Egg Size In Fishes Research Articles

Effects of diameter, density, and adhesiveness on settling velocity and drag coefficient of two sturgeon species eggs in flow

Motion of eggs has received increasing attention because they are different from inanimate particles in physical and biological properties (density, diameter and adhesiveness), which determines their motion mechanism. Settling and drifting experiments were conducted to measure and identify the transport mechanism of eggs of two sturgeon species, Siberian sturgeon and Amur sturgeon. The terminal settling velocities are 4.30 ± 0.19 cm s−1 and 4.85 ± 0.22 cm s−1 for adhesive and de-adhered Siberian sturgeon eggs, respectively, and 5.23 ± 0.16 cm s−1 and 5.46 ± 0.19 cm s−1 for adhesive and de-adhered Amur sturgeon eggs, respectively. Adhesiveness decreases the terminal settling velocity. Meanwhile, the terminal settling velocity increases with increasing fish egg size. We developed a formula for the drag coefficient of sturgeon eggs and verified it via drifting experiments. The drag coefficient of sturgeon eggs is mainly affected by adhesive force when the Reynolds number R e ≤ 700 and by inertial force when R e > 700. The results show that sturgeon eggs differ significantly from other solid particles in their behaviour and an exclusive formula is necessary. This further provides new insights into the movement of adhesive demersal eggs and supports numerical simulation of their transportation in natural rivers.

Global environmental drivers of marine fish egg size

AbstractAimTo test long‐standing theory on the role of environmental conditions (both mean and predictability) in shaping global patterns in the egg sizes of marine fishes.LocationGlobal (50° S to 50° N).Time period1880 to 2015.Major taxa studiedMarine fish.MethodsWe compiled the largest geo‐located dataset of marine fish egg size (diameter) to date (n = 1,078 observations; 192 studies; 288 species; 242 localities). We decomposed sea surface temperature (SST) and chlorophyll‐a time series into mean and predictability (seasonality and colour of environmental noise – i.e. how predictable the environment is between consecutive time steps), and used these as predictors of egg size in a Bayesian phylogenetic hierarchical model. We test four specific hypotheses based on the classic discussion by Rass (), as well as contemporary life‐history theory, and the conceptual model of Winemiller and Rose ().ResultsBoth environmental mean and predictability correlated with egg size. Our parsimonious model indicated that egg size decreases by c. 2.0‐fold moving from 1 to 30 °C. Environments that were more seasonal with respect to temperature were associated with larger eggs. Increasing mean chlorophyll‐a, from 0.1 to 1 mg/m3, was associated with a c. 1.3‐fold decrease in egg size. Lower chlorophyll‐a seasonality and reddened noise were also associated with larger egg sizes – aseasonal but more temporally autocorrelated resource regimes favoured larger eggs.Main conclusionsOur findings support results from Rass () and some predictions from Winemiller and Rose (). The effects of environmental means and predictability on marine fish egg size are largely consistent with those observed in marine invertebrates with feeding larvae, suggesting that there are important commonalities in how ectotherm egg size responds to environmental change. Our results further suggest that anthropogenically mediated changes in the environment will have profound effects on the distribution of marine life histories.

Bathymetric gradients of fecundity and egg size in fishes: A Mediterranean case study

There is a general hypothesis that species inhabiting deep-sea waters have lower fecundity and larger eggs than shallower species. However, there are few comparative studies which explore this trend because of the complexity of sampling in deep waters, especially in fishes. We present here the first analysis of fecundity and egg size with depth along an isothermal environment. We calculate the relative fecundity and egg size of 11 species of demersal deep-sea fish from the western Mediterranean and included in our analyses published data for an additional 14 species from the same geographic area. The results show that the relative fecundity (eggs per g of individual) of the analyzed fishes slightly decreased along the bathymetric gradient, whereas egg size increased with depth. When the analysis was conducted including only species from the order Gadiformes, the most speciose group in the region and with the widest depth range of distribution (50–2000m), there was no relationship between relative fecundity and depth, while the deepest species had larger egg sizes than shallower ones. The finding of similar relative fecundities but larger egg sizes suggests that these deep-sea species are investing a higher amount of energy in the production of offspring than shallower water counterparts. The results are discussed in relation to the isothermal characteristics of the deep Mediterranean Sea and ecological adaptations for reproductive success.

