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Determining the timing and location of spawning is critical for the conservation and management of aquatic species. Environmental DNA (eDNA) analysis can be used to monitor fish spawning activity by detecting peaks in eDNA concentrations and nuclear DNA (nuDNA)/mitochondrial DNA (mtDNA) ratios; however, the duration and diffusion distance of high concentrations of eDNA produced by spawning activities in water bodies are still unknown, preventing us from making accurate and effective survey plans to monitor spawning activities. Using common carp as a target species, we conducted artificial spawning experiments to investigate the spatiotemporal changes in eDNA concentrations during spawning. The results showed that the nuDNA concentration, mtDNA concentration, and nuDNA/mtDNA ratio that were increased by spawning activity decreased at rates of 7.78 %, 5.22 %, and 2.56 %, respectively, per 0.1 h after reaching the peak. Data simulations were performed to estimate the probability of successful monitoring of carp spawning activity during repeated sampling at different times and distance intervals. The results showed that carp spawning activity over the past 24 h could be monitored by eDNA analysis. Additionally, when carp spawning activity occurs once, spawning activity can be successfully monitored by measuring the nuDNA concentration or the nuDNA/mtDNA ratio with a probability of approximately 50–75 % based on a sampling plan of sample collection every 100 m and every 24 h. Thus, the spawning activity of aquatic species can be estimated with high spatial and temporal accuracy using eDNA analysis.

Artificial fertilization of cultured fish is essential for seed production using breeding techniques. However, in tuna species, the success rate of artificial fertilization is tremendously low. In this study, it was reported that the adequate procedure for ovulated egg collection and storage for artificial fertilization in kawakawa Euthynnus affinis. The collection of ovulated eggs was attempted using new techniques that disrupt only spawning activity without discontinuing ovulation. The available time to use ovulated eggs was also examined by assessing the optimal preservation process and temperature. As a result, artificial fertilization was effectively executed by assessing spawning time and thoroughly extracting ovulated eggs immediately after ovulation, with a success rate of 70% and an ovulation rate of 51.7%. Ovulated eggs could be stored with small quantities of ovarian fluid to sustain fertility. However, fertility was better preserved with Hanks' solution. Ovulated eggs with high productivity were achieved 3 h after egg extraction when maintained in Hanks' solution at 20 °C, leading to a supply of one-cell stage embryo for microinjection treatment constantly by continuously executing artificial fertilization. This systematic procedure permitted selective breeding by 1:1 mating between top-quality parental fish and applying several developmental engineering techniques to kawakawa breeding. [ABSTRACT FROM AUTHOR]

Horseshoe crab populations are declining worldwide, and Tachypleus tridentatus (Leach, 1819) has recently been classified as Endangered in the IUCN Redlist. Among the keys for species survival is successful reproduction. Although there are reports on the reproduction, particularly details on the spawning behaviour, of the American species, Limulus polyphemus (Linnaeus, 1758), information on Southeast Asia species is very scant. This field study reports the nesting activities of T. tridentatus at Jambongan Island, Sabah, Malaysia. Observation were carried out on 16 spawning pairs that were spotted during full and new moon from April-July 2016 in Sabah. Nest placements, number of nests, number of eggs, time spent at each nest, and nest widths, depth, and distance from the highest tide line were recorded for each pair. Tachypleus tridentatus generally laid an average of 967 ± 54.1 eggs/nest (171–2,282) in as many as nine nests on the intertidal zone between 125 and 940 cm from the highest tide. The first nest was dug once the tide began rising, followed by the consecutive nests towards the highest tide line with nest depths ranging between 13 and 22 cm. The complete spawning session (first nest to the last) ended in less than two hours. Time spent in spawning correlates positively with the number of nests and the total number of eggs laid by each spawning female. The spawning area, which is made up mainly by fine and medium-size sediment grains, also experience stable temperature, salinity, and dissolved oxygen conducive for egg-laying and larval development for successful reproduction. The details of spawning are important for planning successful future conservation initiatives for the species, especially in tropical regions. [ABSTRACT FROM AUTHOR]

