Hydrological Variation and Fish Assemblage Structure in the Middle Wabash River

We assessed the effect of a severe drought in 1999 upon stream morphology and brook trout (Salvelinus fontinalis) populations in seven headwater streams in the Greenbrier and Potomac River watersheds, West Virginia. During the drought, stream discharge was 96% lower than in years of normal precipitation. As a result, habitat availability and quality over all study streams was significantly lower. Riffle area was greatly reduced (?54%) relative to available pool area (?2%). Fine sediment levels (<0.063 mm) significantly increased within spawning substrate (p=0.01). Water temperature and dissolved oxygen were adequate (mean 15.8?°C, >6.0 mg l^?1, respectively) for brook trout survival in all streams during the drought. Brook trout populations were significantly reduced (adult 60%, Young-of-the-year 67%), and individual fish had significantly lower body condition during the drought relative to the post-drought period. Reductions in brook trout density and population condition during, and in the-post drought period, were related to spatially-limited food resources and/or increased fine sediment levels, but not to degraded water quality. Fisheries managers should consider the effect of periodic drought on brook trout populations and consider short-term harvest restrictions to abet recovery after such stochastic events.     

Endocrine events associated with spawning behavior in the sea lamprey (Petromyzon marinus)

Levels of estradiol, progesterone, and testosterone were determined in plasma of sea lamprey (Petromyzon marinus) undergoing certain behaviors associated with spawning in natural and artificial stream environments. Significantly higher levels of estradiol, progesterone, and testosterone were found in males than in females. In the artificial spawning channel, levels of estradiol were significantly higher in females exhibiting resting and swimming behaviors than in fanning, nest building, and spawning behaviors. No significant correlation was found with either progesterone or testosterone levels and the various reproductive behaviors. The data presented are the first experimental evidence that suggest gonadal steroids may be correlated with certain reproductive behaviors in the sea lamprey.     

Abundance of lamprey larvae and physical habitat

Synopsis Southern brook lamprey larvae,Ichthyomyzon gagei, were collected from four creeks in Alabama and Mississippi. Larvae abundance (number m^–2) and length (mm) were measured over a range of sites to quantify some of the physical parameters involved in larval habitat selection. Particle size distribution, hydraulic conductivity, porosity and organic content were the factors analyzed. Abundance of larvae was greatest when particles smaller than 0.15 mm and 1.–2.0 mm in diameter represented at least 40% and 8% dry weight of the substrate, respectively. Abundance of larvae was lowest when the small particles represented less than 10% dry weight of the substrate. A strong inverse relationship was observed between density and length of larvae. All other parameters did not significantly affect lamprey habitat selection. Results of this study may be applicable in directing attempts at aquatic habitat restoration for lamprey in endangered streams.     

Spawning ecology of flannelmouth sucker, Catostomus lattipinnis (Catostomidae), in two small tributaries of the lower Colorado River

We report the first published accounts of spawning behavior and spawning site selection of the flannelmouth sucker in two small tributaries of the lower Colorado River in the Grand Canyon, Arizona. Spawning was observed on 20 March 1992 and from 28 March to 10 April 1993 in the Paria River, and from 16 to 19 March 1993 in Bright Angel Creek. Flannelmouth suckers exhibited promiscuous spawning behavior–individual females were typically paired with two or more males for a given event and sometimes changed partners between events. Multiple egg deposits by different females sometimes occurred at one spawning site. Flannelmouth sucker selected substrates from 16 to 32 mm diameter in both streams. Spawning occurred at depths of 10 to 25 cm in the Paria River and 19 to 41 cm in Bright Angel Creek. Mean column water velocities at spawning locations ranged from 0.15 to 1.0 m sec^-1 in the Paria River and from 0.23 to 0.89 m sec^-1 in Bright Angel Creek. Water temperatures recorded during spawning ranged from 9 to 18° C in the Paria River and 13 to 15° C in Bright Angel Creek. Spawning flannelmouth sucker ascended 9.8 km upstream in the Paria River and 1.25 km in Bright Angel Creek. Spawning females (410–580 mm) were significantly larger than spawning males (385–530 mm) in the Paria River. The mean size of spawning fish in the Paria River was significantly smaller than the entire stock, averaged throughout the study period (380–620 mm). However, fish spawning in 1992–1993 averaged 53 mm larger than fish spawning in the same reach of the Paria River in 1981, indicating a shift in the size structure of this stock.     

