Larval Otoliths Research Articles

Flow and thermal regimes altered by a dam caused failure of fish recruitment in the upper Mekong River

Abstract Riverine fishes have been increasingly threatened by the global proliferation of both small dams and large hydropower projects to meet the soaring water, energy and food demands from growing human populations and urbanisation. However, empirical evidence of the direct effects on a specific species before and after dam construction and operation is rare. Causes of population decline vary among species and, although little known, they are of great importance for successful environmental flow regulation. We monitored the hydroenvironment and population dynamics of a Schizothoracinae fish (Schizothorax lissolabiatus) for 9 years before and after dam (i.e., Dahuaqiao) construction in the upper Mekong River to understand fish response processes and the underlying mechanisms. Optimal hydroenvironmental conditions for key reproduction stages (e.g., pre‐spawning, hatching and post‐hatching) were reconstructed using daily increment analysis of larval otoliths and hydroenvironmental data. The flow regime was substantially disrupted by the dam, and water temperature was only slightly changed. The disappearance of young of the year from downstream after dam operation indicates that the changed hydroenvironment caused recruitment failure in S. lissolabiatus. By matching optimal hydroenvironmental conditions for S. lissolabiatus reproduction with the monitored hydroenvironmental data series before and after dam operation, we found that changes in thermal regime alone caused narrowing of the reproduction window by an average of 41%, whereas flow‐regime change alone narrowed it by 96% and it was narrowed by 98% for thermal and flow changes combined. This study shows that the altered flow regime, but not the thermal regime, was the primary driver of the recruitment failure of S. lissolabiatus. The findings highlight the importance of prioritising flow‐regime management to improve recruitment success for S. lissolabiatus and to favour the persistence of other imperilled Schizothoracinae fishes and native species in dammed rivers.

Effect of egg size on the growth rate and survival of wild walleye pollock Gadus chalcogrammus larvae

AbstractTo clarify the survival process of walleye pollock larvae of the Japan Pacific stock in relation to the individual egg size, we estimated the original relative egg diameter from the diameter of the hatch check formed on larval sagittal otoliths. Significant positive correlations were obtained between egg diameter and embryonic body length, yolk sac volume, and lapillar otolith diameter in 3‐year groups (2013–2015 year classes) collected with a plankton net in Funka Bay. Embryos before hatching were without a check; however, checks were observed on all larval otoliths just after hatching. The check diameters showed significant positive regressions to age at collection (days after hatching) in 2014 and 2015 year classes, however not in the 2013 year class. Diameters of eggs collected with a ring net in Funka Bay gradually increased from 2013 to 2015 year classes. During the 2013–2015 spawning seasons, the proportion of adult females of the 2007 and 2009 year classes, which had relatively high abundances, gradually increased to higher proportions with age (43%, 57%, and <73%, respectively), indicating that the mechanism by which the eggs gradually became larger. The low water temperature experienced by the spawners ca. 2 months earlier, advancement in spawner age, and increase of repeat spawners (at least twice in their life time) would contribute to the increase in egg size and growth and survival rate of walleye pollock larvae.

Effect of Temperature on the Daily Increment Deposition in the Otoliths of European Sardine Sardina pilchardus (Walbaum, 1792) Larvae

Otolith microstructure analysis is a valuable tool to evaluate the relationship between larval age and growth and how it relates to environmental variability. Otolith growth and daily increment deposition were analyzed in sardine (Sardina pilchardus) larvae reared in the laboratory under different temperatures (13, 15, and 17 °C), with a diet rich in microalgae, rotifers, and copepods Acartia grani. The number and width of growth increments, first-check and otolith diameter were determined in the otoliths and then related to larval age and total length. At hatching, the sagittal otoliths consisted of a lenticular core with a diameter of 10.56 μm (±1.07 μm SD). Somatic growth increased with the increasing temperature and the growth rate of larvae reared at 13 and 15 °C was significantly lower than for larvae reared at 17 °C. At 17 °C, otoliths exhibited a higher diameter with wider increments than at 13 °C. There was a high variability of increment counts-at-age for larvae reared within the same temperature treatment. The increase of growth increments with larval size was higher for larvae reared at 17 °C until 35 days post-hatching than those growing at 15 °C. Scanning electronic microscopy confirmed that increments are deposited daily, with an average width smaller than 1 µm and as low as 0.33 μm, therefore impossible to distinguish using light microscopy. At colder temperatures, larval otoliths had thinner and less marked increments and lower growth rates, which can lead to incorrect age determinations. The effect of temperature on the otolith microstructure can help in identifying strong temperature gradients experienced by wild sardine larvae.