Chinese sturgeon ( Acipenser sinensis) is the flagship species of the Changjiang River. The migration route of this species is blocked by the first dam, the Gezhou Dam, and its reproduction is affected by the Three Gorges Dam (TGD), one of the largest dams in the world. We studied the impact of the impoundment of the Three Gorges Reservoir (TGR) since 2003 on the spawning stock and the natural reproduction of the Chinese sturgeon by using our monitoring data from 1997 to 2013. Results indicate that TGR impoundment has delayed the first spawning dates of the fish from middle-late October to late November, decreased the amount of spawning activities from twice to only once each year, and significantly reduced egg production. In particular, the fish did not demonstrate any spawning activities in 2013. Therefore, TGR impoundment significantly affects the natural reproduction of the fish downstream of the TGD. The spawning stock size of the fish is also predicted to further decrease in the future, which will lead to a risk of population extinction. Ecological regulations must be imposed on decreasing the water temperature to 20°C before mid-October and increasing water discharge downstream of the TGD in October to induce spawning of the Chinese sturgeon. [ABSTRACT FROM AUTHOR]

Spawning behaviour of Alosa alosa was observed by high resolution imaging sonar. Detected clouds of sexual products and micro bubbles served as a potential indicator of spawning activity. Peak spawning time was between 0130 and 0200 hours at night. Increasing detections over three consecutive nights were consistent with sounds of mating events (bulls) assessed in hearing surveys in parallel to the hydro acoustic detection. In 70% of the analysed mating events there were no additional A. alosa joining the event whilst 70% of the mating events showed one or two A. alosa leaving the cloud. In 31% of the analysed mating events, however, three or more A. alosa were leaving the clouds, indicating that matings are not restricted to a pair. Imaging sonar is suitable for monitoring spawning activity and behaviour of anadromous clupeids in their spawning habitats. [ABSTRACT FROM AUTHOR]

The scientific literature on population dynamics, breeding biology and nesting behaviour of the Asian horseshoe crabs is limited and still to emerge from several locations in South and Southeast Asia. The present study (2009–2011), aimed at observing the spawning activity of Tachypleus gigas (Müller, 1785) in relation to local environmental conditions, was carried out from Tanjung Selangor (Sites 1–3) on the east coast of Peninsular Malaysia. Southwest (SW) monsoon (May–September) was found to be more favourable (range, 456–1309 eggs) than Inter-monsoon (IM) (April and October) (169–317 eggs), whereas no eggs at the time of Northeast (NE) monsoon (November–March). Meanwhile, T. gigas preferred Site-1 (located close to River Pahang mouth) for its nesting in the SW and shifted to Site-2 and/or Site-3 (located 150–200 m interior) in the IM periods. This nest shifting behaviour of T. gigas was primarily associated with the seasonal water current that becomes intensive during NE monsoon. However, the human activities such as sand mining (2010), jetty (2010–2011) and road/bridge (2011 – present) constructions in the vicinity have affected the normal physicochemical conditions of the sediment/water. Importantly, the sediment being represented largely by medium sand with moderate sorting, symmetrical and very leptokurtic properties in 2009 was changed into coarse sand with poor sorting, fine/very fine skewed and extremely leptokurtic in 2010–11. In addition, the heavy metal contamination of Cadmium and Selenium in the sediment and Hydrogen Sulfide in the water increased considerably (2010–11). These changes, not only reduced T. gigas spawning activity/egg counts between 2009 and 2010 (from an average of 912 ± 690 to 360 ± 288) (±SD), but also correlated with its total absence during 2011 (PRIMER v .6). Since Tanjung Selangor beach (adjoining the Terus and Pahang Tua estuary) is one of the very few known spawning grounds for the Malaysian horseshoe crab ( T. gigas ), it is imperative to conserve and manage this area and it should be sanctioned as a ‘Marine Protected Area’. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) analysis holds great promise as an efficient and noninvasive method to monitor not only the distribution of organisms but also their spawning activity. In eDNA analysis-based monitoring of spawning activity, the detection of sperm-derived eDNA is a key point; however, its characteristics and dynamics are completely unknown. The present study focuses on the persistence and particle size distribution (PSD) of eDNA derived from the sperm of Japanese jack mackerel. First, we investigated the time-dependent degradation and the PSD of sperm-derived eDNA by artificially adding sperm to seawater. Next, we kept fish in tanks and examined the changes in eDNA concentration and PSD before and after spawning. The results of two experiments showed that the degradation of sperm-derived eDNA proceeded rapidly, with PSD shifting to a smaller size regardless of the DNA region (Cyt b or ITS1). Additionally, it was shown that the nuclei and mitochondria released from sperm through degradation had a size distribution that was not simply dependent on each organelle size. These results will contribute to elucidating the characteristics and dynamics of eDNA specifically during the spawning season and to further developing eDNA analysis as a powerful tool for the monitoring of spawning activity.