Characterization of a Novel Bile Alcohol Sulfate Released by Sexually Mature Male Sea Lamprey (Petromyzon marinus)

A sulphate-conjugated bile alcohol, 3,12-diketo-4,6-petromyzonene-24-sulfate (DKPES), was identified using bioassay-guided fractionation from water conditioned with sexually mature male sea lamprey (Petromyzon marinus). The structure and relative stereochemistry of DKPES was established using spectroscopic data. The electro-olfactogram (EOG) response threshold of DKPES was 10⁻⁷ Molar (M) and that of 3-keto petromyzonol sulfate (3 KPZS; a known component of the male sea lamprey sex pheromone) was 10⁻¹⁰ M. Behavioural studies indicated that DKPES can be detected at low concentrations by attracting sexually mature females to nests when combined with 3 KPZS. Nests baited with a mixture of DKPES and 3 KPZS (ratio 1∶29.8) attracted equal numbers of sexually mature females compared to an adjacent nest baited with 3 KPZS alone. When DKPES and 3 KPZS mixtures were applied at ratios of 2∶29.8 and 10∶29.8, the proportion of sexually mature females that entered baited nests increased to 73% and 70%, respectively. None of the sexually mature females released were attracted to nests baited with DKPES alone. These results indicated that DKPES is a component of the sex pheromone released by sexually mature male sea lamprey, and is the second biologically active compound identified from this pheromone. DKPES represents the first example that a minor component of a vertebrate pheromone can be combined with a major component to elicit critical sexual behaviors. DKPES holds considerable promise for increasing the effectiveness of pheromone-baited trapping as a means of sea lamprey control in the Laurentian Great Lakes.     

Dissolved phosphorus concentrations and sediment interactions in effluent–dominated Ozark streams

Phosphorus (P) loads from point sources have a significant influence on dissolved P concentrations in streams and sediment-water column dynamics. The goal of this study was to quantify dissolved P concentrations and sediment-P interactions in Ozark (USA) headwater streams with high point source P loads. Specifically, the objectives were to: (1) compare soluble reactive P (SRP) upstream and downstream from wastewater treatment plant (WWTP) effluent discharges; (2) examine longitudinal gradients in SRP downstream from WWTPs; (3) evaluate the effect of WTTP P inputs on sediment-water column P equilibrium and sediment exchangeable P. Water and sediment samples were collected, extracted and analyzed from July 2002 through June 2003 at these Ozark streams. Mean SRP concentrations in the select Ozark streams were significantly greater downstream from effluent discharges (0.08–2.10 mg L⁻¹) compared to upstream (0.02–0.12 mg L⁻¹). Effluent discharge from the WWTPs increased equilibrium concentrations between stream sediments and the water column; mean sediment equilibrium P concentration (EPC₀) was between 0.01–0.07 mg L⁻¹ upstream from WWTP and the increase downstream was proportional to that observed in water column SRP. Sediment exchangeable P (EXP) was greater downstream from the effluent discharges (0.3–6.8 mg kg⁻¹) compared to upstream (0.03–1.4 mg kg⁻¹), representing a substantial transient storage of P inputs from WWTPs. Furthermore, P was generally not retained in these stream reaches when dilution was considered using a hydrologic tracer and was released in one stream reach where effluent P concentrations decreased over the study period. Thus, the effect of the WWTPs was profound in these streams increasing water column and sediment-bound P, and also reducing the ability of these stream reaches to retain P. In P-enriched streams, effluent P discharges likely regulate sediment and aqueous phase P equilibrium and sediment bioavailable P, not the sediments.     

