Aggregation and spawning of the humphead wrasse Cheilinus undulatus (Pisces: Labridae): general aspects of spawning behaviour

The humphead wrasse Cheilinus undulatus formed resident spawning aggregations daily after high tide at specific locations along the seaward edge of the Palau barrier reef. The location and extent of one aggregation site remained consistent for 6 years with no physical features distinguishing it from adjacent areas. Spawning was documented most months and probably occurred year round with possible seasonal and lunar variation. Spawning males arrived first at the site, followed by females and potentially small primary males. The aggregation female to male sex ratio was estimated to be between 6:1 and 10:1. A maximum of 15 males and 100–150 females were observed at the site. A male courtship posture with the anal fin pointed, the caudal fin folded down and the dorsal fin folded against the body was maintained while swimming a few metres off the bottom in view of females. When ready to spawn females rose up as the posturing male passed and the pair released gametes in a relatively sedate fashion near the surface along the shelf break. No attempted predation on spawning adults was seen. Egg predation after spawning was uncommon. On days with early to mid‐day high tides the spawning period started 2·0–2·5 h after high tide when the speed of lagoon–ocean tidal currents peaked and lasted c. 1 h. On days with later afternoon high tides, spawning occurred sooner after high tide and before current speeds peaked. Other fishes with planktonic eggs spawned at the site as pairs or small groups in a rough succession after high tide with C. undulatus, the last species to spawn.     

Aspects of the spawning of labrid and scarid fishes (Pisces: Labroidei) at Enewetak Atoll,Marshall Islands with notes on other families

Synopsis Spawning of 32 species of Labridae and 13 species of Scaridae was seen at Enewetak Atoll, Marshall Islands. Most spawned on a reef bisecting the main ocean-lagoon passage which had strong tidal currents. Others spawned on lagoon reefs and in Halimeda beds. Polygynous haremic, lek-like and promiscuous mating systems were found which were species specific. Data on reproductive patterns, sexual dichromatism, sexual dimorphism, seasonality and spawning behavior were determined. Many spawned during the day in a time-phase dependent pattern from near sunrise to sunset. Scarid spawning began at slack high water or after when currents were starting to move out of the lagoon. Labrid spawning usually started about 30 min later with some continuing up to 2 h after high tide. With high tide before sunrise, scarid spawning began 30–50 min after sunrise as the current started flowing over the reef. With high tide near sunset, spawning occurred with an incoming current. Most labroids spawned on all phases of the moon. Acanthuridae (6 spp), Caesionidae (1 sp.) and Zanclidae (1 sp.) spawned after high tide at the same time as labroids. Pomacanthidae (5 spp.) spawned only shortly before sunset without reference to tidal currents. Fishes producing pelagic eggs at the lagoon-ocean channel spawned (1) at or slightly after high tide (44spp.), (2) in late afternoon without reference to tide (6 spp.) or (3) after slack low water (1 sp. ). Spawning style can vary within a single species in different environments. Despite the presence of many piscivores, no successful predation on spawning adults was seen. Predation on newly released eggs was uncommon. Labrichthys unilineata and Anampses twistii attempted to defend their eggs for a few sec after release. Attacks by piscivores on spawning adults on tropical reefs occur once per 100–1000 spawnings. Most are wary when preparing to spawn and prespawning behavior is easily interrupted. The risk from piscivores goes down and spawning ascent speed decreases with increasing size of spawners. Egg predation by zooplanktivores is less for pair spawners than group spawners possibly due to less conspicuous gamete clouds and times of spawning. Increasing height of egg release, speed and length of the spawning ascent, and trajectory alteration of ascending adults are believed to make it more difficult for zooplanktivores to locate eggs after release. For labrids, permanent full sexual dichromatism was found among haremic, lek-like and promiscuous mating systems. Species with temporary full dichromatism, permanent and temporary partial dichromatism and monochromatism were haremic. Smaller scarids were believed to have lek-like, and larger species haremic, mating systems. Smaller scarids had male looping behavior and post spawning displays, plus faster spawning ascents and different locations for egg release than larger ones. Eggs of 21 labrids were spherical or nearly spherical, ranging from 0.55–0.80 mm in diameter, and most had one oil globule. Among 7 is scarids, 6 had spindle-shaped eggs ranging from 1.25 ×0.50 mm 2.14× 0.48 mm while one had a nearly spherical egg. One scarid egg lacked an oil globule.     

