Elevated Temperatures Shorten the Spawning Period of Silver Carp (Hypophthalmichthys molitrix) in a Large Subtropical River in China

Global warming is influencing the life history traits of fishes globally. However, the impacts of elevated temperature on fish reproduction are diverse in different regions. Previous studies have revealed that the spawning timing of silver carp (Hypophthalmichthys molitrix) in the Pearl River, in China, has changed over the past decade. However, few studies have explored the potential reasons, which are critical for determining fishing-moratorium periods and developing sustainable fisheries. The current study used discharge suitability index (DSI), temperature suitability index (TSI), correlation and time-series analyses to determine (i) the optimal discharge and temperature for silver carp spawning; (ii) relationships among the thermal regime, hydrological parameters, and spawning timing based on an 11-year time-series dataset. Our results indicated that the most suitable discharge and temperature for silver carp spawning were 13,000–15,000 m3/s and 25–26°C, respectively. The start date of spawning fluctuated with a slight tendency to delay, while the spawning peak and end date obviously occurred earlier during the study period. Correlation analyses suggested that the increasing average temperature between January and March likely caused the initial spawning delay. Moreover, elevated temperatures in August and September probably promoted the anticipated end of silver carp spawning. However, increases in discharge did not significantly correlate with the start of spawning but were significantly and positively correlated with the spawning peak. These results indicated that elevated temperatures shorten the spawning period of silver carp in the Pearl River. Moreover, the initial spawning of silver carp seems to be triggered by temperature rather than changes in discharge; flow pulses can probably create more suitable spawning niches for H. molitrix. This study enhances our understanding of the effect of warming on fish reproduction in subtropical regions.

Differential Regulation of Gonadotropins as Revealed by Transcriptomes of Distinct LH and FSH Cells of Fish Pituitary

From mammals to fish, reproduction is driven by luteinizing hormone (LH) and follicle-stimulating hormone (FSH) temporally secreted from the pituitary gland. Teleost fish are an excellent model for addressing the unique regulation and function of each gonadotropin cell since, unlike mammals, they synthesize and secrete LH and FSH from distinct cells. Only very distant vertebrate classes (such as fish and birds) demonstrate the mono-hormonal strategy, suggesting a potential convergent evolution. Cell-specific transcriptome analysis of double-labeled transgenic tilapia expressing GFP and RFP in LH or FSH cells, respectively, yielded genes specifically enriched in each cell type, revealing differences in hormone regulation, receptor expression, cell signaling, and electrical properties. Each cell type expresses a unique GPCR signature that reveals the direct regulation of metabolic and homeostatic hormones. Comparing these novel transcriptomes to that of rat gonadotrophs revealed conserved genes that might specifically contribute to each gonadotropin activity in mammals, suggesting conserved mechanisms controlling the differential regulation of gonadotropins in vertebrates.

REPRODUÇÃO DE PEIXES DE RIACHO: ESTADO DA ARTE, MÉTODOS E PERSPECTIVAS

Stream fish reproduction is still poorly studied in natural environments, especially in the Neotropical region. In this chapter, we recollect some characteristics of fish reproduction and some questions to guide current research, as: Does sexual dimorphism occur in the species? Which is the mode of reproduction? When and where does the species reproduce? Which environmental factors trigger reproductive events? When does the reproductive life begin? Which is the fecundity? Most of these questions can be answered when we have many specimens available, captured at different periods of the year, measured, weighed and dissected following appropriate protocols. Obtained data represent life history traits that allow to categorize the species in reproductive styles related to parental care and to determine their accordance to models of reproductive strategy associated with the predictability of environmental conditions. We highlight some aspects to be considered in current and future field and lab procedures, such as the recognition of sexual dimorphisms, the importance of naturalistic observation and lab procedures. We draw attention to the advances in studies on reproductive modalities in fish groups well represented in streams, such as inseminating characiforms and viviparous cyprinodontiforms. Finally, we highlight gaps, urgencies, and current perspectives for studies on the reproduction of stream fish, with emphasis on the need for basic studies of species biology, on the importance for building theoretical references and for the conservation of stream habitats in all Brazilian biomes.

Benthic invertebrate communities in the water areas of the Volgograd reservoir near the villages Akhmat and Zolotoye as one of the characterization of conditions for commercial fish reproduction in 2020

The main factor affecting the success of the reproduction of limnophilic fish is the level height and duration of the spring flood with uniform heating of the water. However, the efficiency of fish reproduction also depends on other factors, for example, on the development of the food supply for early juveniles. In 2020, in the water area of the Volgograd reservoir near the villages Akhmat and Zolotoye, according to the results of catches of fry net, developed very unfavorable conditions for the reproduction of commercial fish. The values of production indicators (net primary production and the rate of respiration of the plankton community) in 2020 turned out to be minimal. The dynamics of the abundance, and especially the biomass of benthic invertebrate communities, turned out to be very similar for both water areas in 2018 and very different in 2020. In terms of abundance, among benthic invertebrate communities, in the water area near the village Zolotoye in July 2020, was dominated by oligochaetes and chironomids, and oligochaetes in terms of biomass. At the station near the village Akhmat in July was dominated by chironomids in terms of numbers, and oligochaetes in terms of biomass. In August and September, both in terms of abundance and biomass, oligochaetes dominated in both water areas. There is a correlation between the state of production processes and the state of benthic invertebrate communities in the reservoir. However, the efficiency of fish reproduction correlates, first of all, with the level and temperature regimes of the reservoir during the spawning and feeding period. The decrease in the proportion of underyearlings of crucian carp and perch feeding on benthic invertebrate communities in the catch of fry net in 2020 may be due to both an unfavorable level regime and a drop in the feeding capacity of the water areas.

Effects of Sound from Seismic Surveys on Fish Reproduction, the Management Case from Norway

Anthropogenic noise has been recognized as a source of concern since the beginning of the 1940s and is receiving increasingly more attention. While international focus has been on the effects of noise on marine mammals, Norway has managed seismic surveys based on the potential impact on fish stocks and fisheries since the late 1980s. Norway is, therefore, one of very few countries that took fish into account at this early stage. Until 1996, spawning grounds and spawning migration, as well as areas with drifting eggs and larvae were recommended as closed for seismic surveys. Later results showed that the effects of seismic surveys on early fish development stages were negligible at the population level, resulting in the opening of areas with drifting eggs and larvae for seismic surveys. Spawning grounds, as well as concentrated migration towards these, are still closed to seismic surveys, but the refinement of areas and periods have improved over the years. Since 2018, marine mammals have been included in the advice to management. The Norwegian case provides a clear example of evidence-based management. Here, we examine how scientific advancements informed the development of Norwegian management and how management questions were incorporated into new research projects in Norway.