Spawning activities and physical characteristics of the spawning ground of Lethenteron reissneri at the headstream of the Himekawa River, central Japan

 The spawning period of the Far Eastern brook lamprey, Lethenteron reissneri, in the headstream of the Himekawa River is estimated to be between mid-March and late May with the peak of spawning activity between early April and early May. The sex ratio (female:male) in 1999 ranged from 1 : 2.5 to 1 : 3.0 (mean 1 : 2.8) and in 2000 from 1 : 0.8 to 1 : 4.0 (mean 1 : 2.4). In >90% of the observations of spawning nests, males outnumbered females. The construction area of spawning nests tended to shift upstream during the spawning period. The nests were constructed at water depths between 5 and 70 cm, water velocity between 10 and 30 cm/s, and on substrate with pebbles of 5–20 mm in diameter. Lethenteron reissneri constructed nests on substrate similar with Petromyzon marinus, but at shallower points and in areas with a slower water velocity. Received: April 2, 2001 / Revised: December 12, 2001 / Accepted: December 27, 2001     

Larval habitat preference of the endemic Hawaiian midge,Telmatogeton torrenticola Terry (Telmatogetoninae)

Telmatogeton torrenticola Terry is a large endemic chironomid (lastinstar >20 mm) commonly found in high gradient Hawaiian streams on smoothrock surfaces with torrential, shallow flow and in the splash zones ofwaterfalls. We have quantified benthic water flow in larval habitat in a 50m segment of Kinihapai Stream, Maui using a thermistor-based microcurrentmeter. Under base flow conditions at sites suitable for larval attachment,depth was measured and bottom water velocity measurements were made 2 mmabove populations. Larval densities ranged from 386.9–1178m^–2, habitat bottom water velocities from 13.4–64.2 cms^–1, and water depths from 1.5–50 cm. Bottom velocitiesof sites with zero larvae ranged from 20.8–21.8 cm s^–1with depths from 50 to >160 cm. Larval densities were greatest inareas with high bottom water velocities and shallow depths. Stepwisemultiple regression analyses showed that density could be confidentlypredicted best by Froude number (r=0.81; p=0.008). In the absence of Froudenumber as a regression term, the best variable to predict larval density wasbottom velocity ratio: relative depth ratio (r=0.75; p=0.019). In addition,the torrential habitat of the larvae was always characterized by aperiphyton community that appeared to be the primary food resource for thelarvae. These data suggest that torrential flows over appropriate substratesare important factors regulating habitat availability for T. torrenticolaand that reduced discharge (e.g. affected by water diversions) couldsignificantly reduce the amount of available habitat for this organism andother flow sensitive stream fauna.     

Diet,feeding rate,and assimilation efficiency of American brook lamprey

We examined foods ingested by American brook lamprey larvae from Minnesota streams during spring and summer seasons. The diet was dominated numerically by diatoms, but organic detritus comprised the bulk (>85%) of ingested materials. The organic contents of ingested foods did not differ among streams or between seasons, averaging approximately 70%. Feeding rates based on gut fullness were highest, but most variable, during spring. Assimilation efficiency of the organic fraction of the diet averaged >65% across streams and seasons. Larval American brook lamprey depend on organic detritus to meet most of their nutritional needs and are very efficient at digesting and assimilating these detrital foods. Survival of American brook lamprey populations may be affected by human activities that alter the production and availability of detritus within streams.     

The influence of groundwater withdrawal and land use changes on brook charr (<Emphasis Type="Italic">Salvelinus fontinalis</Emphasis>) thermal habitat in two coldwater tributaries in Michigan,U.S.A.

