GROWTH CIRCLE PATTERNS IN THE OTOLITH OF THE GRAY FISH (Osteochilus melanopleurus) FROM THE SIAK AND KAMPAR RIVERS

Osteochilus melanopleurus can be found in the Siak and Kampar Rivers. The Kampar Rivers waters are better than that of the Siak River and it affects the growth of the fish. The growth pattern is reflected in the pattern of otolith growth rings. The research aims to understand the pattern of otolith growth rings of the O. melanopleurus from both rivers has been conducted from January to February 2021. There were 55 fishes captured (28 males and 27 females). The otolith was taken using tweezers and shaved manually using a soft grindstone. The dark growth ring pattern was investigated using a binocular microscope. Results showed the size of fish captured was 220 to 360 mm from Siak River and 310 to 370 mm from Kampar River. In the fish with the same standard length, the size of the otolith from the Siak River is heavier and longer than that of the Kampar River, which means that fish growth from the Kampar River is better than that of the Siak River. The length of an otolith from Siak River ranged from 1.875 – 3.275 mm, the width was ranged from 1.575–2.75 mm and the weight of otolith was 0.0039 – 0.0098 g, while the length of an otolith from Kampar River ranged from 2.375–3.275 mm, the width was ranged from 1.85–2.575 mm and the weight of otolith was 0.0042 –0.0076 g. The maximum number of the dark ring in the otolith from the Siak River was 4 and Kampar River was 2. The distance between the nucleus and the first dark ring of fish from both rivers was varied from 0.1–0.525 mm, and there was no special pattern. This fact indicates that the first dark ring was formed individually and they were not formed by a periodical incidents during the fish life

Partitioning maternal and exogenous diet contributions to otolith 87Sr/86Sr in Kokanee Salmon (Oncorhynchus nerka)

Strontium isotopes (87Sr/86Sr) recorded in the otoliths of Pacific Salmon (Oncorhynchus spp.) are commonly used to identify natal origin. For species that migrate at or soon after emergence, the embryonic region of the otolith provides the only record of provenance. However, maternal contribution of Sr from the yolk can confound the isotopic signature of the natal site. We experimentally quantified maternal and exogenous diet contributions to otolith 87Sr/86Sr over embryonic development in Kokanee salmon (O. nerka). Eggs from two populations in isotopically distinct lakes were incubated and reared in a common water source. Timing of developmental events and proportional contribution from yolk to otolith 87Sr/86Sr differed significantly between the two populations. We suggest that the magnitude of difference in 87Sr/86Sr between yolk and water, the relative concentrations of Sr and Ca in these isotopic sources, and population-specific effects on otolith growth and composition contribute to this variation. Understanding how these factors affect otolith 87Sr/86Sr could extend the use of otolith geochemistry for determining provenance to species and populations in which natal site rearing is limited.

Corrigendum to: Identifying physiological and environmental influences on otolith chemistry in a coastal fishery species

Otolith (ear stone) chemistry provides powerful insights into the lives of fish. Although frequently used to reconstruct past environments, the influence of physiology remains unsettled. As such, we investigated the relationships between otolith chemistry, physiological factors and environmental factors in an iconic fishery species, snapper (Chrysophrys auratus). Lifetime otolith profiles were analysed of carbon (δ13C) and oxygen (δ18O) isotopes, and elemental concentrations of lithium (Li:Ca), magnesium (Mg:Ca), manganese (Mn:Ca), strontium (Sr:Ca), and barium (Ba:Ca). Mixed-effects modelling alongside a detailed literature review was used to investigate physiological (age, otolith growth rate, fish size, sex) and environmental influences (sea-surface temperature and chlorophyll-a) on otolith chemistry. Carbon isotopes and magnesium related to physiological factors, suggesting their potential as physiological proxies. Physiology also weakly related to strontium and lithium. By contrast, oxygen isotopes, barium, and manganese (except for natal signatures) were suggested to provide insights into past environments. Our study stresses the importance of consistency in biological characteristics for study designs, and highlights the potential of physiological proxies for distinguishing between populations in uniform water bodies. This study has not only reinforced our confidence in field applications of otolith chemistry, but has furthered our understanding of the influence of physiology.

Otolith growth and zone formation during first maturity and spawning of Atlantic cod (Gadus morhua)

Specific impacts of somatic growth, sexual maturation, and spawning events on otolith zone formation in Atlantic cod (Gadus morhua) were assessed in a 33-month tank experiment, using Barents Sea cod and Norwegian coastal cod. High and low feeding ration combinations were used to mimic environmental stressors in the field. For both stocks, apparent macrostructural “spawning zones” in otoliths are registered in statutory stock monitoring programs to estimate age at maturity, thus adding key information to stock biomass assessments. We found that substantial energy investments in reproduction caused reductions in otolith growth and altered proportional width between translucent and opaque zones. These effects, however, were only statistically significant among individuals with high reproductive investments, while otoliths from individuals with low investments did not differ from the otoliths for immatures. Reproduction may thus not necessarily induce spawning zones, and alternatively, spawning zones may not necessarily reflect reproduction. Altogether, this suggests that the individual energy level, as a premise for metabolic activity, plays a key role in the formation of such zones and thus is related to environmental conditions.