Extensive larval dispersal and restricted movement of juveniles on the nursery grounds of sole in the Southern North Sea

Connectivity between spawning and nursery grounds influences the colonization, replenishment and resilience of populations of marine organisms. Connectivity rate, measured as the exchange of individuals between spawning and nursery grounds, is therefore a crucial determinant of stock size. However, connectivity of early-life stages is hard to explore due to sampling limitations and insufficient knowledge on potential larval sources. Here we present new insights into pre- and post-settlement dispersal of the common sole (Solea solea L.) at a spatial scale of 5–500 km in the Southern North Sea. Patterns at a scale of <100 km were considered local, whereas patterns further than 100 km were considered regional. Multi-elemental signatures of the otolith edge of 213 juvenile sole were used to discriminate at 79% of overall accuracy three main nursery grounds in the Southern North Sea, namely UK coast, Belgian coast and Dutch Wadden Sea. Interregional differences in otolith composition (especially for Mg, Mn and Ba) suggest that sole migration following settlement is limited in the Southern North Sea. Elemental signatures of the same fish indicated mixing during larval dispersal. Each nursery ground recruited an important mix of juveniles from three of the four chemically distinct natal sources identified from the larval otolith signatures. However the percentage of correct regional re-assignment varied from 67 to 80% with a maximum in the Wadden Sea. The results contributed to the validation of biophysical models of larval drift. Our findings support decision making for both fisheries management and marine spatial planning at the national and European level.

Ontogeny of Otolith Formation in Two Demersal Estuarine Reef Fishes

Abstract Planktonic reef fish larvae locate and orient to reefs during settlement. Consequently, metamorphosis occurs in appropriate juvenile and/or adult habitats. Larval fish use otoliths for hearing (sagittae and asterisci) as well as equilibrium (lapilli) required for directional swimming. Striped blenny (Chasmodes bosquianus) and naked goby (Gobiosoma bosc) larvae, settled individuals, and juveniles were used to describe otolith ontogeny from hatching through settlement, the transition from pelagic to benthic habitats, and metamorphosis. Larvae hatched from nests collected in North Inlet estuary, SC, were cultured from May through July in 2012 and 2013 at ambient temperatures. Sagittae and lapilli were present at hatching in both species. Asterisci were only observed in settlement (gobies and blennies) or metamorphosis (blennies) stage fishes, regardless of age (days post-hatch). Otoliths within a pair were symmetrical. Fish total length increased faster than sagittae otolith length in settlement stage blennies and postflexion gobies. The allometric model explained ∼90% of the variability in sagittae otolith length with total length for both species. Settlement occurred 15–20 days post-hatch in striped blennies and 19–27 days post-hatch in naked gobies. Asterisci were found in 100% of settlement stage striped blennies and 67% of naked gobies. We hypothesize that the presence of asterisci in settlement stage demersal oyster reef fishes facilitates identification of and orientation to suitable settlement habitats thereby enhancing recruitment success.

