Drag coefficient estimates from coasting bluegill sunfish Lepomis macrochirus

The drag coefficient bluegill sunfish Lepomis macrochirus was estimated from coasting deceleration as (mean ± SD) 0.0154 ± 0.0070 at a Reynolds number of 41,000 ± 14,000. This was within the coasting range in other species and lower than values obtained from dead drag measurements in this species and others. Low momentum losses during coasting may allow its use during intermittent propulsion to modulate power output or maximize energy economy.     

Body length variation within multi-species fish shoals: the effects of shoal size and number of species

Theory predicts that selection should favour phenotypic homogeneity in fish shoals, and field studies have indeed confirmed that variation in body length within fish shoals is significantly lower than expected from a random distribution of fish among shoals. We investigated the extent to which variation in fish body length within shoals is determined by the shoal mean of body length, the number of species in a shoal, and the overall shoal size. We collected 34 fish shoals, ranging in size from 6 to 776 individuals, from the littoral zone of a Canadian lake. Shoals consisted of up to four different species, with multi-species shoals being larger and more frequent than single-species ones. The strongest determinant of body length variation within shoals was the shoal mean of body length, followed by the number of fish species in a shoal; i.e. multi-species shoals were less size-assorted than single-species ones. A more detailed analysis showed that the higher body length variation observed in multi-species shoals was due to increased body length variation both within and between component species. Shoal size had no significant effect on body length variation within shoals. Potential explanations of the positive relationship between body length variation and the number of species in a shoal are suggested. The implications of the above results for the evolution of multi-species shoals are discussed. Received: 6 May 1997 / Accepted: 14 October 1997     

Shoaling preferences of two common killifish (Fundulus heteroclitus and F. diaphanus) in the laboratory and in the field: A new analysis of heterospecific shoaling

Heterospecific grouping behavior of mummichogs (Fundulus heteroclitus) and banded killifish (Fundulus diaphanus) was analyzed in the laboratory and in a freshwater tidal marsh in Cremona, Maryland. Several parameters of wild, intact shoals were measured, including species composition, body length, parasite load, gender, and any physical abnormalities. Fish collected were used for laboratory analysis of shoaling preferences. When size was equal, banded killifish and mummichogs preferred conspecific shoals to heterospecific shoals, consisting of mummichogs, banded killifish, and sheepshead minnows (Cyprinodon variegates). Shoal collection from the field resulted in mixed species shoals with individuals predominantly unaffected by parasites or other physical abnormalities. Size appeared to be a sorting mechanism. A temporal shift in lengths was evident. Initial shoals caught contained significantly smaller fish compared to the final shoals caught. Results are compared with previous studies on heterospecific shoaling in killifish and new characteristics of heterospecific shoals inhabiting freshwater tidal marshes are discussed.     

Increased performance of offspring sired by parasitic males in bluegill sunfish

Males of many species are characterized by alternative matingtactics. In bluegill sunfish (Lepomis macrochirus), some malesdelay maturation and become "parentals" while other males matureprecociously and become "cuckolders." Parentals use an overt,territorial mating tactic, defending a nest and courting females.Cuckolders instead use a sneaking tactic to parasitize parentals.It has previously been shown that parentals that are heavilycuckolded provide less care to their young, yet females do notappear to discriminate against cuckolders, and they may actuallyrelease more eggs when a cuckolder is present than when spawningonly with a parental. Here I examined growth rate of fry ofknown paternity through the yolk-sac stage of development usingcomplementary laboratory and field studies to assess a potentialindirect benefit for females that mate with cuckolders. Comparisonof maternal half-siblings sired in vitro shows that cuckolderoffspring grow faster and to a larger size than parental offspringwhile feeding endogenously on their yolk sac. Because both foodresource and maternal genes are equivalent across treatments,these data indicate a genetic difference in growth between thetwo male life histories. In the field, fry from nests that haveproportionately more cuckolder offspring are larger when theyemerge from the nest. This increased size can lead to threefoldhigher survivorship for cuckolder offspring than parental offspringfrom Hydra canadensis predation, a major predator of bluegillfry. These results are discussed in the context of mate choicefor direct and indirect benefits and in the context of the evolutionof alternative mating tactics.     