The maternal effect of differences in egg size influence metabolic rate and hypoxia induced hatching in Atlantic salmon eggs: implications for respiratory gas exchange across the egg capsule

The maternal effect of fish egg size has profound implications for oxygen transfer across the egg shell surface, and therefore metabolism, especially under adverse environmental conditions like hypoxia. We found that metabolic rate ([Formula: see text]) of Atlantic salmon alevins was higher than of eggs in normoxia and hypoxia. Equally, the [Formula: see text] of smaller eggs from maiden spawners was lower than that of larger eggs from repeat spawners. Critical partial pressure of oxygen (PO2) for hatching was lower in eggs from repeat spawners. Generally, the PO2within the egg capsule was lower for a given ambient PO2and decreased further with hypoxia, and the internal PO2was higher, the bigger the volume of the egg. Therefore, we conclude that the egg capsule poses a major barrier to oxygen exchange for the mature embryo that is more severe in eggs from maiden spawners than in eggs from repeat spawners. This was corroborated by a more advantageous egg surface area to [Formula: see text] ratio in eggs from repeat spawners. These findings challenge the “bigger is worse during incubation” hypothesis.

A phylogenetic analysis of egg size, clutch size, spawning mode, adult body size, and latitude in reef fishes

Theoretical treatments of egg size in fishes suggest that constraints on reproductive output should create trade-offs between the size and number of eggs produced per spawn. For marine reef fishes, the observation of distinct reproductive care strategies (demersal guarding, egg scattering, and pelagic spawning) has additionally prompted speculation that these strategies reflect alternative fitness optima with selection on egg size differing by reproductive mode and perhaps latitude. Here, we aggregate data from 278 reef fish species and test whether clutch size, reproductive care, adult body size, and latitudinal bands (i.e., tropical, subtropical, and temperate) predict egg size, using a statistically unified framework that accounts for phylogenetic correlations among traits. We find no inverse relationship between species egg size and clutch size, but rather that egg size differs by reproductive mode (mean volume for demersal eggs = 1.22 mm3, scattered eggs = 0.18 mm3, pelagic eggs = 0.52 mm3) and that clutch size is strongly correlated with adult body size. Larger eggs were found in temperate species compared with tropical species in both demersal guarders and pelagic spawners, but this difference was not strong when accounting for phylogenetic correlations, suggesting that differences in species composition underlies regional differences in egg size. In summary, demersal guarders are generally small fishes with small clutch sizes that produce large eggs. Pelagic spawners and egg scatterers are variable in adult and clutch size. Although pelagic spawned eggs are variable in size, those of scatterers are consistently small.

Fish egg size: a characteristic determined by parental care

Fish egg size: a characteristic determined by parental care

Juvenile exposure to predator cues induces a larger egg size in fish

When females anticipate a hazardous environment for their offspring, they can increase offspring survival by producing larger young. Early environmental experience determines egg size in different animal taxa. We predicted that a higher perceived predation risk by juveniles would cause an increase in the sizes of eggs that they produce as adults. To test this, we exposed juveniles of the mouthbrooding cichlid Eretmodus cyanostictus in a split-brood experiment either to cues of a natural predator or to a control situation. After maturation, females that had been confronted with predators produced heavier eggs, whereas clutch size itself was not affected by the treatment. This effect cannot be explained by a differential female body size because the predator treatment did not influence growth trajectories. The observed increase of egg mass is likely to be adaptive, as heavier eggs gave rise to larger young and in fish, juvenile predation risk drops sharply with increasing body size. This study provides the first evidence that predator cues perceived by females early in life positively affect egg mass, suggesting that these cues allow her to predict the predation risk for her offspring.

The effect of egg size and nutrient content on larval performance: implications to protracted spawning in northern pike (Esox lucius Linnaeus)

Variation in developmental rate from fertilization to swim-up, and body size at swim-up, may affect the growth and survival of young-of-the-year fish. Fish egg size (diameter) is often positively correlated to adult female size, but whether increased egg size equates to higher egg nutrient content and subsequently improved embryo/larval performance, remains unclear. Artificially fertilized northern pike eggs from individual females (total length 400–800 mm) were cultured under temperature controlled laboratory conditions to test the hypothesis that female body size positively influences egg size and the amount of specific nutrients (carbon, nitrogen, phosphorus, and fatty acids) allocated to eggs. We further hypothesized that greater egg nutrient content would positively influence egg survival, developmental rate, and the size of swim-up fry. These hypotheses were investigated in the context of two different northern pike spawning strategies (early season tributary vs. late season deep shoal spawning). Nutrients were allocated conservatively in northern pike eggs, showing very little variation in nutrient concentrations, but the total mass of all egg nutrients increased linearly with egg dry mass. Neither egg dry mass nor nutrient content (concentration or mass), were related to either egg diameter or female body size. The mass of individual egg nutrients was, however, strongly correlated with egg dry mass (r 2 range 0.62 to 0.99 for individual nutrients) and positively related to the total length of swim-up fry (r 2 = 0.58). The eggs of late spawning pike had significantly greater dry mass (average = 3.02 mg/egg) and developed more rapidly to swim-up (average = 17.89 days) than did those of early spawners (average = 2.28 mg/egg, 19.05 days). Our results indicate that egg quality may be best assessed by egg dry mass, which was correlated with greater nutrient mass and increased swim-up fry body length, as opposed to egg diameter or female body size which showed no correlation to egg nutrient composition and egg/larval performance.

