Applied Ecophysiology: An Integrative Form to Know How Culture Environment Modulates the Performance of Aquatic Species from an Energetic Point of View - Aquaculture and the Environment: A Shared Destiny - page 182

LDH activity and Lactate concentration as well as oxygen consumption coincide with a
significant reduction in hemolymphatic hemocytes and finally a survival reduction to 70%.
In accordance with these results and applying Ecophysiology to the development of
cultivation techniques, the rearing systems were modified to ensure the adequate Oxygen
supply in the first millimeter over the bottom surface, the place where juveniles of the
southern king crab Lithodes santolla feed, moult and growth.
5. Modelling individual growth: Size-at-age variability in cephalopods and
mixed models tools
Both individual and population growth is central to aquaculture practice and research, and
modelling growth has been an important aim in methodological and theoretical studies
Moltschaniwskyj, (2004); Vigliola & Meekan, (2009). Models have been extensively
developed and applied to understand population growth (e.g. Malthussian models, logistic
models, Leslie matrix, etc.), and those for individual growth have followed closely (von
Bertalanffy model). Methods for measuring and modelling individual growth can be
classified as either indirect or direct Semmens et al . ,(2004). Indirect methods are those using
modal progression analysis based on length-frequency data obtained from animals caught
in the wild. These have been used to predict length-at-age in individuals of a variety of both
vertebrate and invertebrate fisheries Solis-Ramírez, (1997); Cortez et al . , (1999) Direct
methods, such as mark and recapture using a variety of tags, have been used to follow the
growth of juvenile and adult stages in the wild Sousa Reis & Fernándes, (2002); Cortez et al . ,
(1999).
From an ecophysiological point of view, however, more useful are direct methods
examining the growth of individuals whose age and specific culture conditions are known.
The growth of an individual is the result of a series of energy transformations that begin
with food ingested, together with the balance between the uses and destinations of the
energy contained in that food Lucas, (1993); Rosas et al . , (2007). Thus, the growth curve
represents the manner in which the physiological and energy demands are expressed over
time O'Dor & Wellls, (1987); Pauly, (1998) at differing levels of biological organization, i.e.
body size, organs, tissue, and cells Moltschaniwskyj, (2004). In the context of energy balance,
the ultimate need to measure and compare the way in which individuals grow becomes
clear: individual growth models can be used not only to predict size at age, hence biomass
productions at certain points in time, but can also serve to estimate growth curve
parameters that can later be compared amongst different culture conditions.
The mathematical tool generally used to obtain growth curve parameters is least square
fitting, which can be used both for linear and non-linear models. The linear least-squares
problem occurs in statistical regression analysis where it has a closed-form solution. The
non-linear problem has no closed-form solution and is usually solved by iterative
refinement, where chi-square ( X 2 ) and probability (p) values are obtained and evaluated at
each iteration.
Analyses of individual growth have commonly involved fitting linear regression models of
weight against time. However, such an approach involves difficulties because the weight vs.
time relationship is rarely linear and, when it is, it is only for very short and specific periods.
Moreover, repeated measurement of the same individuals violates an indispensible