Courtship and spawning behavior of the pygmy grouper,Cephalopholis spiloparaea (Serranidae: Epinephelinae), with notes on C. argus and C. urodeta

Synopsis Courtship and spawning behavior is described for the grouper Cephalopholis spiloparaea from Rota, Mariana Islands. Daily courtship behavior began late in the afternoon and proceeded until after sunset. Males repeatedly visited females in single-male, multiple-female mating groups during each period and engaged in courtship bouts. Mating was observed only twice, was paired and pelagic. Two congeners, C. argus and C. urodeta, with overlapping geographical distributions, were also examined. Cephalopholis urodeta appeared to have a mating group organization similar to that of C. spiloparaea, with some similarity in courtship behavior. Cephalopholis argus also had a similar mating group organization but differed in courtship behavior. This species' behavior more closely resembled that of similarity-sized Epinephelus spp.     

Population variation in spawning current speed selection in the blacktail shiner,Cyprinella venusta (Pisces: Cyprinidae)

Synopsis Many stream fishes lay demersal eggs. Some species simply scatter the eggs across the substrate, but many place the eggs in protected sites such as crevices (e.g., Cyprinidae:Cyprinella). Eggs laid in crevices may experience increased development times or lower embryo survival due to reduced water exchange rates compared to more open egg deposition sites. If so, the presence of an appreciable current near the crevice may be important for insuring water exchange. However, currents that are too strong may prevent complete insemination or prevent the eggs from adhering to the substratum before they are washed from the crevice. Thus, current speed preferences for spawning may be under strong stabilizing selection. Representatives of four populations of a crevice spawning stream fish (blacktail shiner,Cyprinella venusta), representing environments ranging from a swift stream to a lake, were studied in stream tanks to evaluate female spawning current use. The observed frequency of use of spawning currents was significantly different from random in all populations. Low current speeds were generally avoided, and a speed of ca. 30 cm sec^–1 was used most often. However, significant differences were observed among populations, and the variation correlated well with the apparent range of current speeds found in the four environments. Although other possible explanations cannot be dismissed, the results are consistent with the hypothesis that the populations have become adapted to their local current regimes.Authorship in order of seniority     

Variation in mating systems and sexual size dimorphism between populations of the Australian python Morelia spilota (Serpentes: Pythonidae)

Although adaptationist hypotheses predict a functional relationship between mating systems and sexual size dimorphism, such predictions are difficult to test because of the high degree of phylogenetic conservatism in both of these traits. Taxa that show intraspecific variation in mating systems hence offer valuable opportunities for more direct tests of evolutionary-ecological hypotheses. Based on a collation of published and unpublished records, we document intraspecific geographic variation in mating systems (presence versus absence of male-male combat) within the widely-distributed Australian python Morelia spilota. Radiotelemetric monitoring of 19 free-ranging pythons in a population in north-eastern New South Wales showed that these animals display a mating system of female defence polygyny. Previous studies on a southern population of the same species found that males engaged in long mate-searching movements, showed no overt agonistic behavior, and formed long-term (>2 months) aggregations around reproductive females. In strong contrast, our adult male carpet pythons (i) moved about relatively little (mean displacement <11 m/day) during the mating season, (ii) remained with females only briefly (<5 days), and (iii) engaged in male-male combat in the vicinity of females. This male-male combat included vigorous biting as well as ritualised wrestling matches, resulting in a high incidence of bite scars in adult males. In keeping with predictions from sexual selection theory, males attain larger body sizes than females in this population, whereas females grow larger than males in the previously-studied southern population where males do not engage in physical combat for mating opportunities.     

Dimorphic growth in male and female cuttlefish<Emphasis Type="Italic"> Sepia orbignyana</Emphasis> (Cephalopoda: Sepiidae) from the Adriatic Sea

The relationships between mantle length and number of cuttlebone chambers (or septa), and between weight and number of cuttlebone chambers were studied in Sepia orbignyana collected in the south-western Adriatic Sea. Weight-at-chamber count and mantle length-at-chamber count were statistically higher in females than in males. As the available literature suggests that the rate of cuttlebone septum formation is the same in both sexes of Sepia species, it follows that in S. orbignyana females have higher growth rates than males. Received in revised form: 6 February 2001 Electronic Publication     

Lunar synchronization of spawning in sea bass, Lates calcarifer (Bloch): effect of luteinizing hormone-releasing hormone analogue (LHRHa) treatment

