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>

Ichthyoplankton DNA metabarcoding: challenges and perspectives

DNA metabarcoding has been widely used to access and monitor species. However, several challenges remain open for its mainstream application in ecological studies, particularly when dealing with a quantitative approach. In a from the Cover article in this issue of Molecular Ecology, Cédric et al. (2021) report species-level ichthyoplankton dynamics for 97 fish species from two Amazon river basins using a clever quantitative metabarcoding approach employing a probe capture method. They clearly show that most species spawned during the rainy season when the floods started, but interestingly, species from the same genus reproduced in distinct periods (i.e., inverse phenology). Opportunistically, Cédric et al. (2021) reported that during an intense hydrological anomaly, several species had a sharp reduction in spawning activity, demonstrating a quick response to environmental cues. This is an interesting result since the speed at which fish species can react to environmental changes, during the spawning period, is largely unknown. Thus, this study brings remarkable insights into basic life history information that is imperative for proposing strategies that could lead to a realistic framework for sustainable fisheries management practices and conservation, fundamental for an under-studied and threatened realm, such as the Amazon River basin.

Diel Patterns of Pheromone Release By Male Sea Lamprey

Costs to producing sexual signals can create selective pressures on males to invest signaling effort in particular contexts. When the benefits of signaling vary consistently across time, males can optimize signal investment to specific temporal contexts using biological rhythms. Sea lamprey, Petromyzon marinus, have a semelparous life history, are primarily nocturnal, and rely on pheromone communication for reproduction; however, whether male investment in pheromone transport and release matches increases in spawning activity remains unknown. By measuring 1) 3keto-petromyzonol sulfate (3kPZS, a main pheromone component) and its biosynthetic precursor petromyzonol sulfate (PZS) in holding water and tissue samples at 6 points over the course of 24 hours, and 2) 3kPZS release over the course of several days, we demonstrate that 3kPZS release exhibits a consistent diel pattern across several days with elevated pheromone release just prior to sunset and at night. Trends in hepatic concentrations and circulatory transport of PZS and 3kPZS were consistent with patterns of 3kPZS release and suggest the possibility of direct upregulation in pheromone transport and release rather than observed release patterns being solely a byproduct of increased behavioral activity. Our results suggest males evolved a signaling strategy that synchronizes elevated pheromone release with nocturnal increases in sea lamprey behavior. This may be imperative to ensure that male signaling effort is not wasted in a species having a single, reproductive event.

Reproductive traits and spawning activity of striped eel catfish (Plotosidae) in Kolono Bay, Indonesia

Asriyana A, Halili H. 2021. Reproductive traits and spawning activity of striped eel catfish (Plotosidae) in Kolono Bay, Indonesia. Biodiversitas 22: 3020-3028. Reproduction is a natural process for a species to ensure its sustainability in nature. This study aimed to investigate the reproductive traits and spawning activity of the striped eel catfish in Kolono Bay, South Konawe District, Southeast Sulawesi, Indonesia. A total of 965 individuals were collected monthly from June 2020 to May 2021 by using bottom experimental gillnets. Spent/spawning stages of the male and female fish were found during the East season (June-August). The proportions of the spent/spawning stages of male and female fish were 60% and 55.56% and the values of the gonadal somatic index were 1.19 ± 0.53 and 2.19 ± 3.47, respectively during the East season, indicate occurring the peak spawning in this season. Females matured gonads more rapidly at 198.3 mm compared to males at 224.5 mm. Female fecundity was 1,730 ± 390 eggs, with an egg diameter of about 0.11-1.35 mm. Striped eel catfish is a total spawner fish that has one mode of egg distribution pattern. During the East season, it needs protection for spawning. The findings will help in designing effective management and developmental strategies to conserve the striped eel catfish population in the future.

