Delta Smelt (Hypomesus transpacificus) Exhibit Wide Variation in Spawning Behavior: An Investigation of Substrate Type, Diel Timing, and Participants

Studies of cultured populations can be invaluable to the conservation of imperiled species for which little is known and whose very low abundance in the wild can preclude studies with robust sample sizes. For example, in endangered delta smelt (Hypomesus transpacificus), conservation measures developed to mitigate population decline are hindered by a lack of knowledge regarding spawning behavior. However, the availability of a cultured population allows important questions about spawning to be addressed experimentally. We examined the effect of substrate type on spawning behavior and egg fertilization success in cultured H. transpacificus under laboratory conditions. We also examined the diel frequency of spawning and the sex and number of spawning participants. We found that the frequency of spawns and resulting egg fertilization success did not differ between sand, gravel, and control (acrylic) substrates. We also demonstrated that spawning was predominantly nocturnal, though rare diurnal spawns were observed. Of the five mature males and five ripe females available within a given trial, spawns included up to seven participants, but most frequently occurred between a single female and one or two males. Our results highlight the wide behavioral variation exhibited by H. transpacificus during spawning, particularly in terms of substrate use, diel timing, and participants. These findings provide the most detailed and experimentally robust data regarding H. transpacificus spawning behavior to date and thereby provide ongoing conservation efforts with much-needed information.

Observation on the reproductive behavior and embryo of the daisy’s ricefish, Oryzias woworae in laboratory condition

Oryzias woworae is an endemic ricefish from Muna Island, Southeast Sulawesi, traded as an ornamental fish. Information on the biology of these fish is very lacking, including their reproductive. These fish also face the threat of population decreasing in the wild. The research aimed to examine the spawning behavior and embryonic of O. woworae as the basis for aquaculture. Fish spawning was carried out using 1 male: 1 female ratio, which was repeated three times. The observed spawning behavior was pre-spawning, mating process, egg number, and morphology. Behavioral observations were carried out for five days of spawning. Observation of embryos was carried out to see the stages of embryo development until hatching. The results obtained on pre-spawning behavior were changes in body color and blackened fins in males, which did not occur in female fish. Males actively swim by approaching their dorsal and anal fins while chasing females. The female releases the eggs and is attached to the substrate, rapidly fertilized by the male fish. There is a phenomenon of females carrying eggs on the genital pore before being released to the substrate (non-pelvic brooder). Spawning only occurs during the day, and spawning is getting faster, which is at 09:00 AM on the fifth day. Oryzias woworae eggs have a diameter of 1.3 ± 0.2 mm, equipped with attaching and non-attaching filaments. Observations of O. woworae embryos showed that embryo hatching occurred at seven days 23 hours post-fertilization.

The importance of spawning behavior in understanding the vulnerability of exploited marine fishes in the U.S. Gulf of Mexico

The vulnerability of a fish stock to becoming overfished is dependent upon biological traits that influence productivity and external factors that determine susceptibility or exposure to fishing effort. While a suite of life history traits are traditionally incorporated into management efforts due to their direct association with vulnerability to overfishing, spawning behavioral traits are seldom considered. We synthesized the existing biological and fisheries information of 28 fish stocks in the U.S. Gulf of Mexico to investigate relationships between life history traits, spawning behavioral traits, management regulations, and vulnerability to fishing during the spawning season. Our results showed that spawning behavioral traits were not correlated with life history traits but improved identification of species that have been historically overfished. Species varied widely in their intrinsic vulnerability to fishing during spawning in association with a broad range of behavioral strategies. Extrinsic vulnerability was high for nearly all species due to exposure to fishing during the spawning season and few management measures in place to protect spawning fish. Similarly, several species with the highest vulnerability scores were historically overfished in association with spawning aggregations. The most vulnerable species included several stocks that have not been assessed and should be prioritized for further research and monitoring. Collectively, the results of this study illustrate that spawning behavior is a distinct aspect of fish ecology that is important to consider for predictions of vulnerability and resilience to fisheries exploitation.