Brook charr (Salvelinus fontinalis) is a sentinel fish species which requires clean, cold water habitats. As such, many jurisdictions in the United States where brook charr are present use this species as an indicator of ecosystem health. In Michigan, groundwater-dominated streams are currently being impacted by increased groundwater withdrawal and land use/land cover changes which alter stream temperatures and their flow, and thus have the potential to significantly influence brook charr production and behavior. We quantified the influence of groundwater withdrawal and land use alteration on thermal habitat availability for brook charr using a groundwater modeling tool that estimated changes in baseflow to a stream segment based on changes to the groundwater system due to groundwater withdrawal and changes in rates of recharge related to landscape changes within a watershed. Projected stream temperature changes were calculated using a stream temperature modeling tool and compared to the range of temperature preferenda for brook charr in order to evaluate the potential impact of policy decisions regarding water extraction and land use/cover changes. The models predicted relatively small changes in both stream baseflow and consequently, stream temperature, with increased groundwater withdrawal rates. Land use/land cover alterations which we analyzed were shown to either mitigate or enhance the loss of brook charr thermal habitat as a result of groundwater withdrawal, depending on its relationship to recharge dynamics. This study emphasizes the importance of collaboration between water, land, and fisheries managers to ensure brook charr population viability, productivity, and sustainability in the face of environmental change, increasing water use and development in the watershed.     

The Atlantic salmon in fresh water: spawning,rearing and production

Summary Fluvial salmonids have evolved to use the diversity of habitats in natural streams for different life history stages and at different seasons. Required freshwater habitat of Atlantic salmon can be classified generally as that suitable (i) for spawning, (ii) for feeding during the major growing period, and (iii) for overwintering.Spawning habitat of salmon is usually in rapid water at the tail of pools on the upstream edge of a gravel bar, ideally with depths about 25 cm, in mean water velocities of about 30–45 cm s^-1, with maximum velocities about 2 body lengths s^-1, and with a substrate of irregularly shaped stones of cobble, pebble, and gravel.Underyearling salmon (<7 cm TL) are most common in shallow (<15 cm) pebbly riffles, whereas older and larger parr (>7 cm TL) are usually in riffles deeper than 20 cm with a coarse substrate. Depth preference increases with size. Multiple linear regression models quantifying parr habitat have identified substrate as an important variable, with a positive relationship to an index of coarseness. Negative relationships were found with mean stream width, range of discharge, and overhanging cover. Water chemistry, especially alkalinity, nitrates, and phosphates, are important regulators of production. Although similar variables had importance, coefficients among rivers differed. Interactions occur among variables. Further studies are required to quantify productive capacity of habitat for parr. Results suggest that useful models can be derived and if a river system is mapped, and stratified by habitat, then smolt yield could be predicted and the required egg deposition could be estimated.In winter, young salmon shelter among coarse substrate or move to pools, but continue feeding, with larger parr being more active.Feeding is in general opportunistic. Food consists mainly of insects, taken primarily in the water column, but also from the surface and at the bottom. Young salmon in flowing water are highly territorial but are less so in slow or still waters. In fast water, parr use their large pectoral fins to apply themselves to the substrate, allowing them to occupy this type of habitat with little expenditure of energy. Height above the substrate decreases with water velocity, but increases with temperature and social status. Although riffles are preferred habitat, and are relatively more productive, lentic waters can be occupied where there are few predators or severe competitors and may provide significant smolt yield in some systems. Selective segregation minimizes competition between salmon and brook charr or brown trout, but brook charr and brown trout may have negative effects on underyearling salmon, and on parr in pools, whereas salmon have negative effects on small brook charr and brown trout in riffles and flats. Competition by both interference and exploitation results in interactive segregation when the resource, mainly food, becomes limiting.Limited downstream movement of underyearling salmon may occur during the summer. Older juveniles may make upstream movements, but generally migrate downstream, with most movements in the spring, and a lesser peak of activity in the autumn. Dispersal tends to be mainly downstream, indicating that for full distribution, spawning areas are best located upstream. High densities of yearling parr may have negative effects on growth and survival of underyearlings in some river systems, but apparently not in others, so that future research is required in this regard. Density-dependent growth is evident where food is limiting, and can provide an indicator of densities of cohorts so that if a quantitative relationship has been derived, mean size from a sample can give an estimate of the density at that station, with minimum size occurring at carrying capacity. Such regressions vary between habitats with differing productive capabilities, so that future research could provide useful models for assessing productive capacity of a habitat, and optimum densities. Life history strategies can change with changes in density-dependent growth rates. Present stock-recruitment functions do not take environmental variables into consideration, and have limited applicability. Further research is required to determine optimum spawning requirements for salmon in different types of river systems in different geographical areas.     