ABSTRACT Chum salmon ( Oncorhynchus keta) below Bonneville Dam migrate through as well as hold and spawn in both tributaries and mainstem areas of the Columbia River, USA. Whether fluctuations in tailwater elevation influence spawning in tributaries is unclear. We examined the relationship between Bonneville Dam tailwater elevation, seasonal precipitation and chum salmon spawning activities in three tributary spawning areas. In these tributaries, we assessed initial date of entry, time required to enter and length of spawning season, as well as the proportion of the total population that spawned in tributaries and the distribution of spawners among tributaries. Using linear regression, these variables were compared to cumulative hours of tailwater elevation ≥ 3.5 m and cumulative precipitation. Increased Bonneville Dam tailwater elevation was associated with later and longer lasting chum salmon spawning activities, but was not associated with the distribution of chum salmon spawners in tributaries. Increased seasonal precipitation was associated with a more prolonged spawning season and relatively even distribution of adult chum salmon, but was unrelated to the timing of chum salmon spawning in tributaries. The regulation of tailwater elevation downstream from Bonneville Dam can influence the spawning process for chum salmon in tributaries that enter the regulated area. How important this influence is to the decline of chum salmon in the Columbia River is unclear. Published in 2011 by John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article discusses a histological classification of the maturation stages of the gonads of the fish Leptobotia elongata in order to explore its spawning activity. It also estimates size at maturity to clarify the structures of the reproductive system and to analyze the yearly reproductive cycle of this fish. Five-dependent stages in ovarian maturation were characterized based on the appearance and color of the ovaries and the gonadosomatic index (GSI). Results show that lipid, protein and glycoprotein content varied with the development of the oocytes. Females captured during periods of ovarian ripening had the highest GSI values. The seasonal variation of GSI suggests that the spawning season of L. elongate was from May to July.

This study investigates the vulnerable period in postspawning Pacific oysters ( Crassostrea gigas) through physiological and immunological assessments. After spawning, the oyster condition index reduced by 50% and required 70 days to recover to the prespawning level. The mantle glycogen reduced quickly while the reduction in tissue protein occurred slowly. The mantle tissue also lost more protein than gills. The analysis of adenylate energy charge indicated that oysters were stressed in the first 8 days after spawning. As a result of spawning, haemocyte phagocytosis was reduced and remained at a low level for 3 days. In contrast, the reduction of haemolymph antimicrobial activity did not occur until 3 days after spawning and continued to decline until day 8. This immunesuppression was not directly correlated to the changes in haemocyte density. Our study suggests that the first 8 days after spawning are a critical period for oyster survival due to the loss of energy and low immunity. This study further improves our understanding of the coincidence between spawning and summer mortality in oyster aquaculture. [ABSTRACT FROM AUTHOR]

Regional and interannual variations in spawning activity of Pacific saury Cololabis saira during the northward migration in spring were investigated for 1995-1997 in the north-western Pacific. Only females with a large body size (≥270-290 mm knob length) appeared to spawn. Almost all females in this cohort were actively spawning in a region of sea surface temperature ( TSS) >18° C, the proportion of active spawners appeared positively related to TSS in a region of 13° C < TSS ≤ 18° C, and no females were spawning in the region of TSS ≤13° C. Although this relationship between spawning activity and TSS was common in all years, the distribution of females in the large-size cohort among the regions varied interannually. Consequently, the proportion of active spawners among adult females showed considerable interannual variations. [ABSTRACT FROM AUTHOR]