Based on egg collection records, spontaneous spawning activity of sea bass, Lates calcarifer (Bloch), reared in floating net cages followed a semilunar cycle. The peak of multiple spawnings coincided with declining spring tides of quarter moon periods. Maximum diameter of intra-ovarian, ripe oocytes (0.51–0.55 mm) occurred in synchrony with the quarter moon periods. Smaller oocytes (0.44–0.47 mm) were sampled during the new and full moon periods. Two structural analogues of luteinizing hormone-releasing hormone (LHRHa) (des-Gly¹⁰, d -Ala⁶-LHRH ethylamide and d -Ala⁶, Pro⁹-Nethylamide-LHRH), in pelleted or dissolved form, induced mature female sea bass with a mean egg diameter of at least 0.40 mm to spawn at any day during the lunar cycle. The onset of spontaneous and LHRHa-induced spawnings occurred during low tides in the evening until dawn (from 19.00 to 05.00 hours). These results demonstrate that LHRHa can effectively induce mature sea bass to spawn independent of the highly predictable semilunar spawning rhythm. In addition, the occurrence of both spontaneous and hormone-induced spawnings at a precise period of the day suggest a tidal and diurnal cue entraining spawning of mature female sea bass.     

The courtship and spawning behaviors ofCanthigaster valentini (Tetraodontidae)

Synopsis The sharpnose puffer,Canthigaster valentini, occurs in male-dominated harems of territorial females at Lizard Island (Australia). Spawning occurs daily and year-round. Males only spawn with the females of their social group, inside the female's territory. Females signal their readiness to begin courtship with a display that exposes their egg swollen abdomen. Courtship is long and males do not develop specific courtship colors or perform unique displays. Eggs are fertilized in a demersal nest and there is no parental care.     

Social organization and spawning in the Atlantic sharpnose puffer,Canthigaster rostrata (Tetraodontidae)

Synopsis Social organization and spawning in the sharpnose pufferCanthigaster rostrataere studied on a reef in the San Blas Islands, Panama. Sexes were dimorphic. In mixed coral and rubble habitat, females defended territories against other females and small males. From one to six female territories were included within the territories of certain large males. These haremic males visited their females and patrolled their territories throughout the day. Smaller, non-haremic males occupied territories or home ranges within or adjacent to those of haremic males or were wanderers. Spawning between a haremic male and a territorial female occurred within the female's territory. The female prepared an algal nest into which demersal eggs were deposited. There was no parental care. Eggs were spherical, translucent, and measured approximately 0.66 mm in diameter. Larvae were about 1.4 mm TL and closely resembled those of other species ofCanthigaster.     

First evidence of spawning of eastern Baltic cod (Gadus morhua callarias) in the Belt Sea,the main spawning area of western Baltic cod (Gadus morhua L.)

Two cod stocks (western Baltic cod, WBC, and eastern Baltic cod, EBC) are managed in the Baltic Sea which is characterized by different main spawning areas and different main spawning periods. In this study we analyse the spatial and temporal occurrence of spawning individuals of both cod stocks in the main spawning grounds of the Baltic Sea based on eight microsatellite loci. Our results suggest that EBC (Gadus morhua callarias) has formed currently temporally stable, substantially homogeneous population not only in the Bornholm Sea (ICES SD: 25) but also in the Arkona Sea (ICES SD: 24). The presented analyses proved that EBC (G. m. callarias) can temporarily also spawn in the Belt Sea.     

Field and laboratory observations of spawning periodicity and behavior of a northern population of the Atlantic silverside,Menidia menidia (Pisces: Atherinidae)

Synopsis The spawning periodicity and mating behavior of a northern population of the Atlantic silverside, Menidia menidia, was studied both in the field (Salem Harbor, Massachusetts) and in laboratory experiments. Spawning in the field coincided with new and full moons. Under conditions of unlimited food availability in artificial outdoor pools that received natural celestial illumination or in indoor aquaria receiving no evening illumination, spawning occurred every 1–3 days rather than fortnightly. These results suggest that tidal influences are a primary factor that synchronizes spawning in M. menidia. Published reports of diel time of spawning in both marine and freshwater species of Menidia indicate a generic tendency to spawn during mid-morning. This pattern coupled with high tides that cover suitable spawning substrates during mid-morning only at fortnightly intervals could account for the semilunar spawning cycle in marine populations of Menidia. Although general characteristics of the reproductive ecology of M. menidia in Massachusetts were similar to a thoroughly studied population in South Carolina, several differences were evident. The breeding season was shorter in Massachusetts (late; April–June), and occurred over a much lower range of temperatures (9–21°C). Intensity and frequency of spawning was correlated with the height of high tide. Eggs were deposited only on mats of intertidal, filamentous algae rather than on roots or stems of Spartina alterniflora or other intertidal vegetation. Promiscuous spawning occurred in small, highly male-dominated groups of fish, primarily after the tide had begun to recede, and often at the water's edge. No predation on spawning adults was observed but the mummichog, Fundulus heteroclitus, fed daily on developing embryos during high tide. Contribution No. 81, Massachusetts Cooperative Fisheries Research Unit, Contribution No. 349, Marine Sciences Research Center, State University of New York at Stony Brook.     

