Long term changes in body condition and gillnet selectivity in Lake Constance pelagic spawning whitefish Coregonus wartmanni

The body condition of Lake Constance pelagic spawning whitefish Coregonus wartmanii has changed substantially during the past century and significantly altered the length-based selectivity of gillnets. Linked hierarchical models using Bayesian inference and error propagation were used to estimate the monthly body condition of whitefish from 1932-2018 and condition-dependent gillnet selectivity from 1964-2018. As expected, body condition followed past trends in nutrient dynamics and was highest in summer months. Body condition was clearly linked to gillnet selectivity, with a weight increase of a 300 mm whitefish from 205 to 260 g predicted to reduce the mean (from 374 to 330 mm) and standard deviation (from 30.8 to 25.1) of lengths selected by a 38 mm mesh gillnet. Simulations demonstrate that such changes can reduce the mean age in harvest by over 1 year and greatly bias population age distribution estimates if selectivity changes are ignored. Similar variation in gillnet selectivity is expected where trophic conditions or other factors cause body condition differences, and accounting for these changes could reduce biases to inform fishery management.

Effects of high pCO2 on early life development of pelagic spawning marine fish

The present study investigated the effect of elevated pCO2 on the development of early stages of the pelagic spawning marine fish Solea senegalensis, Diplodus sargus and Argyrosomus regius. Eggs and larvae were reared under control (pH 8.0, ~570μatm) and two elevated pCO2 conditions (pH 7.8, ~1100μatm; pH 7.6, ~1900μatm) until mouth opening (3 days post-hatching). Egg size did not change with exposure to elevated pCO2, but hatching rate was significantly reduced under high pCO2 for all three species. Survival rate was not affected by exposure to increased pCO2, but growth rate was differently affected across species, with A. regius growing faster in the mid-level pCO2 treatment compared with control conditions. S. senegalensis and A. regius hatched with smaller yolk sacs under increased pCO2 but endogenous reserves of D. sargus were not affected. Otoliths were consistently larger under elevated pCO2 conditions for all the three species. Differences among egg batches and a significant interaction between batch and pCO2 suggest that other factors, such as egg quality, can influence the response to increased pCO2. Overall, the results support the occurrence of a species-specific response to pCO2, but highlight the need for cautious analysis of potential sensitivity of species from unreplicated observations.

Production of Nonadhesive Eggs by Flathead Chub and Implications for Downstream Transport and Conservation

Plains stream fishes in North America, including flathead chub Platygobio gracilis, are negatively affected by stream-flow alterations and fragmentation, and limited information on egg type and reproductive strategy hinders their conservation. On the basis of several lines of evidence, including laboratory culture, observations of reproduction in captivity, and capture and rearing of eggs from Fountain Creek, Colorado, we report that flathead chub produce nonadhesive eggs. Flathead chub eggs are relatively small at 2.3 mm mean diameter, have a greater yolk-to-egg volume ratio and thus sink faster, and take longer to hatch, compared with nonadhesive eggs from pelagic spawning species. Flathead chub are also longer lived compared with pelagic spawning species and the wider variety of habitat types they occupy may influence upstream egg retention. Although spawning mode (e.g., pelagic, lithopelagic, other) is incompletely known for flathead chub, habitat needs in terms of flows and reach lengths suitable for reproduction and recruitment may vary with habitat type but may be similar to that for other pelagic spawning species. Accommodating specialized reproductive life histories of fishes, including egg type and transport characteristics, in stream conservation planning may assist with maintaining or enhancing populations of all Great Plains cyprinids, including increasingly rare flathead chub.

Female belly colour and bobbing behaviour advertise sexual receptivity in a pelagic-spawning coral reef fish

Female nuptial signals (FNSs) advertise reproductive state, individual quality, and are used in intrasexual competition. I explored whether pelagic-spawning pink-belly wrasse (Halichoeres margaritaceus) used red belly colouration and a unique bobbing behaviour as FNSs to advertise spawning readiness. I examined (i) if there was a temporal pattern in belly colour and incidence of bobbing, as each related to spawning; (ii) response of female belly colouration during male courtship behaviours; and (iii) pink belly area as it related to body area and bobbing rate. Temporal patterns were detected, females displayed ephemeral red belly colour and bobbing behaviour prior to spawning; females displaying red belly colouration elicited more courtship behaviour from males than females with white or pink belly colouration, and larger females displayed larger red belly areas. Benefits to advertising spawning readiness in pink-belly wrasse are discussed, including a reduction in mate-searching costs and potential for increased reproductive success through sex-change.

Spawning ascent durations of pelagic spawning reef fishes

Predation risks have been hypothesized to influence spawning behaviors of coral reef fishes that broadcast gametes pelagically. The duration of spawning ascents of 13 species were measured from video footage at a single spawning site for multiple coral reef fishes to investigate if this behavior was influenced by varying risks of predation. Fishes that spawned in pairs had ascents of longer duration than group-spawning species. Duration of spawning ascents did not vary between fishes spawning at daytime and dusk, nor between group-spawning species with specific anti-predatory morphological adaptations. These results indicate that risk of predation may not significantly influence the duration of spawning ascents of pair spawning reef fishes at our study site, while group-spawning behaviors are influenced by predation. Avoidance of egg predation by benthic organisms and female mate choice are more likely to influence the pelagic spawning behaviors of all fishes observed.