Regulatory mechanisms of miR-96 and miR-184 abnormal expressions on otic vesicle development of zebrafish following exposure to β-diketone antibiotics

Chronic ototoxicity of β-diketone antibiotics (DKAs) to zebrafish (Danio rerio) was explored in detail by following abnormal expressions of two hearing-related miRNAs. Dose-dependent down-regulation of miR-96 and miR-184 was observed in otoliths during embryonic-larval development. Continuous DKA exposure to 120-hpf larva decreased sensitivity to acoustic stimulation. Development of otolith was delayed in treatment groups, showing unclear boundaries and vacuolization at 72-hpf, and utricular enlargement as well as decreased saccular volume in 96-hpf or latter larval otoliths. If one miRNA was knocked-down and another over-expressed, only a slight influence on morphological development of the otic vesicle occurred, but knocked-down or over-expressed miRNA both significantly affected zebrafish normal development. Injection of miR-96, miR-184 or both micRNA mimics to yolk sac resulted in marked improvement of otic vesicle phenotype. However, hair cell staining showed that only the injected miR-96 mimic restored hair cell numbers after DKA exposure, demonstrating that miR-96 played an important role in otic vesicle development and formation of hearing, while miR-184 was only involved in otic vesicle construction during embryonic development. These observations advance our understanding of hearing loss owing to acute antibiotic exposure and provide theoretical guidance for early intervention and gene therapy for drug-induced diseases.

Strong evidence for changing fish reproductive phenology under climate warming on the Tibetan Plateau.

Phenological responses to climate change have been widely observed and have profound and lasting effects on ecosystems and biodiversity. However, compared to terrestrial ecosystems, the long-term effects of climate change on species' phenology are poorly understood in aquatic ecosystems. Understanding the long-term changes in fish reproductive phenology is essential for predicting population dynamics and for informing management strategies, but is currently hampered by the requirement for intensive field observations and larval identification. In this study, a very low-frequency sampling of juveniles and adults combined with otolith measurements (long axis length of the first annulus; LAFA) of an endemic Tibetan Plateau fish (Gymnocypris selincuoensis) was used to examine changes in reproductive phenology associated with climate changes from the 1970s to 2000s. Assigning individual fish to their appropriate calendar year class was assisted by dendrochronological methods (crossdating). The results demonstrated that LAFA was significantly and positively associated with temperature and growing season length. To separate the effects of temperature and the growing season length on LAFA growth, measurements of larval otoliths from different sites were conducted and revealed that daily increment additions were the main contributor (46.3%), while temperature contributed less (12.0%). Using constructed water-air temperature relationships and historical air temperature records, we found that the reproductive phenology of G.selincuoensis was strongly advanced in the spring during the 1970s and 1990s, while the increased growing season length in the 2000s was mainly due to a delayed onset of winter. The reproductive phenology of G.selincuoensis advanced 2.9days per decade on average from the 1970s to 2000s, and may have effects on recruitment success and population dynamics of this species and other biota in the ecosystem via the food web. The methods used in this study are applicable for studying reproductive phenological changes across a wide range of species and ecosystems.

Effects of the Blob on settlement of spotted sand bass, Paralabrax maculatofasciatus, to Mission Bay, San Diego, CA.

The West Coast of the United States experienced variable and sometimes highly unusual oceanographic conditions between 2012 and 2015. In particular, a warm mass of surface water known as the Pacific Warm Anomaly (popularly as “The Blob”) impinged on southern California in 2014, and warm-water conditions remained during the 2015 El Niño. We examine how this oceanographic variability affected delivery and individual characteristics of larval spotted sand bass (Paralabrax maculatofasciatus) to an estuarine nursery habitat in southern California. To quantify P. maculatofasciatus settlement patterns, three larval collectors were installed near the mouth of Mission Bay, San Diego CA, and retrieved weekly from June–October of 2012–2015. During ‘Blob‘ conditions in 2014 and 2015, lower settlement rates of spotted sand bass were associated with higher sea surface temperature and lower wind speed, chlorophyll a (chl a) and upwelling. Overall, the number of settlers per day peaked at intermediate chl a values across weeks. Individual characteristics of larvae that settled in 2014–2015 were consistent with a poor feeding environment. Although settlers were longer in length in 2014–15, fish in these years had slower larval otolith growth, a longer larval duration, and a trend towards lower condition, traits that are often associated with lower survival and recruitment. This study suggests that future settlement and recruitment of P. maculatofasciatus and other fishes with similar life histories may be adversely affected in southern California if ocean temperatures continue to rise in the face of climate change.

