survival success during the early life stages. Several factors affect fish larval
mortality rates during the ELHS, although the most important ones are mortality
caused by enhanced predation and/or starvation (Hewitt et al. 1985; McGurk 1986;
Bailey and Houde 1989).
The survival of ELHS is therefore crucial for stock recruitment where small
changes in growth rates can have important repercussions on larval mortality
(Houde 1987, 2008). Mortality rates during early life are influenced by starvation
and predation, generally in that sequence because starvation leads to poorer nutritional status of larvae making them more vulnerable to predation (Bailey and Houde
1989; Folkvord and Hunter 1986). Also, slower growth rates turn fish larvae extend
temporally the ontogenic development at particular sensitive stages, thereby increasing predation pressure (Buckley 1984; Folkvord and Hunter 1986).
Therefore, somatic larval growth rates are critical in determining the time that
larvae spend in the size classes more susceptible to be preyed upon. The research
conducted on growth and condition studies at ELHS of small pelagics has shown that
growth rates are influenced mainly by the surrounding temperature regime and the
amount and quality of trophic resources (Ramírez et al. 2001; García et al. 2003;
Mercado et al. 2007), although maternal effects can have a consequential influence
on growth variability (García et al. 2003; Uriarte et al. 2016).
Temperature is a key factor controlling fish growth. Temperature affects metabolic rates of ELHS by increasing or decreasing the catabolism and anabolism of
proteins and therefore the accretion of muscular tissue and the development organs
during the development of ELHS. Several studies have reported enhanced larval
growth at higher temperatures both in the field- and in laboratory-reared larvae
(Blaxter 1991; Folkvord et al. 2004). On the other hand, nutritional condition indices
are also affected by temperature. Thus, the existing studies on this subject (e.g.,
Goolish et al. 1984; Ferguson and Danzmann 1990) have shown that larval fish
RNA/DNA tends to decrease with increasing seawater temperature. According to
Goolish et al. (1984), the underlying reason for a decline in RNA/DNA in fish
inhabiting increased seawater temperature would be due to the existence of a
metabolic mechanism that compensates for lower RNA activity at lower temperatures, producing an increase in RNA concentration.
Alternatively, food availability (i.e., suitable prey density) and larval success in
capturing their prey affect directly to the intake rates of proteins, carbohydrates,
lipids, and other nutrients by fish larvae. Laboratory and mesocosm experiments
have shown that food availability directly affects somatic larval growth, with wellfed larvae growing at faster rates than larvae under poor food availability. Food
availability not only affects growth, but it also affects the biochemical composition
of larval tissue. A poor nutritional condition, or even starvation caused by competition for food resources or by low prey density, not only has a direct effect on
protein synthesis and tissue accretion rates, but it also turns larvae more sensitive to
predators as their swimming capacity is reduced, thus prone to predators (Purcell
1985; Purcell and Grover 1990).
The findings reported by earlier research studies on larval growth (based on
otolith microstructure) and nutritional condition (mainly based on RNA/DNA)
504
A. García et al.
mortality rates during the ELHS, although the most important ones are mortality
caused by enhanced predation and/or starvation (Hewitt et al. 1985; McGurk 1986;
Bailey and Houde 1989).
The survival of ELHS is therefore crucial for stock recruitment where small
changes in growth rates can have important repercussions on larval mortality
(Houde 1987, 2008). Mortality rates during early life are influenced by starvation
and predation, generally in that sequence because starvation leads to poorer nutritional status of larvae making them more vulnerable to predation (Bailey and Houde
1989; Folkvord and Hunter 1986). Also, slower growth rates turn fish larvae extend
temporally the ontogenic development at particular sensitive stages, thereby increasing predation pressure (Buckley 1984; Folkvord and Hunter 1986).
Therefore, somatic larval growth rates are critical in determining the time that
larvae spend in the size classes more susceptible to be preyed upon. The research
conducted on growth and condition studies at ELHS of small pelagics has shown that
growth rates are influenced mainly by the surrounding temperature regime and the
amount and quality of trophic resources (Ramírez et al. 2001; García et al. 2003;
Mercado et al. 2007), although maternal effects can have a consequential influence
on growth variability (García et al. 2003; Uriarte et al. 2016).
Temperature is a key factor controlling fish growth. Temperature affects metabolic rates of ELHS by increasing or decreasing the catabolism and anabolism of
proteins and therefore the accretion of muscular tissue and the development organs
during the development of ELHS. Several studies have reported enhanced larval
growth at higher temperatures both in the field- and in laboratory-reared larvae
(Blaxter 1991; Folkvord et al. 2004). On the other hand, nutritional condition indices
are also affected by temperature. Thus, the existing studies on this subject (e.g.,
Goolish et al. 1984; Ferguson and Danzmann 1990) have shown that larval fish
RNA/DNA tends to decrease with increasing seawater temperature. According to
Goolish et al. (1984), the underlying reason for a decline in RNA/DNA in fish
inhabiting increased seawater temperature would be due to the existence of a
metabolic mechanism that compensates for lower RNA activity at lower temperatures, producing an increase in RNA concentration.
Alternatively, food availability (i.e., suitable prey density) and larval success in
capturing their prey affect directly to the intake rates of proteins, carbohydrates,
lipids, and other nutrients by fish larvae. Laboratory and mesocosm experiments
have shown that food availability directly affects somatic larval growth, with wellfed larvae growing at faster rates than larvae under poor food availability. Food
availability not only affects growth, but it also affects the biochemical composition
of larval tissue. A poor nutritional condition, or even starvation caused by competition for food resources or by low prey density, not only has a direct effect on
protein synthesis and tissue accretion rates, but it also turns larvae more sensitive to
predators as their swimming capacity is reduced, thus prone to predators (Purcell
1985; Purcell and Grover 1990).
The findings reported by earlier research studies on larval growth (based on
otolith microstructure) and nutritional condition (mainly based on RNA/DNA)
504
A. García et al.