Fecundity and Gonadosomatic Index of Sucker Throat Catfish, Pseudecheneis sulcata (McClelland, 1842) from the Snow-fed Tamor River in Eastern Nepal

In comparison to other nations, the Nepalese information on the reproductive biology of hill-stream fish is limited. So, the purpose of the present study was to provide information related to reproductive biology of a hill-stream sucker throat catfish Pseudecheneis sulcata from the snow-fed Tamor River, Nepal. The study was carried out from June 2018 to May 2019. A total of 57 female fish was collected. The fecundity of 22 females was assessed, while the gonadosomatic index was determined using all the collected samples. The absolute fecundity ranged from 2,316 to 7,597 eggs, with an average of 3,660 ± 210. This range of absolute fecundity indicates that Pseudecheneis sulcata is a moderately fecund fish when compared to certain low fecund species and some exceptionally fecund fish with tens of thousands of eggs. Relative fecundity ranged from 65.47 to 129.11 with a mean of 88.98 ± 4.35. The present study demonstrated that absolute fecundity was moderately correlated with total length (r = 0.45) and strongly linked with body weight (r = 0.78), and ovary weight (r = 0.80). Mean gonadosomatic index (GSI) was recorded the highest in January (15.7 ± 1.22%), and showed a decrease in the subsequent month of February (10.3 ± 0.75%), March (6.25 ± 0.28%) and April (1.66 ± 0.40%). The trends of GSI might have indicated that the sucker throat catfish was a batch spawner, with spawning season occuring between January and March.

Mackerel (Scomber australasicus) Reproduction in Northeastern Taiwan

Blue mackerel (Scomber australasicus) is a crucial target species for coastal fisheries in Taiwan, and additionally it has maintained its status as the highest-produced species. The timely measurement of spawning status is crucial for determining the correct management strategy for this species. The objective of this study was to determine size at maturity, fecundity, batch fecundity, and spawning frequency on the basis of samples collected from Nan-Fang-Ao fishing port in Yilan, during the spawning season from 2017 to 2019. Histological sections indicated that the blue mackerel were multiple spawners; a higher percentage of female fish spawned at the peak of the gonadosomatic index. The 50% sizes at maturity were 32.02, 32.13, and 29.64 cm. Mean total fecundity (batch fecundity) was 165 (103), 229 (96), and 210 (68) oocytes per ovary-free weight (g) for 2017, 2018, and 2019, respectively; fecundity was determined through observation of postovulatory follicles (POFs). The spawning frequencies (spawning fraction) in 2017, 2018, and 2019 were 3–10 days (0.13), 4–14 days (0.08), and 4–12 days (0.09), respectively. The spawning frequencies determined through the three estimated methods, namely the sums of (a) hydrated and Day 0 POFs; (b) Day 1+ POFs, and (c) all data combined, were 1 spawning event per 8, 10, and 9 days, respectively. The reproduction of the blue mackerel was greater in 2017 than it was in 2018 or 2019, as indicated by the higher batch fecundity and shorter spawning seasons. Environmental factors should also be considered as a major factor influencing successful reproduction and spawning season

Three rivers and a fish: body shape variation in adult inanga (Galaxias maculatus) and implications for reproductive output