Experimental and field evaluation of otolith strontium as a marker to discriminate between river-spawning populations of walleye in Lake Erie

Otolith microchemistry is a commonly used tool for stock discrimination in fisheries management. Two key questions remain with respect to its effectiveness in discriminating among river-spawning populations. First, do larvae remain in their natal river long enough for their otoliths to pick up that system’s characteristic chemical signature? Second, are larval otolith microchemical differences between natal rivers sufficiently large to overcome spatiotemporal variation in water chemistry? We quantified how larval age, the ratio of ambient strontium to calcium concentrations (Sr:Ca), and water temperature influence otolith Sr in both lab-reared and wild-collected Lake Erie walleye (Sander vitreus). Otolith microchemistry shows promise as a spawning stock discrimination tool, given that otolith Sr in larval walleye (i) is more strongly influenced by ambient Sr:Ca than by temperature; (ii) reflects Sr:Ca levels in the natal environment, even in larvae as young as 2 days old; and (iii) can effectively discriminate between larvae captured in two key Lake Erie spawning tributaries, even in the face of short larval river residence times and within-year and across-year variation in ambient Sr:Ca.

Annual variation in otolith increment widths of walleye pollock (Gadus chalcogrammus) larvae in Funka Bay, Hokkaido, Japan

AbstractTo clarify relationships between year‐class strength and larval growth of walleye pollock (Gadus chalcogrammus), and oceanographic conditions in the Pacific stock off Hokkaido and Tohoku, Japan, we undertook conductivity/temperature/depth (CTD) observations and investigated larval densities, larval otolith increment widths and larval prey densities (of copepod nauplii) of the 2008, 2009, 2010 and 2011 yr classes in Funka Bay. Oyashio Coastal Water (OCW) flowed into the bay in late February in 2008, 2010 and 2011, and the mean water temperatures decreased to 1.9–3.1 °C in March. OCW was not observed in 2009, and it was warm in late February (≥3.4 °C). Increment widths of lapillar otoliths during the yolk‐sac stage were wide in 2009 and 2011, medium in 2010 and narrow in 2008. Increment widths during the first‐feeding stage tended to become wider as the hatch month progressed, and the annual variation during the first‐feeding stage was larger than that of the yolk‐sac stage. The densities of the primary food for the larvae were high in 2008 when larval increment widths were narrowest, so the effect of prey abundance on larval growth appeared to be small. The ranking of the larval abundance in March was nearly coincident with that of the increment width during the larval stage. We, therefore, suggest that the larval growth rate is associated with the mortality rate and that the growth–mortality hypothesis may be applicable to walleye pollock in Funka Bay. Feeding success under warm water conditions may be an important factor that contributes towards high growth rates.

Does otolith chemistry indicate the natal habitat of Newfoundland capelin Mallotus villosus?

Identifying natal origins is important for understanding population structure (e.g. connectivity), but is often difficult to determine for fish with high dispersal potential. Natural tags, such as otolith microchemistry, however, provide the potential to tackle this challenge. Capelin Mallotus villosus is a key marine forage fish that spawns in two distinct habitats in coastal Newfoundland, beach (intertidal, or above low tide zone) and deep-water (15–40m) habitat, where eggs remain throughout incubation. Capelin are predicted to occupy deep-water habitat as temperatures increase at beaches; however, the contribution of deep-water spawning habitat to recruitment is unclear. Here we test whether otolith chemistry differs between field-reared capelin eggs/larvae at beach relative to deep-water habitat on the northeastern Newfoundland coast during July–August 2011–2013. Throughout experimental rearing, we monitored temperature, salinity and trace metals in ambient water. Ambient trace metal concentrations were homogenous across rearing habitats, but beach-reared larval otoliths had significantly lower Ba/Ca, Sr/Ca, Mn/Ca, and Mg/Ca relative to those reared in deep-water. Temperature was consistently higher at beach relative to deep-water rearing habitat (~3–7°C) throughout the experiment, and the partition coefficients of Sr/Ca in larval capelin otoliths (DSr) were negatively related to temperature (log DSr=−0.026 T (°C)+0.907). As salinity and ambient trace metal concentrations did not vary consistently between habitats, these findings suggest that rearing temperature primarily influenced otolith chemistry. Overall, this study reveals the potential to use otolith chemistry in adult capelin to determine the natal (egg) rearing habitat and, thus, the relative contribution of each spawning/rearing habitat to recruitment in future investigations.

