Richard L. Radtke

Age at recruitment of Hawaiian freshwater gobies

SynopsisVery little is known about the dynamics of native Hawaiian stream fishes. Five species are restricted, as adults, to freshwater streams and estuaries on the major islands of the Hawaiian archipelago. This paucity of information is partly due to difficulties inherent in determination of age and subsequent determinations of life history characteristics. In the present study, we determined the age of newly recruited Hawaiian gobies,Stenogobius genivittatus andAwaous stamineus using otolith microtechniques. Internal otolith increments were enumerated using scanning electron microscopy (SEM). Increments of newly recruited juveniles were deposited on a daily basis as validated through a marking study. Results showed recruitment at an average age of 135 and 161 days for these two species, respectively, with more rapid growth following recruitment to freshwater. Chemical analyses of otolith carbonate of the Hawaiian gobies by electron microprobe for strontium and calcium concentrations provided valuable insights into a fishs past history. A combination of structural and chemical analyses makes it possible to link growth and recruitment to nutritional and environmental factors. Such information developed as a broad model would be applicable to the management of Hawaiian gobies and would greatly improve the quality of information available for these unique fish populations and other fish populations

Strontium-calcium concentration ratios in fish otoliths as environmental indicators

1. n1. External and internal examinations of otoliths in fishes for macrostructure and microstructure has demonstated yearly, daily and population rhythmic patterns. n n2. n2. Chemical analyses (atomic absorption) of otolith carbonate from reared Fundulus heteroclitus for strontium-calcium concentration ratios demonstrated changes in chemistry related to temperature. n n3. n3. Microprobe analyses made it feasible to interpret almost daily changes in temperature to provide the temperature history of an individual fish. n n4. n4. A combination of microprobe analyses and daily increment analyses of otoliths can provide a life history profile for individual fish and can provide information on the environmental history of each fish. n n5. n5. Such information is vital to our understanding of the processes underlying recruitment and growth rates, and would make it possible to link growth and mortality rates to environmental occurrences.

Strontium:calcium ratios in juvenile Atlantic herring Clupea harengus L. otoliths as a function of water temperature☆

The effect of environmental temperature on the atomic concentration ratios of strontium to calcium in fish otoliths was investigated for young-of-the-year juvenile Atlantic herring Clupea harengus L. which were captured from the wild and held in the laboratory for 1 yr. The fish were maintained in large volume, flowing seawater tanks and were subject to the seasonal temperature cycle of Maine coastal waters (≈ 2–18°C). Otolith Sr/Ca ratios were measured for 136 fish and related to temperature by a hyperbolic Michaelis-Menten function. The greatest temperature effect occured at lower temperatures, where Sr/Ca ratios increased with decreasing temperature. There was less of an effect at warmer temperatures where the Sr/Ca ratios approached an asymptote. The results are interpreted in terms of the effect of environmental temperature on the physiological processes that result in a discrimination against the passage of strontium from seawater into the saccular endolymph which baths the otoliths. We suggest that at lower temperatures, where those physiological processes become slowed or impaired, strontium passes more readily into the endolymph and becomes incorporated into the otolith aragonite, thus supporting the use of otolith Sr/Ca ratios in studies of life histories of fishes at environmental extremes.

Environmental information stored in otoliths: insights from stable isotopes

The present study compares the stable oxygen-and carbon-isotope ratios (180:16O;13C:12C) in the otoliths of Atlantic cod,Gadus morhua, with those expected at equilibrium with seawater. Otoliths from juveniles reared for a 3 mo period under controlled conditions indicate that otoliths are formed in isotopic disequilibrium with seawater. This is probably due to positive metabolic fractionating of the heavier isotopes. This “vital effect” remains constant over the temperature range studied here (9 to 16°C) but may differ among other species. Our data indicate that the concentration of18O in calcium carbonate is inversely related to temperature and is described as ∂18Oa − ∂w − 3.79 − 0.200(T°C). The13C:12C ratios of otoliths and body tissues are related to the carbon ratio in the food source, although we found that the13C concentration is considerably higher in the otoliths relative te, the body tissues and the diet.

Evidence of a Marine Larval Stage in Endemic Hawaiian Stream Gobies from Isolated High-Elevation Locations

Abstract Tropical streams on high oceanic islands are characterized by populations of amphidromous gobioid fishes. Adult fish live and breed in freshwater and many spawn at high (>300 m) elevations. Newly hatched fry are swept down to the sea where they develop for a period of time before recruiting to a stream. In analogous habitats in other geographic areas, amphidromous populations have further evolved into landlocked forms (i.e., populations that spend their entire life cycle in freshwater). We analyzed depositional patterns of trace elements in the otoliths of adult Lentipes concolor, an amphidromous goby endemic to Hawaii, to determine whether landlocked forms occurred. Otoliths were obtained from fish collected from the Hawaiian stream habitats most likely to harbor landlocked populations—upper elevations of interrupted streams and sections of streams above high waterfalls. A transition from a marine phase to freshwater existence was demonstrated as a decrease from high to low strontium : calcium r...