Oxygen as a constraining factor in egg size evolution in salmonids

Differential survival at low oxygen levels has been proposed as a mechanism for maintaining high within-population variability in egg size in fish. Whether low oxygen levels favour large or small eggs, however, is not clear. To address this question, the effects of egg size on metabolic rates, critical dissolved oxygen levels (Pc), and P50oxygen levels of Chinook salmon (Oncorhynchus tshawytscha) embryos and alevins were determined. Embryonic metabolic rate expanded at a slower rate with increasing egg mass (allometric constant (b) = 0.30) than did capsule surface area (b = 0.67), indicating that larger eggs have larger surface areas relative to their metabolic demand for oxygen. A relatively larger area, however, did not translate into significant differences in Pcor P50values at the egg stage. After hatch, metabolic rate expanded at a rate proportional to (egg mass)0.62. Pclevels were significantly higher for alevins from larger eggs for the first but not second half of the alevin stage. Egg size had no significant effect on P50values at any time during the alevin stage. The modest impact of egg size on hypoxic tolerance of developing Chinook suggests that factors other than oxygen are involved in maintaining high within-population variability in egg size.

Automated egg counting and sizing from scanned images: Rapid sample processing and large data volumes for fecundity estimates

The production of eggs in a fish population is a fundamental parameter in fisheries management and ecology. Management decisions are based largely on the abundance and composition of the spawning stock; hence it is essential to estimate the contribution of viable eggs by females of various ages, which may depend on the size and maturation schedules in females of younger ages, and the size and reproductive senescence of older ones. The level of recruitment may also be influenced by the size and quality of eggs. Egg quality can be characterised in a number of ways; however, the most useful methods are those that are efficient and widely available. Estimating potential fecundity and egg size in fish and invertebrate populations has been hindered by the processing time, toxicity, and resources required by traditional methods. We have developed an imaging-based technique that counts and measures oocytes from a gravimetric gonadal sub-sample in relatively little time and at low cost. Sub-samples were preserved in a non-toxic formulation of Gilson's solution, which offers an alternative to other preservatives commonly used in fecundity studies. The technique uses high-resolution optical scans of plated oocytes, imaging software, and user-defined object classifications to separate oocyte from ancillary material likely to be present in a processed sample. Estimates of misclassification are as low as 1% (false-negatives) in automated counts.

Does Within‐Population Variation in Fish Egg Size Reflect Maternal Influences on Optimal Values?

Various models that assume correlations between maternal phenotype and offspring environment predict adaptive variation in egg size within populations. Here we conduct a comparative test of these models using published data on fish egg size. Intrapopulation variation in egg size was most pronounced in fish with demersal eggs and larvae (median coefficient of variation [CV] at family level = 6.5%), where offspring environment is likely influenced by maternal phenotype, and least so in fish with pelagic eggs (CV = 3.6%), which experience a relatively stochastic spatial distribution during incubation. This difference was significant at various taxonomic levels, was robust to variation in mean egg size and habitat (i.e., freshwater or marine), and was mirrored in independent paired contrasts. Fish with demersal eggs and pelagic larvae were not significantly different from those with pelagic eggs (CV = 3.8%), indicating that selection favoring within-population variation in egg size occurs mainly posthatching and that any such selection occurring prehatching may be less intense. These results suggest that patterns of within-population variation in egg size among fish taxa reflect adaptive processes and that maternal effects on the egg size-fitness function may explain apparent discrepancies from the single-optima Smith-Fretwell model.