Predictability of streamflow and particulate organic matter concentration as indicators of stability in prairie streams

Predictability of stream discharge and particulate organic matter (POM) in the water column was estimated, using Colwell's indices of constancy and contingency, for 6 Texas prairie streams (1 each of 2nd, 3rd, and 4th order with intermittent or perennial discharge). Stream discharge in these 6 prairie streams varied between 0 and 36000 1 s^–1, depending on the stream and season. Predictability (P) of discharge in these streams ranged from 0.45 to 0.62, within the range of values expected for North American streams. Predictability of stream discharge was not significantly different between streams. Particulate organic matter concentrations in these prairie streams are relatively low, ranging from 0.25 to 4.00 mg AFDM 1^–1. Predictability of POM concentration in these streams was high, ranging from 0.75 to 0.85, and was largely the result of constancy of POM concentrations. Within the different POM size classes, Fine POM (FPOM) had the highest predictability (P = 0.89–0.96). In spite of relatively unpredictable stream discharge, POM remained fairly constant providing a measure of habitat predictability and stability.     

Individual and group characteristics affecting nest building in sea lamprey (Petromyzon marinus L. 1758)

Nest building relates to reproductive effort, sexual selection, intersexual conflict and cooperation and may be linked to individual phenotype and interindividual interactions. In particular, larger individuals having more energy reserves are expected to build more, larger nests, without having to trade intrasexual competition for cooperative nest building. Capture–mark–recapture and nest survey of sea lamprey (Petromyzon marinus L. 1758) were combined to assess the relationship between individuals and nesting activity on a spawning ground, throughout a breeding season, during which 202 nests were observed and 114 individuals were captured. On average, males and females stayed 8.33 ± 1.02 and 3.57 ± 1.04 days on the spawning ground, visited 2.26 ± 1.72 and 1.67 ± 1.17 nests and encountered 2.33 ± 2.13 mates for males and 2.29 ± 1.32 mates for females, respectively, and the number of mates encountered increased with the number of nests visited. Body size had no effect on the duration of presence on spawning ground, number of nests visited, number of individuals per nest and sex ratio on nest or nest volume. Bigger nests were found at the end of the season and were not necessarily built by more individuals. This work brings insights on the mating system and cooperative nest building in sea lamprey and may inform managers who want to estimate sea lamprey populations via nest surveys.     

Longitudinal and seasonal pattern of insect emergence in alpine streams

Prevailing water sources and/or regional climate are known to have an important influence on hydromorphology and chemistry of high alpine streams, affecting biology and phenology of aquatic insects considerably. Seven reaches in two different stream types (glacial and non-glacial) in the European Central Alps were investigated along a longitudinal gradient above the tree line to elucidate community structure and emergence patterns of aquatic insects. Aquatic insect emergence was dominated by chironomid taxa in both streams (95.0% in the glacial vs. 90.5% in the spring-fed stream). Emergence rate was much higher in the non-glacial stream, with Chironomidae 638.9 ind. m⁻² d⁻¹ and EPT (Ephemeroptera, Plecoptera, Trichoptera) 20.3 ind. m⁻² d⁻¹ (annual mean), compared to the glacial stream (Chironomidae 132 ind. m⁻² d⁻¹ and EPT 7.0 ind. m⁻² d⁻¹). Whereas, in the glacial stream a richer and more diverse species composition was found at lower elevations, emergence rate and emerging taxa numbers were higher at higher altitude in the non-glacial stream. Seasonal comparisons also showed a significant difference between the two streams. In the glacial stream maximum emergence was in April/May, whereas, in the non-glacial stream in July. A comparison with similar studies carried out in alpine streams showed that abundance and biomass of emerging insects were relatively low in the glacial stream. The continuous emergence throughout the summer is another example of insect life-cycle adaptation to the harsh environmental conditions in glacial streams: most likely, emergence during the warmer summer months, where the probability of experiencing favourable climate conditions on land is higher than for the rest of the year, was an evolutionary advantage for many glacial stream taxa.     