SPAWNING OF BLACK GHOST KNIFEFISH, Apteronotus albifrons WITH DIFFERENT SEX RATIOS

Black ghost knifefish, Apteronotus albifrons, is a South America-introduced ornamental fish species that has been widely cultivated in Indonesia. Some farmers breed this fish with different sex ratios, but the optimum sex ratio remains unclear. This study aimed to evaluate the spawning behavior and reproductive performance of black ghost knifefish with different sex ratios. The treatments in this study were arranged in a completely randomized design consisting of different sex ratios between males and females, namely: A (one male : three females), B (two males : three females), and C (three males : three females). Each treatment was done in triplicate. The broodstock were maintained in an aquarium (80 cm x 40 cm x 40 cm) and fed with bloodworm twice a day. The water was changed every day as much as 60% of the total volume. During the experiment, the parameters of spawning behavior, number of fish spawning, number of eggs, fertilization rate, hatching rate, and daily spawning frequencies were observed. The observation was done for seven days. The study results showed that black ghost knifefish spawned at night (11 pm - 2 am). The mating and spawning occurred between one male and one female. Competition between males was observed in the treatments indicated by aggressive movements of a male toward the others, such as sudden approaching, chasing, and driving away the others. Fish in treatment-B spawned consistently from day-1 to day-5. Fish in treatment-A spawned from day-2 to day-4, while fish in treatment-C spawned only on day-7. The reproductive performance parameters showed no significant difference in all treatments except the hatching rate parameter of treatment-B. The study concludes that better reproductive performance of black ghost knifefish, A. albifrons can be achieved with a spawning ratio of two males and three females. Further research on individual and mass spawning methods with the best spawning ratio of the fish is required.

A possible stimulus to induce SPAWNING in Ezo abalone Haliotis discus hannai during stormy weather: Fenton reaction induces spawning behavior

Synchronous spawning is an important behavior to increase fertilization success of invertebrates with external fertilization. Previous work has shown that it is possible to induce spawning behavior using free radicals in tank experiments, but the stimulus for spawning in the wild is not fully understood. Ezo abalone Haliotis discus hannai mainly spawn during stormy weather. Rainwater contains H2O2 and iron (II) ions (Fe2+). We propose that during stormy weather water layers in the ocean are mixed and the surface layer containing H2O2 and Fe2+ interacts with the ocean bottom; this leads to conditions suitable for the Fenton reaction to occur. Hydroxyl radicals (·OH) are generated during the oxidization of Fe2+ by H2O2 and we hypothesized these induce spawning behavior of abalone in the wild. This study observed that H. discus hannai released eggs after salinity decreased due to the rainfall during stormy conditions. In addition, our tank experiment demonstrated that ·OH generated by the Fenton reaction induced synchronous spawning behavior between the sexes. This study provides a new hypothesis about control of synchronous spawning in H. discus hannai and the results could be applicable to other invertebrates.

La distribución del ictioplancton está directamente relacionada con la hidrodinámica de una región y el comportamiento de desove de los adultos. En este estudio buscamos mapear las zonas de mayor ocurrencia de ictioplancton observadas en la Bahía de São Marcos, que tiene una de las mayores amplitudes de marea en la Costa Amazónica, Brasil. El ictioplancton fue recolectado mediante una técnica de arrastre horizontal en la capa superficial, utilizando una red de rodillos cónicos con malla de 300 μm acoplada a un medidor de flujo, para estimar el volumen de agua filtrada en la Bahía de São Marcos (Complexo Estuarino de São Marcos - CESM, Maranhão) . La densidad se calculó a partir de la relación entre el número total de huevos y larvas en cada muestra y el volumen de agua filtrada. Las fuentes de Ictioplancton se consideraron continuas y se organizaron para representar de forma asincrónica las condiciones de distribución. Para ello se realizó utilizando el polígono de Voronoi para determinar la forma espacial del área de operación de todos los puntos de muestreo. El uso de CESM, como lugar de desove y cría de larvas de peces, se verificó en todas las épocas del año, con mayor densidad de huevos en la época de lluvias y mayor densidad de larvas durante la época seca. La ubicación de las mayores densidades de ictioplancton varió, con las concentraciones más altas más cerca del canal sureste del CESM en la estación seca, moviéndose hacia el centro en la estación lluviosa. El canal sureste del CESM era, por tanto, un área de cría de muchas especies de peces, lo que requería una acción prioritaria para la protección del medio ambiente.

The occurrence of ichthyoplankton is associated to the hydrodynamics and spawning behavior of adults. In this study we aimed to detect regions of concentration of ichthyoplankton in São Marcos Bay, which has macro tidal amplitudes in Amazon Coast, Brazil. Ichthyoplankton was acquired by way of drag technique, using with 300 μm mesh. The density was obtained considering the number of eggs and larvae in filtered water. The sources of Ichthyoplankton were defined continuous and organized to denote the asynchronously the distribution conditions. To this was done using Voronoi polygon to determine the spatial shape of the region of operation of all sampling points. The use of CESM, as a spawning site and breeding fish larvae, was verified at all times of the year, with a higher density of eggs in the wet period and a higher density of larvae during the dry period. The position of the higher ichthyoplankton densities varied, considering concentrations in the area at south-east channel of the CESM in the rainless period, going to the central area in the wet period. The southeast of CESM is, therefore, a nursery for fish, requiring environmental management actions.