Size-assortativeness in multi-species fish shoals

Theory predicts that fish should assort in shoals on the basis of similar phenotypic traits to minimize predation risk and to maximize foraging efficiency. A single phenotypic character, body size, was considered and the hypothesis tested that free-ranging fish shoals are sizeassorted. Furthermore, a second test investigated whether fish within multi-species shoals are more strongly size-assorted with conspecifics than with heterospecifics. Twelve fish shoals, each comprising two different species (golden shiner Notemigonus crysoleucas , and banded killifish Fundulus diaphanus ) were caught in the littoral zone of a north temperate lake using a beach seine. Shoal membership size ranged from 36 to 776 fish, and mean standard body length of members ranged from 18 to 34 mm. Fish were assorted by body size at two different levels, namely, between shoals and at the level of species within shoals. Body sizes of shiners and killifish within shoals were significantly different in seven out of 12 shoals, with killifish being the larger species in five cases and shiners being the larger one in two cases. Because there is considerable overlap in body size between the two species in the population, the observed species-related size-assortativeness within shoals was not just the by-product of a directional size difference (between species) in the population. These findings provide strong quantitative evidence for size-sorting in free-ranging fish shoals and raise questions concerning the formation of multi-species fish shoals.     

Bluegill Lepomis macrochirus synchronize pectoral fin motion and opercular pumping

The relative timing between operculum and pectoral fin motion was examined in swimming bluegill Lepomis macrochirus to determine if respiratory fluid flows from the operculum might have an effect on flow over the pectoral fin. Five bluegill were filmed swimming at speeds from 0·5 to 1·5 body (total) lengths s⁻¹. The timing of opercular pumping and pectoral fin beating was noted and analysed using circular statistics. Fish tended to ventilate their gills every second or third pectoral fin beat. While locomotion and ventilation had different frequencies, however, they were synchronized: fish maintained a consistent phase relationship between them. Thus, within pectoral fin beats when the operculum pumps, the jet consistently occurred during pectoral fin abduction, ending just after the fin was fully abducted and beginning adduction. Based on the distance between the opercular slit and the pectoral fin base, the jet was estimated to reach the fin during maximum abduction. Dye flow visualization confirmed this estimate, revealing that the opercular flow wraps around the base of the fin during peak abduction, when it is likely to have little hydrodynamic effect.     

Juvenile convict cichlids shoaling decisions in relation to shoal size and age

Many animals form groups and socialize in response to evolutionary pressures such as predation, food availability, and mate acquisition. Evidence of social choice based on various phenotypic characters (Group Phenotypic Composition [GPC]) has been observed in several animal species. In addition to the physical characteristics of the social group, it is also interesting to consider how decisions of who to socialize with might be expected to change for an individual over time. Younger individuals with limited life experience may discriminate differently between social groups than older conspecifics who have had the opportunity to learn and who may be faced with different ecological or environmental pressures. Here, we used a traditional two‐choice design to explore the shoaling behavior of juvenile convict cichlids and determine whether the number of fish and/or the size/life stage of the individuals within a shoal influenced social choices. We found that juvenile convict cichlids spent more time shoaling with similarly sized juvenile individuals and also preferred to shoal with larger shoals, but not when shoals were comprised of adult fish. The size of the individuals in a shoal was a more influential factor than the size of the shoal itself. Size of individual juveniles was correlated with tendency to visit shoals, but was not correlated with overall time spent shoaling, regardless of shoal composition. As juveniles, convict cichlids can make discriminatory choices that are influenced by specific aspects of shoal composition.     

Data acquisition and evaluation in biological monitoring systems

Biological monitoring is a means of assessing the quality of water or wastewater. One such method, which enables continuous and automated monitoring, assesses the ventilatory rates of fish as an early warning system. The various methods for data acquisition and data analyses are discussed and compared.     

Scale formation in selected fundulid and cyprinodontid fishes

Patterns of scale formation (onset, points of origin, completion, and spatial pattern) were examined for six species of killifishes in two families (Cyprinodontidae: Cyprinodon variegatus, and Fundulidae: Fundulus confluentus, F. heteroclitus, F. luciae, F. majalis, and Lucania parva) to determine if the patterns are another useful indicator for the transition from the larval to juvenile periods. In some species, the patterns were very similar, with scale formation originating on/near the caudal peduncle, then the dorsal surface of the head (in fundulids only), and later on the lateral surfaces of the head, and on the ventral surface of the trunk at the level of the pectoral fin. The timing of scale formation, relative to fish size, was later than or overlapped with other morphological characters (e.g., fin ray formation, juvenile/adult body shape) often used to mark the larval/juvenile transition. The onset of scale formation, across all species, occurred between 8 and 13 mm TL. Completion of scale formation occurred between 18 and 23 mm TL. At completion, scales covered 86–99% of the trunk and head. Completion of scale formation in these fishes is one of the last external morphological changes to occur during the larval to juvenile transition. For these species, and other flatfishes we have examined in detail, it appears that scale formation may be useful in helping to define the end of the larval period and the beginning of the juvenile period. Further studies, of divergent groups of teleosts, are necessary to determine if this length-based approach has broad validity.     