Interspecific territoriality in males of the tube blenny <Emphasis Type="Italic">Neoclinus bryope</Emphasis> (Actinopterygii: Chaenopsidae)

Territoriality was investigated in the tube blenny Neoclinus bryope (Actinopterygii: Chaenopsidae) at rocky intertidal areas of Banda Beach, Tateyama Bay, central Japan. Males used small holes as spawning nests, usually staying at the nest and maintaining the area while showing exclusive behaviors. Their home ranges were limited to areas within 30 cm distance from the nest for over 2 months. Four heterospecific fishes were threatened when they approached to within 6–14 cm of the nest holes, and two species of carnivorous snails were removed at points 0–30 cm from the nest entrance. There were no significant differences between the distances from the nest entrances to the points defended against fish and those used for foraging. As the four heterospecific species have similar feeding habits to those of N. bryope, the area defended against fishes may function as a foraging territory. At 24 h following the removal of nest owners, carnivorous snails had gathered to actively prey on eggs, indicating that the area defended against snails may function as a territory for protection against egg predators. Although the positions of females where males started courtship displays were significantly farther than the foraging points and the positions of threatened fishes, males displayed no territoriality against conspecific males. The fact that males did not leave the nest hole during the courtship suggests that it may be costly to maintain a courtship territory. These results show that males of tube blenny maintain territories for egg guarding and for protecting food resources around their nest holes in the spawning season.     

Effects of Large Woody Debris Addition on Stream Habitat and Brook Trout Populations in Appalachian Streams

Large woody debris (LWD) was added to eight streams in the central Appalachians of West Virginia to determine if stream habitat could be enhanced and brook trout (Salvelinus fontinalis) populations increased. Brook trout populations were assessed one year prior to habitat manipulation and 3 years post-habitat manipulation. LWD was added by felling approximately 15 trees per 300 m stream reach. Four of the streams had LWD added to one 300 m reach with 300 m unmanipulated reaches upstream and downstream of the manipulated reach to observe within-stream effects of LWD additions on brook trout density. The remaining four streams had LWD added to three 300 m reaches and these streams were compared to those with only a single 300 m manipulated reach to observe the effects of the extent of habitat manipulation on brook trout density. New pools were formed by the addition of LWD, but overall pool area did not increase significantly in reaches where LWD was added. The relatively high gradient and coarse substrate of these streams may have precluded the added LWD from having a significant influence on stream channel morphology and habitat complexity. No pools were formed in the highest gradient stream, while the stream with the most pools formed had the lowest gradient. Brook trout populations fluctuated following habitat manipulations, and there was no overall effect of the LWD additions on within-stream variability in brook trout density. When there were significant differences among-streams with different extents of LWD additions, those streams receiving LWD additions over a large extent had the greatest brook trout densities. The full potential of added LWD to change stream habitat and influence on brook trout populations may take more time to develop than the 3 years post-manipulation period of this study.     