Reproductive traits in dolphinfish Coryphaena hippurus Linnaeus, 1758 along the coastal waters of Karnataka, south-eastern Arabian Sea

The maturity, sex ratio, gonadosomatic index (GSI) and fecundity of Coryphaena hippurus was investigated from 347 specimens collected along Karnataka coast, south-eastern Arabian Sea from August 2017 to May 2018. Overall sex ratio of 1:3.5 (male:female) indicated dominance of females in the fishery and differed significantly (p<0.05) in all the months, except in January, May and December. The fork length (FL) at 50% maturity (Lm50) was estimated at 47.5 cm for both males and females. The pattern of GSI and maturity stages suggests peak spawning activity in August-September. However, the incidence of fishes capable spawning all through the year in varied proportions implied that spawning activity occurs throughout the year. The absolute fecundity estimates varied from 1,00,298 eggs for a female of 53.5 cm FL to 6,15,267 eggs for female of 113 cm FL with an average fecundity of 3,18,446 eggs per female. Thefecundity of fish increased with body length and weight as well as with gonad weight. The biological information on maturation, reproductive cycle, spawning periodicity and fecundity of C. hippurus in the tropical Arabian Sea could be useful for developing appropriate management tools and conservation strategies for this commercially important fish species.

A quantitative eDNA-based method to monitor spawning activity of two emblematic fish species in lake Geneva

Anthropogenic pressures and more recently climatic change have increased the interest to study the impact of environmental changes on the key stages of fish life cycle. In lake Geneva, a deep peri-alpine lake, climate change and phosphorous level are known to have consequences on salmonid and percid populations, including key species for recreational and commercial fisheries, whose stocks are subject to significant fluctuations. To follow these stock variations, the spawning activity of European perch (Perca fluviatilis) and whitefish (Coregonus lavaretus) is monitored in this lake since several years using traditional methods, unfortunately mostly destructive or damaging (e.g. gillnetting and collection of fertilized eggs). DNA isolated from the environment (eDNA) has been widely developed for the detection of specific species or whole biological communities, and this non-invasive method offers an alternative to conventional surveying tools. Until recently, the methods used for eDNA analysis (e.g. qPCR, metabarcoding) could be limited by their sensitivity, quantification limit or price, but the emergence of new methods, such as the droplet digital PCR (ddPCR), offers the possibility to quantify an absolute eDNA signal in a very sensitive way and at a lower cost. Here, we show for the first time the applicability of an eDNA method to monitor the spawning activity of two fish species in a lake by using ddPCR. During two spawning seasons for whitefish and one spawning season for European perch, water samples were collected every week from the subsurface, simultaneously to traditional monitoring sampling, and filtered through sterile cartridges. The eDNA was then extracted and analyzed using ddPCR, targeting the mitochondrial DNA of the two fish species. The results demonstrate the efficiency of eDNA coupled with ddPCR to identify the timing and duration of the spawning periods, as well as the peak of the spawning activity for whitefish and European perch in Lake Geneva. This study shows that we have reached an operational level to use this non-invasive eDNA monitoring of the spawning activity of these fish species in lakes.

Reproductive biology of the rayed pearl oyster (Pinctada imbricata radiata, Leach 1814) in Izmir Bay

The present study was carried out to determine gonadal stages and quality of pearl oyster meat (Pinctada imbricata radiata, Leach, 1814) in Izmir Bay (Turkey). Pearl oyster samples were collected from the study area at a depth of ~5 m between February 2013 and January 2014. The highest and lowest temperature was measured in July and January as 27°C and 14.2°C, respectively. The maximum chlorophyll a value of 4.640 μg l−1 was calculated in May and the lowest value of 1.009 μg l−1 was recorded in April. Individuals reached their first maturity in April. Spawning activity was observed from June to September and the gonad index (GI) was at the highest level during those months. The development was observed from April to February. The overall female to male ratio was 1.32:1 (p < 0.05) and it did not affect the GI (p > 0.05). There is a strong positive correlation between the GI and temperature (p < 0.05). The highest condition index (CI) was recorded in May as 12.31 ± 0.51, whereas the lowest one in January as 7.37 ± 0.22. As a result, this study revealed that the pearl oyster population in the region is characterized by high reproductive activity, especially during the summer months.