Lateral migrations of fishes between floodplain lakes and their drainage channels at the Lower Rhine: diel and seasonal aspects

Although the total migratory activity of fishes from floodplain lakes in the Lower Rhine (Germany) into the connected drainage channels, estimated using electrofishing, fyke nets and visual observations, was low during summer 1997, conspicuous diel migrations of adult bream Abramis brama in June and July were recorded in one of the channels studied. A considerable proportion of the population of the floodplain lake immigrated into the channel at dusk and left it at dawn. During two winters (1994–1995, 1997–1998) the abundance of fishes increased considerably in the channels. The winter migrations, studied in detail in one of the channels in 1997–1998, started in late October, when the water temperature dropped below 10° C. In contrast to the mean of 500 fishes per 100 m channel length between May and October, >5000 fishes were found from November to March, with maximum values of >50 000 fishes per 100 m channel length in February 1998. More than 90% of these shoals were 0+ year fishes, dominated by roach Rutilus rutilus , bream, perch Perca fluviatilis and rudd Scardinius erythrophthalmus . These shoals entered the channel at sunrise and left it around sunset. Generally, the 0+ year fishes in the shoals swam separately from the older fishes, and different reactions towards the attack of predatory fishes were observed. The migrating shoals of juvenile fishes during the winter were interpreted as a strategy to minimize predation risk.     

Nucleotide sequence of BamHI family satellite DNA and its unit length polymorphism in bluegill sunfish Lepomis macrochirus

We have isolated and sequenced a member of tandem repetitive DNA containing BamHI site (BamHI family satellite DNA) from bluegill sunfish Lepomis macrochirus. PCR amplification with specific primers was performed to define the size of unit length repeat of the BamHI family satellite DNA, revealing that there were two distinct size of DNA fragments (0.9 kb and 1.3 kb) in the PCR products. The longer fragment (1.3 kb) consisted of internal sub-duplication of shorter fragment (0.9 kb). We have compared the size of PCR products among four fish populations, and found that both fragments co-existed in one population whereas the longer fragment was dominant in other three populations. The results may reflect ongoing homogenization of satellite DNA type over a short evolutionary time scale.     

Origin and dispersal of bluegill sunfish, Lepomis macrochirus, in Japan and Korea

The bluegill sunfish, Lepomis macrochirus, is a notorious exotic species in many freshwater ecosystems, currently expanding its distribution worldwide. In 1960, a small group of bluegills captured in the Mississippi River at Guttenberg in Iowa were imported to Japan as a gift from the mayor of Chicago to the Japanese government. The offspring of these fish were released into the wild in Japan and also in Korea. Over 40 years after this first introduction, L. macrochirus now occupies all the freshwater ecosystems of both countries. We compared invading populations of L. macrochirus in Japan and Korea with native populations in the USA, using PCR-RFLP (polymerase chain reaction-restricted fragment length polymorphism) analyses of mitochondrial DNA, to estimate the origin and dispersal of L. macrochirus in Japan and Korea. Five haplotypes of mitochondrial DNA detected in Japanese and Korean populations completely coincided with the haplotypes of the Guttenberg population. Haplotype diversity of invading populations was shown to be highest in populations established in the 1960s, while genetic variability was lower in more recently established populations. Our results suggest that all L. macrochirus in Japan and Korea have originated from the 15 fish first introduced in 1960. Low haplotype diversity in newly established populations is probably due to genetic drift arising from repeated population bottlenecks, while the high similarity of haplotypes among neighbouring populations is considered to reflect the history of transplantation by humans.     

The effect of sex and shoal size on shoaling behaviour in Danio rerio

Male and female zebra fish Danio rerio were given choices of shoals that differed in sex and size. Male zebra fish preferred to associate with female shoals over male shoals, but had no preference when given a choice between a mixed‐sex shoal and either a male or female shoal. Female zebra fish showed no significant preference when given a choice between male and females shoals, nor between mixed‐sex shoals and either male or female shoals. When given choices between shoals of differing size, females preferred to associate with the larger shoal, whether or not they were composed of males or females. Males, however, had no preference for larger shoals over smaller shoals, whether or not they were composed of males or females. These results showed that male zebra fish were capable of distinguishing between males and females solely on the basis of visual cues. Furthermore, these results demonstrated a significant difference between the shoaling choices of male and female zebra fish, which may indicate a difference in the function of shoaling for the two sexes.     