Ontogenetic development of the sagittal otoliths of Lipophrys pholis (Blenniidae) during the embryonic, larval and settlement stages

Eggs and settlers of Lipophrys pholis were collected during low tides from a northern Portuguese rocky beach in March and May of 2013. The eggs were reared under controlled-laboratory conditions until the larval stage, while settlers were immediately sacrificed. Sagittae were viewed by scanning electron microscopy to assess the occurrence of different microstructural checks during embryonic, larval and settlement stages. Otoliths recorded several micro-increments (8–10) before hatching in late embryo phases. In larval otoliths a visible hatching check was observed and micro-increments were deposited on a daily basis. Early settlers presented in the otolith edge two types of settlement marks. These findings are important to prevent a misidentification of some life history events and/or to avoid overestimation of individual age from otolith studies.

Offshore–onshore linkages in the larval life history of sole in the Gulf of Lions (NW-Mediterranean)

Understanding individual dispersion from offshore natal areas to coastal nurseries during pelagic larval life is especially important for the sustainable management of exploited marine fish species. For several years, the hatching period, the larval life duration, the average growth rate and the otolith chemical composition (δ13C, δ18O, Sr:Ca and Ba:Ca) during the larval life were studied for young of the year (YOY) of sole collected in three main nurseries of the Gulf of Lions (GoL) (Thau, Mauguio and Berre). We investigated the spatial variation in the origin of the sole larvae which colonised the nurseries around the GoL, and whether temporal differences in environmental conditions during this life stage affected growth and larval life duration. The hatching period ranges from October to March, depending on year and site. Average ages at metamorphosis varied between 43 and 50 days, with the lowest and highest values consistently found for Mauguio and Berre, respectively. Otolith growth rates ranged between 2.7 and 3.2 μm d−1, with the lowest values in Thau and Mauguio and the highest in Berre. Otolith chemical composition during the larval life also varied, suggesting contrasted larval environmental histories in YOY among nurseries. In fishes from Berre and Mauguio, larval life was more influenced by the Rhône River, showing consistently higher larval Ba:Ca ratios (10/23 μmol mol−1) and lower δ13C (−6.5/−6.1‰) and δ18O values (−1.6/0.1‰) than for Thau (with Ba:Ca ratios < 8 μmol mol−1, δ13C ∼−2.3‰ and δ18O ∼1.5‰). Differences in larval otolith composition were observed for 2004, with higher Ba:Ca and lower δ13C and δ18O values than in the two other years. These differences were explained by changes in composition and chemical signatures of water masses after an exceptional flooding event of the Rhône River in late 2003.

Osmotic induction improves batch marking of larval fish otoliths with enriched stable isotopes

Abstract Otolith marking with enriched stable isotopes via immersion is a recent method of batch marking larval fish for a range of research and industrial applications. However, current immersion times and isotope concentrations required to successfully mark an otolith limit the utility of this technique. Osmotic induction improves incorporation and reduces immersion time for some chemical markers, but its effects on isotope incorporation into otoliths are unknown. Here, we tested the effects of osmotic induction over a range of different isotope concentrations and immersion times on relative mark success and strength for 26Mg:24Mg, 86Sr:88Sr and 137Ba:138Ba on Atlantic salmon (Salmo salar) larvae. 71% and 100% mark success were achieved after 1 h of immersion for 86Sr (75 µg L−1) and 137Ba (30 µg L−1) isotopes, respectively. Compared with conventional immersion, osmotic induction improved overall mark strength for 86Sr and 137Ba isotopes by 26–116%, although this effect was only observed after 12 h of immersion and predominately for 86Sr. The results demonstrate that osmotic induction reduces immersion times and the concentrations of isotope required to achieve successful marks. Osmotically induced isotope labels via larval immersion may prove a rapid and cost-effective way of batch marking fish larvae across a range of potential applications.