<p>Inanga (Galaxias maculatus) are the major component of New Zealand’s whitebait fisheries. Monitoring of freshwater-based adult populations in both North and South Island river systems suggests a general decline in numbers of fish, and specific streams and watersheds are of particular concern for some regional councils. Given this context, improved information about the environmental conditions that influence inanga’s reproductive output may help to inform appropriate management actions and improve the long term viability of these populations. The breeding biology of adult inanga has been the focus of considerable research effort, with restoration of spawning grounds further extending our knowledge of spatio-temporal patterns of spawning. However, the behaviour patterns and fates of adult fish outside of the spawning locations and seasons are poorly known, as are the factors that may influence the survival and development of pre-spawning stages of inanga. Variation in body shape and size influences multiple performance and fitness attributes, and has major implications for reproduction. My thesis aims to quantify relationships between morphology and reproductive output for adult inanga, and to investigate environmental factors that may influence morphological development. I collected inanga at two discrete stages of adult development: (i) pre-spawning stage adults at upstream habitats and (ii) spawning-stage adults collected at known breeding grounds during the spawning season. I photographed inanga in the field using a purpose-built aquarium and measured a set of morphological characteristics related to reproductive output and swimming ability. Specifically, I measured standard length, head depth, body depth and caudal peduncle depth. A subsample of adult inanga collected during the spawning season were returned to the laboratory and euthanized to measure aspects of their reproductive biology. Specifically, I measured reproductive output using gonad weight, I estimated maturity using the gonadosomatic index (GSI: weight of the gonad relative to total body weight), and I estimated energetic reserves using the hepatosomatic index (HSI: weight of the liver relative to total body weight). Pre-spawning stage inanga in the Waiwhetu Stream displayed deeper bodies than fish in either the Hutt or Wainuiomata Rivers, potentially due to higher concentrations of food. Inanga in the Wainuiomata River displayed slightly larger sizes prior to the spawning season and substantially larger bodies during the spawning season. Although the Waiwhetu Stream may have had a greater supply of food, high densities of fish in smaller stream systems could constrain adult growth. Spawning-stage adults collected from the Waiwhetu Stream had greater reproductive output than fish collected from the Hutt River, with a peak in spawning activity during May. Fish collected from spawning grounds in the Hutt River had lower reproductive output and two peaks in spawning activity during March and May. Inanga in the Hutt River also displayed greater within-month variation in the maturity of fish. My results suggest that spawning grounds in larger, more complex river systems (e.g., the Hutt River) may be supplied by inanga from a diverse range of main stem habitats and smaller tributaries further inland. Smaller systems (e.g., the Waiwhetu Stream) may be comprised of a more homogeneous population of inanga, and reproductive output of the system as a whole may be greater, but concentrated over a shorter time period. I hypothesise that the reproductive output from larger river systems may be more resilient to disturbance events (e.g., stock trampling of spawning grounds) because these systems (by virtue of their greater diversity of habitats and phenotypes of fish) may enable multiple opportunities for spawning. I suggest that larger rivers, such as the Hutt River, may be of disproportionate importance (independent of their total reproductive output) for the replenishment of inanga stocks.</p>

Three rivers and a fish: body shape variation in adult inanga (Galaxias maculatus) and implications for reproductive output

<p>Inanga (Galaxias maculatus) are the major component of New Zealand’s whitebait fisheries. Monitoring of freshwater-based adult populations in both North and South Island river systems suggests a general decline in numbers of fish, and specific streams and watersheds are of particular concern for some regional councils. Given this context, improved information about the environmental conditions that influence inanga’s reproductive output may help to inform appropriate management actions and improve the long term viability of these populations. The breeding biology of adult inanga has been the focus of considerable research effort, with restoration of spawning grounds further extending our knowledge of spatio-temporal patterns of spawning. However, the behaviour patterns and fates of adult fish outside of the spawning locations and seasons are poorly known, as are the factors that may influence the survival and development of pre-spawning stages of inanga. Variation in body shape and size influences multiple performance and fitness attributes, and has major implications for reproduction. My thesis aims to quantify relationships between morphology and reproductive output for adult inanga, and to investigate environmental factors that may influence morphological development. I collected inanga at two discrete stages of adult development: (i) pre-spawning stage adults at upstream habitats and (ii) spawning-stage adults collected at known breeding grounds during the spawning season. I photographed inanga in the field using a purpose-built aquarium and measured a set of morphological characteristics related to reproductive output and swimming ability. Specifically, I measured standard length, head depth, body depth and caudal peduncle depth. A subsample of adult inanga collected during the spawning season were returned to the laboratory and euthanized to measure aspects of their reproductive biology. Specifically, I measured reproductive output using gonad weight, I estimated maturity using the gonadosomatic index (GSI: weight of the gonad relative to total body weight), and I estimated energetic reserves using the hepatosomatic index (HSI: weight of the liver relative to total body weight). Pre-spawning stage inanga in the Waiwhetu Stream displayed deeper bodies than fish in either the Hutt or Wainuiomata Rivers, potentially due to higher concentrations of food. Inanga in the Wainuiomata River displayed slightly larger sizes prior to the spawning season and substantially larger bodies during the spawning season. Although the Waiwhetu Stream may have had a greater supply of food, high densities of fish in smaller stream systems could constrain adult growth. Spawning-stage adults collected from the Waiwhetu Stream had greater reproductive output than fish collected from the Hutt River, with a peak in spawning activity during May. Fish collected from spawning grounds in the Hutt River had lower reproductive output and two peaks in spawning activity during March and May. Inanga in the Hutt River also displayed greater within-month variation in the maturity of fish. My results suggest that spawning grounds in larger, more complex river systems (e.g., the Hutt River) may be supplied by inanga from a diverse range of main stem habitats and smaller tributaries further inland. Smaller systems (e.g., the Waiwhetu Stream) may be comprised of a more homogeneous population of inanga, and reproductive output of the system as a whole may be greater, but concentrated over a shorter time period. I hypothesise that the reproductive output from larger river systems may be more resilient to disturbance events (e.g., stock trampling of spawning grounds) because these systems (by virtue of their greater diversity of habitats and phenotypes of fish) may enable multiple opportunities for spawning. I suggest that larger rivers, such as the Hutt River, may be of disproportionate importance (independent of their total reproductive output) for the replenishment of inanga stocks.</p>