MATERNAL AND ENVIRONMENTAL GRADIENTS IN THE EGG SIZE OF AN ITEROPAROUS FISH

Life history theory predicts that organisms inhabiting environments with relatively poor conditions for the growth and survival of their offspring should produce fewer and larger offspring. We examined egg size (an index of offspring size) of an iter- oparous, broadcast-spawning, freshwater fish-the walleye (Stizostedion vitreum)-from 34 populations across 260 of latitude in order to determine whether egg size varied with respect to environmental indices of juvenile habitat quality. Variation among populations (among environments) was compared to variation within populations (among females). Within populations, egg size generally increased with maternal size and age. Slopes of these relationships were much more variable among populations (cv > 100%) than inter- annually within populations (cv 10%) than interannually within populations (cv < 5%), but only slightly more variable than among females within populations (mean cv = 8.5%). Nev- ertheless, among-population variability in egg size was related to environmental conditions. Mean egg size decreased with increasing latitude/decreasing mean annual temperature, contrary to our predictions. However, as predicted, egg size decreased with increasing lake productivity following adjustment for the latitudinal/temperature effect. These results sug- gest that egg size in fishes may be influenced by multiple environmental factors across populations, as well as by maternal effects within populations.

Maternal and Environmental Gradients in the Egg Size of an Iteroparous Fish

Life history theory predicts that organisms inhabiting environments with relatively poor conditions for the growth and survival of their offspring should produce fewer and larger offspring. We examined egg size (an index of offspring size) of an iteroparous, broadcast-spawning, freshwater fish—the walleye (Stizostedion vitreum)—from 34 populations across 26° of latitude in order to determine whether egg size varied with respect to environmental indices of juvenile habitat quality. Variation among populations (among environments) was compared to variation within populations (among females). Within populations, egg size generally increased with maternal size and age. Slopes of these relationships were much more variable among populations (cv > 100%) than interannually within populations (cv < 50%). Egg size vs. female size/age correlations were stronger in populations closer to the northern and southern limits of the walleye range. Egg size was also related to maternal growth history, but the effects of recent growth (previous year) were inconsistent. Egg size varied much less than fecundity among females of the same population. For a standard size/age of female, predicted egg size was more variable among populations (cv > 10%) than interannually within populations (cv < 5%), but only slightly more variable than among females within populations (mean cv = 8.5%). Nevertheless, among-population variability in egg size was related to environmental conditions. Mean egg size decreased with increasing latitude/decreasing mean annual temperature, contrary to our predictions. However, as predicted, egg size decreased with increasing lake productivity following adjustment for the latitudinal/temperature effect. These results suggest that egg size in fishes may be influenced by multiple environmental factors across populations, as well as by maternal effects within populations.

Does Within-Population Variation in Fish Egg Size Reflect Maternal Influences on Optimal Values?

Does Within-Population Variation in Fish Egg Size Reflect Maternal Influences on Optimal Values?

Size of eggs and duration of embryogenesis in fishes

Studies were undertaken on the relationship between egg size and duration of embryogenesis in four freshwater fish species (Salmo trutta L, Esox lucius L., Gasterosteus aculea­ tus L., Leucaspius delineatus Heck.). Analyses were carried out in a comparative sense (different taxa) as well as with re­ spect to eggs of the same species, or even laid by the same female. In addition to understandable differences of egg size between particular species, considerable differences were ob­ served as regards egg size in fish of the same species, and even originating from the same female. In extreme cases the differences in egg size of the same female reached up to 11 percentage points (linear size) and over 40 (volume)! A strict relationship was found between duration of em­ bryonic development and egg size: the smaller the egg, the shorter its embryogenesis. Biological meaning of this phe­ nomenon has been discussed.

Parental Care and the Evolution of Egg Size in Fishes

The quality of parental care appears to correlate positively with egg size, both among and within species of fishes. Past models of the trade-off between quantity and quality of offspring have been inadequate in explaining this correlation. Using features of models by Smith and Fretwell (1974), Shine (1978), and Taylor and Williams (1984), we constructed a model to explain continuous covariation between the quality of parental care and egg size. Our model contains three major assumptions about the dependence of offspring survival on egg size: offspring from larger eggs develop more slowly and take longer to resorb their yolk sacs and become juveniles; egg size determines initial juvenile size; and larger juveniles, which hatch from larger eggs, have lower mortalities, experience faster growth, and take less time to become adults. Under these assumptions, as parental care reduces instantaneous egg mortality, the optimal egg size increases. This increase is expected both among and within populations. Thus, the general conclusion that each population should have a single optimal egg size (see, e.g., Smith and Fretwell 1974; Maynard Smith 1978) may be incorrect.