How Much Cleaning is Needed When Processing Otoliths from Fish Larvae for Microchemical Analysis?

AbstractOtolith microchemistry is a widely used tool in fish ecology and fisheries management. Cleaning‐protocol assessments are lacking, however, especially for larval fish otoliths, which are more fragile and difficult to manipulate than larger otoliths. Herein, we assess the value of cleaning larval fish otoliths with sonication, a commonly used technique that is time consuming and risks loss or breakage of small otoliths, as well as with a lesser‐known technique using a low‐power laser cleaning pulse (LPLCP). We measured trace elements in larval Walleye Sander vitreus reared in different water strontium concentrations. Strontium and Ba did not differ among any cleaning treatments, indicating that neither sonication nor a LPLCP is necessary. Likewise, Mn did not differ between sonicated and nonsonicated treatments; however, Mn was lower when a LPLCP was used. We suggest omitting the sonication step when preparing otoliths for trace element analysis of Sr, Ba, Mn, and other trace elements found in high abundances. The addition of a LPLCP is useful, although more research in this arena is warranted. Our findings should greatly reduce otolith processing time and the risk of losing and breaking larval otoliths during the cleaning process.

Integrating multiple bioassays to detect and assess impacts of sublethal exposure to metal mixtures in an estuarine fish

Estuaries are natural sinks for a wide range of urban, industrial and agricultural contaminants that accumulate at potentially toxic but non-lethal concentrations, yet we know relatively little about the long-term impacts of toxicants at these levels on aquatic organisms. In this study, we present an integrated, multi-pronged approach to detect and assess the impacts to estuarine fish of exposure to sublethal concentrations of metal mixtures. Our aims were to (1) examine the effects of sublethal metal exposure on the embryonic development of Galaxias maculatus, an estuarine spawning fish native to southeastern Australia, (2) determine whether sublethal exposure during development has knock-on effects on larval behaviour, and (3) establish whether a signature of metal exposure during embryogenesis can be detected in larval otoliths (“ear bones”). G. maculatus eggs are fertilised in water but develop aerially, in direct contact with estuarine sediments. We were thus also able to explore the relative importance of two exposure pathways, water and sediment. Embryos were exposed to two concentrations of a metal mixture containing Cu, Zn and Pb in water (during fertilisation) and on spiked sediments (during development), using a fully crossed experimental design. Overall, we found that exposure to the metal mixture reduced embryo survival and slowed embryonic development, resulting in poorer quality larvae that exhibited a reduced phototactic response. Differences in exposure to metals between treatment and control embryos were also permanently recorded in the developing otoliths. Combined these three approaches have the potential to be a powerful novel bioassessment tool as they provide a means of identifying a history of metal exposure during the embryonic period and linking it to suboptimal early growth and performance traits which could have long term fitness consequences.

Longevity in maternal transmission of isotopic marks in a tropical freshwater rainbowfish and the implications for offspring morphology

Transgenerational marking is increasingly being used to study the early life history, biology and ecology of fishes. However, the timeframe over which the injected enriched stable isotopes remain in the mother and are passed onto her offspring is largely unknown. Similarly, we have relatively little knowledge of the effects of isotope labelling on the morphology of offspring. In this study, we injected adult female eastern rainbowfish (Melanotaenia splendida) with two doses (20 µg g–1 and 40 µg g–1) of enriched 137Ba or 87Sr stable isotopes to mark the otoliths of their larvae and examine the effects of isotope labelling on larvae morphology. Isotope ratios in larval otoliths were significantly different from controls in larvae hatched up to 174 days post-injection, indicating that enriched isotopes can mark the larvae of this daily spawning species up to 6 months after a single injection. Isotope-marked larvae displayed variable, but generally increased physical size, indicating that enriched stable isotope labelling may have some unintended effects on larvae morphology. Consequently, transgenerational marking provides a long-term tool for marking the offspring of M. splendida to disentangle their patterns of survivorship and dispersal, with the caveat that such studies should be interpreted in light of potential isotope-related changes in offspring morphology.