Development of a Quantitative PCR Assay for Four Salmon Species Inhabiting the Yangyangnamdae River Using Environmental DNA

A species-specific quantitative PCR (qPCR) assay using environmental DNA (eDNA) is a promising tool for both qualitative and quantitative analyses of target species directly from water samples. Despite its reliability, an eDNA-based qPCR assay pipeline has not yet developed to monitor salmon species inhabiting Korean waters, which have been rapidly decreasing. We designed species-specific primers for four Oncorhynchus species inhabiting the eastern coastal waters along the Korean Peninsula. These include primers for two native species (Oncorhynchus keta and O. masou) and two that were introduced (O. mykiss and O. kisutch). The limit of detection and limit of quantification for the four qPCR assays ranged from 4.11 to 10.38 copies and from 30 to 81 copies, respectively, indicating a high sensitivity and specificity across all four species. Following optimization, the qPCR assays were used for the quantitative analyses of the four Oncorhynchus species in the Yangyangnamdae River during the spawning and non-spawning seasons in the year 2019–2020, one of the main rivers where salmon migrate during the spawning season in Korea. The raw copy numbers in all of the examined samples were normalized by PCR inhibition rates to standardize and compare with other studies. Among the four Oncorhynchus species examined, the eDNA concentration of O. keta increased significantly (63.60-fold, p < 0.0001) during the spawning season (November) compared with that in the non-spawning season (March), suggesting that O. keta is the main salmon species migrating through the Yangyangnamdae River. In contrast, we did not detect any differences in eDNA concentration for the other three Oncorhynchus species between the spawning and non-spawning seasons, indicating that their presence does not alter during the year. Their eDNA concentration is also relatively low compared to O. keta, which suggests that small numbers of these three species are present in the river. Overall, these newly developed qPCR assays represent useful monitoring tools for the management of four salmon species in Korean waters.

Morphohistological studies of the gonads of hybrid polyploid loach cobitis from the Lower Dniester

In the lower Dniester, polyploid females of the hybrid complex Cobitis taenia are a portion spawning species with asynchronous development of germ cells during the entire breeding period. The spawning season in this water basin begins in the second decade of May and ends in July. In the population, in parallel with females, hermaphrodite individuals are also present, in which the ovary zone is functional, and the testis zone is sterile. A decrease in the relative mass of the gonads of subsequent generations was noted, which leads to a consistent decrease in the value of the gonadosomatic index, in females, before the second and third spawning.

Evaluation of By-Pass Fishway Operation for Attraction Efficiency Based on GPS Drifter Field Experiments

The attraction efficiency of a by-pass fishway installed at Gangjeong-Goryeong Weir on the Nakdong River in South Korea was evaluated according to flow rate variation of the main channel. Optimal flow rate that achieved the maximum value of attraction efficiency at the fishway entrance was also determined. The weir can adjust the flow rate of the main channel and the fishway by operating sluice gates. The weighted usable area (WUA) calculated on the basis of habitat suitability criteria (HSC) for target species using River2D (a two-dimensional physical habitat model) was regarded as an indicator of attraction efficiency. The simulated velocity field by River2D was validated by virtue of measured data acquired from GPS drifter field experiments. Additionally, monthly fish monitoring data obtained with a fish trap served as supporting data to confirm the validity of the estimated attraction efficiency. The monitoring results revealed that the fishway attraction efficiency was the highest during the spawning season (from April to June). The target fish used the fishway most frequently in April. However, many other fish species used the fishway in June. Simulation results revealed that the flow rate of the main channel at the weir should be maintained at 190 m3/s in order to most effectively attract the target fish species into the fishway entrance. Managing the optimal flow rate by operating the sluice gate is especially important during the spawning season of the target fish to facilitate upstream and downstream migration.

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.