Crcadian and Seasonal Variations of Lipogenesis in the Gulf Killifish,Fundulus Grandis

Lipogenesis was measured in male Gulf killifish at three seasons under different environmental conditions. Cold temperature is stimulatory for lipogenesis in the fall and spring, but warm temperature is more stimulatory during the summer. The highest rate of lipogenesis occurs during the spring. However, total body fat content is relatively low at that time, which suggests that lipids are being actively mobilized as well. A high rate of lipogenesis also occurs at a cold temperature (20°C) during the fall, and more lipids are stored at that time of year, as evidenced by higher liver and body fat stores. Both lipogenesis and total body fat content are at a minimum during the summer. These results indicate that high levels of lipid synthesis do not necessarily result in higher body fat content, as the latter is the product of both lipid synthesis and lipid mobilization. This study is also in agreement with previous studies which had indicated a changing responsiveness to temperature during the annual cycle of the Gulf killfish.     

Crcadian and Seasonal Variations of Lipogenesis in the Gulf Killifish, Fundulus Grandis

Lipogenesis was measured in male Gulf killifish at three seasons under different environmental conditions. Cold temperature is stimulatory for lipogenesis in the fall and spring, but warm temperature is more stimulatory during the summer. The highest rate of lipogenesis occurs during the spring. However, total body fat content is relatively low at that time, which suggests that lipids are being actively mobilized as well. A high rate of lipogenesis also occurs at a cold temperature (20°C) during the fall, and more lipids are stored at that time of year, as evidenced by higher liver and body fat stores. Both lipogenesis and total body fat content are at a minimum during the summer. These results indicate that high levels of lipid synthesis do not necessarily result in higher body fat content, as the latter is the product of both lipid synthesis and lipid mobilization. This study is also in agreement with previous studies which had indicated a changing responsiveness to temperature during the annual cycle of the Gulf killfish.     

Influence of familiarity on shoaling behaviour in Texas and blacktail shiners

The Texas shiner Notropis amabilis and the blacktail shiner Cyprinella venusta demonstrated statistically significant preferences for the side of the tank holding their familiar shoalmates, and significantly stronger shoaling behaviour with their familiar shoalmates, than with unfamiliar fish.     

The relationship between foraging and shoal position in a mixed shoal of roach (Rutilus rutilus) and chub (Leuciscus cephalus): a field study

Feeding rates of mixed shoals of juvenile roach and chub were observed in a shallow stream near Cambridge (UK). Roach at the front of the shoal had significantly higher feeding rates than roach at the back and than chub in either front or back positions. Position in the shoal also had a significant effect on the kind of food consumed, with front roach feeding more on plankton and back roach more on bottom food. Altogether 36 fish from the stream were caught and marked. Half of these were deprived of food and the other half well-fed for 3 days in captivity. After release 36% of them joined their old shoal again. Individuals from the starved group occupied front positions significantly more often than well-fed fish, but after 2 days this difference disappeared.     

Utilization of the exotic cladoceran Daphnia lumholtzi by juvenile fishes in an Illinois River floodplain lake

Daphnia lumholtzi comprises a substantial component of the zooplankton community during mid‐ to late‐summer in Lake Chautauqua, a floodplain lake along the Illinois River near Havana, Illinois. In order to quantify the utilization of D. lumholtzi by juvenile fishes, diet analyses were conducted for seven juvenile fish species collected from Lake Chautauqua during the 2001 annual drawdown period. Freshwater drum Aplodinotus grunniens and emerald shiner Notropis atherinoides demonstrated negative selectivity for D. lumholtzi relative to native zooplankton species whereas four species of fish (bluegill Lepomis macrochirus, white bass Morone chrysops, white crappie Pomoxis annularis and black crappie Pomoxis nigromaculatus) consumed substantial amounts of D. lumholtzi. Although selectivity values for D. lumholtzi varied among these fish species, positive selection for D. lumholtzi increased similarly among larger size classes of each fish species, and corresponded with ontogenetic shifts in diet. Mean body length of D. lumholtzi consumed by 20–69 mm L_T juvenile fishes ranged from 0·75 to 0·99 mm with a calculated total length range of 2·0–2·6 mm. Results from this study provide evidence that high abundances of D. lumholtzi in mid‐ to late‐summer provide an additional food source for several juvenile fish species during a time when abundances of large native cladoceran species (i.e. Daphnia) are low, and juvenile fishes are searching for larger prey associated with ontogenetic shifts from zooplankton to macroinvertebrates and fishes. Because zooplankton production is typically lower in rivers than in lakes, survivorship of juvenile fishes produced in floodplain lakes may be higher in riverine systems if they are not reliant on zooplankton as a primary food resource. Therefore, high abundances of D. lumholtzi may benefit juvenile fishes in managed floodplain lakes, such as Lake Chautauqua, by increasing growth and facilitating the transition from zooplanktivory to insectivory or piscivory.