Application of Effective Day Degrees in the Assessment of Stable Isotope Patterns in Developing Seahorses under Different Temperatures.

Sonia Valladares,Miquel Planas

doi:10.3390/ani10091571

Abstract

Simple SummaryTemperature affects fish development, with especially strong influence on juvenile growth rates and metabolism. The present study provides new insights on stable isotopes (δ13C and δ15N) for the understanding of growth and food assimilation in early developing European long-snouted seahorse Hippocampus guttulatus under different temperature levels. The effects of feeding status, ontogeny and temperature regimes on stable isotope patterns were assessed and modelled as function of development. We argue that chronological time is not a convenient developmental scale and we encourage the use of D°eff as temperature-independent developmental index in stable isotopes studies involving temperature comparisons.Relations between nutrient assimilation and growth rate in fishes may vary with abiotic factors such as temperature. The effects of feeding status, ontogeny and temperature regimes (15, 18 and 21 °C) on stable isotope (δ13C and δ15N) patterns were assessed in juveniles of the seahorse Hippocampus guttulatus. The use of effective day degrees (D°eff), day degrees (D°) and chronological time (age) were compared as development progress indices. Newborn seahorses were maintained at three temperature levels both deprived of food (5 days) or fed (30 days) on copepods or/and Artemia. Isotopic signatures in fed seahorses clearly differed from those in unfed juveniles. Temperature had a significant effect on δ13C values in fed juveniles throughout the experimental period. δ15N values also varied significantly with age, but not with temperature level. Faster growth and food assimilation in seahorses held at 18 and 21 °C were supported by faster variations in isotopic values. Our findings demonstrate that effective day degrees should be preferred over chronological time as index of developmental progress in temperature fluctuating scenarios or for comparative studios.

Highlights

The estimation of food intake, digestibility and assimilation patterns provides valuable information for the interpretation of growth and mortality rates of a consumer [1,2]
A direct method for overcoming these difficulties is the use of stable isotopes, whose values in consumer tissues reflect those of the food incorporated plus a trophic discrimination factor that occurs with nutrient assimilation [4]
The highest final survival occurred at 18 ◦ C (86 ± 0.4%), which was significantly higher than at 15 ◦ C (21 ± 2%) and 21 ◦ C (81 ± 0.2%) (Kruskal-Wallis test, p < 0.05)

Summary

Introduction

The estimation of food intake, digestibility and assimilation patterns provides valuable information for the interpretation of growth and mortality rates of a consumer [1,2]. Carbon and nitrogen stable isotopes (13 C and 15 N) have been successfully used as dietary tracers for assessing the food utilization by organisms [12,13,14,15]. Numerous factors such as environmental conditions (e.g., temperature), feeding rates, physiological and nutritional status of the consumer (e.g., stress, starvation) often cause modifications to food assimilation and differences in consumer isotope composition [16,17,18,19]. In the case of fish larvae, experimental stable isotope studies investigating the effects of environmental conditions on stable isotope incorporation are relevant in identifying environmental preferences of larvae, understanding larval nutrition needs, improving rearing techniques, and interpreting field stable isotope studies

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