Using otolith trace elements as biological tracer for tracking larval dispersal of black porgy, Acanthopagrus schlegeli and yellowfin seabream, A. latus among estuaries of western Taiwan

To understand if the trace elements in the otoliths can be used as a biological tracer for tracking natal origin and dispersal of larval black porgy (Acanthopagrus schlegeli) and yellowfin seabream (A. latus) among estuaries, the fish larvae in 1997, 1998, and 2005 and water samples in 2005 were collected from 3 estuaries on the western coast of Taiwan. The elemental composition in both otoliths of the larvae and water samples were analyzed by a solution-based inductively coupled plasma mass spectrometer (ICP-MS). Temporal and spatial differences were found in some of the measured 12 element/Ca ratios in the larval otoliths. The water elemental composition was also significantly different between estuaries and between flood and ebb tides. 87.5–100 % of the larvae of both species could be successfully assigned to their sampled estuaries. However, only 20 % of the black porgy collected from TT in 1998 could be successfully assigned to TT and the rest to GST and TK. The low assignment might be due to the mixing by the tidal current because the flood tide comes from the direction of TK in the south and GST in the north and merged in the middle of Taiwan Strait nearby TT. This study demonstrated that the trace elements in the otoliths of the fish have the potential to detect the temporal and spatial variation of environmental conditions in the estuaries and subsequently can be used for tracking the origin of the larvae from different estuaries and their dispersal rate.

Retention of a transgenerational marker (137Barium) in tissues of adult female anemonefish and assessment of physiological stress

Recently it was shown that female fish injected with enriched stable isotopes maternally transmit a chemical signature to larval otoliths. Validation of this larval marking technique requires laboratory experiments to determine appropriate injection concentrations and to assess any negative effects on larval and adult condition. This study investigated the temporal profile of 137barium assimilation and retention in tissues of adult female anemonefish Amphiprion melanopus (Pomacentridae) following intraperitoneal injection with either 2 or 4 μg 137Ba g−1 body mass. Mean barium isotope ratios (138Ba:137Ba) in the two groups of treated fish were not significantly different from each other, but were significantly different from those in the control group up to 56 days post-injection. This pattern of 137Ba retention was consistent across gonad, muscle, liver and bone tissues. Mean plasma cortisol concentration (an indicator of non-specific physiological stress) was not significantly different among groups and was considered to be representative of unstressed fish. Together, these results indicate that (1) A. melanopus suffer minimal physiological stress and cope well after treatment with 137Ba, (2) 137Ba is retained in female A. melanopus for a prolonged period (at least 56 days), such that multiple clutches of offspring are likely to be marked with an isotopic signature, and (3) a lower dosage of 2 μg 137Ba g−1 appears sufficient for transgenerational marking. It is concluded that 137Ba is suitable for use as a transgenerational marker and is a powerful tool to resolve long-standing enigmas such as larval dispersal distances and the fishery benefits of marine reserves.

Determining Mark Success of 15 Combinations of Enriched Stable Isotopes for the Batch Marking of Larval Otoliths

AbstractChemical marking of otoliths via immersion in solutions of enriched stable isotopes provides a means of distinctively marking large batches of hatchery‐produced fish. Four enriched stable isotopes (barium: 137Ba and 138Ba; strontium: 88Sr; magnesium: 24Mg) were used individually and in combination to determine mark success and the ability to correctly classify 15 unique batch marks in the otoliths of larval Murray cod Maccullochella peelii. Marking with the enriched stable isotopes 137Ba, 138Ba, and 88Sr (individually or in combination) produced clear and distinctive marks (98% mark success) with 93% of fish correctly classified to their respective isotope mark. Despite exposure of the fish to an altered Mg isotope ratio in the water, a corresponding shift in the otoliths was not observed (8% mark success), and many 24Mg‐enriched fish were misclassified. Due to the low cost and minimal effects on hatchery protocols, the use of Sr and Ba isotopes to mark hatchery‐reared fish at the larval stage has the potential to be a powerful tool in the production and management of a wide range of fish species.Received February 25, 2011; accepted May 22, 2011