Comparison of brook trout reproductive success and recruitment in an acidic adirondack lake following whole lake liming and watershed liming

Limestone applications to the catchment of one tributary to Woods Lake were highly effective in reducing stream acidity and stabilizing seasonal fluctuations in pH. The resulting improvement in stream water quality also led to a dramatic shift in reproductive strategy of the Woods Lake brook trout population. Prior to catchment liming, brook trout in Woods Lake were restricted to spawning on poor quality near shore substrate with limited ground water seepage. Reproductive success was limited by high mortality of eggs and larvae and recruitment from in lake spawning was not successful. Spawning brook trout did not utilize the tributary for spawning prior to watershed liming. Mitigation of acidity in the tributary, by catchment liming, effectively extended the spawning habitat available to the Woods Lake brook trout population and one year following treatment brook trout spawned successfully in the tributary for the first time in 6 years of observation. Significant recruitment of young trout into the lake population occurred from 1991 through 1993, although the absolute number of fish captured was relatively small. In the fall of 1993, four year classes of naturally spawned brook trout were present in the lake. Although reproductive success was enhanced by improving tributary spawning habitat in the Woods Lake basin, self maintenance of the population may be limited by low recruitment rates of young trout, due to high levels of summer mortality resulting from predation. Mitigation of this constraint would require substantially higher levels of fry production than were observed in Woods Lake and/or enhanced refugia for young trout. The results of this experiment suggest that re-establishment of tributary spawning populations of brook trout may be possible, with future reductions in acidic deposition, in acidic Adirondack lakes with limited in-lake spawning habitat.     

Age,growth, and sex ratio among populations of least brook lamprey,Lampetra aepyptera,larvae: an argument for environmental sex determination

Synopsis Sex ratios of least brook lamprey,Lampetra aepyptera, larvae varied widely among 12 geographically-diverse streams of the eastern United States. The extremes were 29 and 71% male, and the proportion of males increased significantly with relative population density, which was estimated among the streams from the number of larvae collected per m2 of substrate. The skewed sex ratios were not likely due to differential mortality between the sexes or differential recruitment to the adult stock, since they were established at the time of gonadal differentiation (at ca. 2 years of age) and remained relatively constant over the subsequent 2–3 years of larval life. Furthermore, although females seemed to predominate in the oldest larval age class, thus appearing to metamorphose later than males, their numbers were small and were omitted from the overall sex ratio. Sex ratio did not vary significantly with water hardness, pH, annual thermal units, or latitude. The possible adaptive significance of density-dependent sex determination in lampreys, however, remains elusive. It has been proposed that growth-promoting conditions might yield female-biased sex ratios as a tactic for ensuring that relatively large individuals become females, thereby increasing their fecundity. As predicted, larval size at a given age was generally greater in low-density populations, but there was no relationship between sex ratio and larval size, and female larvae were not consistently larger than the males.     

Simultaneous spawning by female stream goby Rhinogobius sp. and the association with brood cannibalism by nesting males

A laboratory experiment was conducted by varying the undersurface area of nesting substratum and the number of females in an experimental tank to elucidate the determinants of the mating pattern in the stream goby, Rhinogobius sp. cross‐band type. Males with larger nests tended to attract two or more females to their nest in a tank. Moreover, males spawned simultaneously with multiple females and entire brood cannibalism by males was rarely observed under a female‐biased sex ratio. When males spawned with a single female with low fecundity, however, entire brood cannibalism occurred at a high frequency, suggesting that a male guarding a nest with fewer eggs consumes the brood. Therefore, spawning behaviour of females that leads to a large egg mass would decrease the risk of entire brood cannibalism. In this species, simultaneous spawning by multiple females in a nest serves as a female counter‐measure against entire brood cannibalism. These results suggest that a conflict of interest between the sexes through brood cannibalism is a major determinant of simultaneous spawning.     

High frequency of mating without egg release in highly promiscuous nonparasitic lamprey <Emphasis Type="Italic">Lethenteron kessleri</Emphasis>

Nonparasitic lampreys are highly promiscuous: a single female can mate over several dozen times with multiple males. It remains unknown why females mate so frequently despite presumed costs from an elongated spawning period. This paper documents that female Siberian brook lampreys mate without egg release (termed “sham mating”) at remarkably high frequencies. Females mated 20–196 times during a breeding experiment, of which sham mating comprised 35–90%. The number of eggs released may be physically constrained in each mating by the lamprey’s elongated body and behavior. Female lampreys might also control egg release depending on surrounding males.