Stable isotopic investigation of physiological and environmental changes recorded in shell carbonate from the giant clam Tridacna maxima

The aragonitic shell of the photosymbiont-bearing bivalve Tridacna maxima contains a record of the physiological and environmental changes the organism has experienced during its lifetime. This record is preserved as chemical and microstructural variations throughout the shell. Stable isotopic analyses of oxygen (18O/16O) and carbon (13C/12C) in shell carbonate were combined with growth increment studies to interpret the shell record of specimens collected from the Rose Atoll (Lat. 14°31′S; Long. 168°10′W) in April 1982. The seasonal water temperature cycle is recorded in the oxygen isotopic signature of the clams, permitting the recognition of annual cycles in the δ18O profile. The total number of these cycles corresponds to the age of a specimen, while the cycle length is a measure of the yearly growth rate. Large-amplitude cycles, reflecting year-round calcification, characterize the early portion of the growth record. With the onset of sexual maturity and slower growth at an age of approximately ten years, the cycles decrease in amplitude and become more erratic. During this later growth phase calcification is limited to the cooler months of the year, perhaps in response to a re-ordering of energy priorities between growth and gametogenesis. A growth curve developed from the δ18O profile indicates rapid juvenile shell growth followed by slower growth thereafter producing a lifespan of several decades. Carbon isotopic analyses of T. maxima were compared to analyses of the symbiont-barren gastropod Terebra areolata collected from the same locality in April 1984. A 2‰ depletion in the δ13C composition of T. maxima shell carbonate is attributed to a symbiontenhanced metabolic rate and an increased flow of isotopically light, respired CO2 into the carbon pool used in calcification. Such a depletion may prove useful in identifying the presence of photosymbionts in extinct species of fossil mollusks.

Formation and structural composition of larval striped mullet otoliths

Abstract The otoliths of larval fish may be useful data-storage systems if the mechanisms of formation and carbonate deposition are discerned. Striped mullet Mugil cephalus were reared from hatching under controlled laboratory conditions. The start and periodicity of otolith growth increments were examined by light and scanning electron microscopy, and ratios of stable isotopes in otolith carbonate were determined. Otoliths formed their first increment 1 day after the larvae hatched and increment formation continued on a daily schedule regardless of growth rate. Electron microscopy revealed a transition area in otoliths that corresponded to the time of yolk-sac absorption. Isotopic analyses showed that otolith carbonate is deposited in disequilibrium with the ambient water chemistry, in contrast to prevailing theory.

Reproduction of the Antarctic fish Nototheniops nudifrons

The reproductive biology of the Antarctic fish Nototheniops nudifrons (Lönnberg, 1905) was analyzed by examination of the gonads of fish collected in March and April 1985 in trawls near Low Island, Antarctic Peninsula, and compared to direct observations of reproduction and early larval development in the laboratory from March to October of the same year. Males and females reached sexual maturity at an age of 4 to 5 yr. Mature males differed in coloration from females and immature males. Ovaries of sexually mature females contained two distinct size modes of vitellogenic oocytes, representing two separate clutches of developing eggs. Females spawned 100 to ∼ 3 500 demersal eggs, which were laid in a nest in crevices or under rocks, and guarded by the male for about 4 mo. Females did not assist in nest defense or egg care. Most spawning in the field and in the laboratory occurred in late fall and early winter (May to June). A second clutch may be spawned in spring (November and December). Eggs hatched after 124 d, and larvae were raised for 38 d. Otoliths of larvae contain internal microincrements, which are deposited in a daily fashion, and are visible by light microscopy. The otoliths of 32 adult fish were examined by scanning electron microscope, and counts of microincrements in these otoliths allowed the backcalculation of hatching dates. Estimated hatching dates were between September and May.

The stable isotopic composition of bluefin tuna thunnus thynnus otoliths evidence for physiological regulation

Abstract 1. 1. The stable isotopic composition of giant (>350kg) bluefin tuna ( Thunnus thynnus ) was determined for fish held under known environmental conditions where gut temperatures were monitored. 2. 2. It was discovered that otolith stable isotopes were not deposited in equilibium with hydrographic conditions. 3. 3. The oxygen isotopic composition appeared to be a function of body and brain temperature, which was regulated through a thermoregulatory mechanism. 4. 4. The depletion of 13 C in the otoliths established that the carbon isotopic composition of the otolith aragonite was fractionated by metabolic processes. 5. 5. These findings suggest that it is possible to study the physiological history of bluefin tuna and maybe other fish species through the use of the stable isotopic composition of otoliths.

Age and growth information available from the otoliths of the Hawaiian snapper, Pristipomoides filamentosus

The otoliths of tropical fish may provide important life history information incorporated within their structural and chemical constituents. All three otoliths (sagitta, lapillus, asteriscus) of the tropical fish Pristipomoides filamentosus were examined internally by Scanning Electron Microscope methods to observe micro-increments and externally to determine three dimensional structure. It was discovered that the sagitta contained four cores and that the plane chosen to be sectioned for micro-increment enumeration could result in errors if more than one core were transversed. The medial cross sectional plane was consequently resolved to effer the most accurate micro-increment counts. Obserations of lapilli also revealed micro-increments and subsequent counts were closely correlated to those detected in the sagittae. The visualization of increments made it feasible to assess age and evolve a growth model. In addition, sagitta weight was found to be related to growth rate and may provide a quick estimate of relative growth. Chemical analyses of otoliths for stable isotopes and Sr/Ca ratios all suggested that an individual fish inhabited warmer waters as it became older. A combination of otolith structural and chemical information can provide age and growth data which is essential to the calculation of accurate population parameters.