and morphometric measurements, avoids the uncertainty of laboratory studies and is not as limited in scope as tagging studies.…”

“…The extent to which octopus stocks can withstand this escalating pressure is largely unknown. Of paramount importance is the need for an accurate, reliable, cost effective and easy to use method of octopus age estimation (Semmens et al 2004). Without accurate age estimation, studies on octopus growth, recruitment, productivity and population structure rely on assumptions derived from morphological assessments and catch data (Jackson et al 1997, Campana 2001.…”

“…A commonly applied method that uses mantle length as the defining measure of octopus growth is modal progression analysis (MPA). MPA relies on the assumption that age is closely related to size (Challier et al 2002); however, cephalopod growth in general is extremely variable (Forsythe & Van Heukelem 1987, Semmens et al 2004, rendering this assumption incongruous (Mangold & von Boletzky 1973, Jackson et al 2000. Lack of a strong age/size relationship combined with the generally short life span (< 2 yr) of most octopus species (Boyle & Rodhouse 2005), prevents the practical application of cohort analysis without intensive sampling (Cortez et al 1999).…”

Protein Synthesis, Degradation, and Retention: Mechanisms of Indeterminate Growth in Cephalopods

“…In contrast to other molluscs, Euprymna had values that were well below the nearly 100% protein synthesis retention efficiency value recorded for Octopus (Houlihan et al 1990). It is worth noting that Octopus and Euprymna have dramatically different life-history characteristics: Octopus are terminal spawners (Semmens et al 2004), while Euprymna are multiple spawners (Steer et al 2004). The faster specific growth rate (SGR) observed in the younger/smaller individuals compared with in the older/larger individuals was a function of greater protein synthesis retention efficiency, faster fractional rates of protein synthesis, and, to a lesser extent, the concentration of RNA in the tissues.…”

Reproductive traits of sandbird octopus, Amphioctopus aegina (Gray, 1849) from Mandapam coastal waters (Palk Bay), Southeast Coast of India

“…Most species of octopus species have simultaneous terminal spawning events that can occur year round or in one or two seasonal peaks. Males have year round maturation and a short life span of less than <2 years (Guerra 1975;Hatanaka 1979;Goncalves 1991;Sanchez and Obarti 1993;Semmens et al 2004).…”