Gonadal development and spawning of female ocean whitefish, Caulolatilus princeps (Pisces: Branchiostegidae) in the Bay of La Paz, B.C.S., Mexico

The developmental stages of the gonads and the spawning season of the ocean whitefish, Caulolatilus princeps , were determined. Gonad maturation is annual, and the spawning season is prolonged, from late autumn to early spring. From November to March, around 80% of the females were in an advanced mode of gonadal development, and in April most gonads were spent. From May to October the gonads were at rest and preparing for the next spawning season.
The gonadosomatic index describes the reproductive activity of the species adequately.     

Allopaternal care in the tessellated darter,Etheostoma olmstedi (Pisces: Percidae)

Synopsis Large male tessellated darters, Etheostoma olmstedi, defend flat-bottomed rocks, the undersides of which serve as spawning substrates. Because females attach eggs directly onto bare stone, a spawning bout necessarily decreases the surface area available for further breeding at a nest. In apparent response to the female preference of ovipositing on rocks with the most bare surface, fathers abandon nests with their attached offspring to search for rocks with more uncovered surface. Egg abandonment also results after roving fathers intercept and spawn with ripe females and remain at a different rock to care for a new clutch. In essence, large males appear to maximize the number of eggs they fertilize by sequentially monopolizing breeding patches that are temporarily most desirable to females. The costs to a father of abandoning his eggs appear to be low for two reasons: (1) non-territorial males, created by a scarcity of suitable rocks, readily occupy vacant nests, and clean and aerate the abandoned eggs; and (2) after water hardening, eggs are less vulnerable to cannibalism. The maintenance of eggs by nonparental males may be both incidental to scrubbing the ceiling for their own breeding and adaptive in that viable eggs stimulate females to spawn; neither would appear to involve parental investment costs. Thus, allopaternal care in the tessellated darter may have evolved because it is performed in the selfish pursuit of spawning opportunities while entailing little, if any, of the costs normally subsumed within parental investment.     

Mapping the spawning grounds of North Sea cod (Gadus morhua) by direct and indirect means

Despite recent evidence for sub-stock structuring, North Sea cod are assessed as a single unit. As a consequence, knowledge of sub-stock trends is poor. In particular, there are no recent evaluations of which spawning grounds are active. Here we report results from the first ichthyoplankton survey to cover the whole North Sea. Also, this survey, conducted in 2004, was the first to make extensive use of DNA-based molecular methods to unambiguously identify early developmental stage cod eggs. We compare the findings from the plankton survey with estimated egg production inferred from the distribution of mature cod in contemporaneous trawl surveys. Results from both approaches were in general agreement and showed hot spots of egg production around the southern and eastern edges of the Dogger Bank, in the German Bight, the Moray Firth and to the east of the Shetlands. These areas broadly coincide with known spawning locations from the period 1940 to 1970. We were, however, unable to directly detect significant numbers of cod eggs at the historic spawning ground off Flamborough (northeast coast of England). The results demonstrate that most of the major spawning grounds of cod in the North Sea are still active but that some localized populations may have been reduced to the point where it is now difficult to detect the presence of eggs in the plankton.     

Aquatic surface respiration,an adaptive response to hypoxia in the guppy,Poecilia reticulata (Pisces,Poeciliidae)

Synopsis Aquatic respiration at the air-water interface, herein termed aquatic surface respiration (ASR), is used by the guppy,Poecilia reticulata (Poeciliidae) to meet oxygen demand in hypoxid water. A specific position in which the head contacts the surface and the jaws open just beneath the surface is adopted. ASR is initiated at a P0₂ of about 50 torr and the percent time spent rises in a steep, linear fashion as PO₂ decreases. Below 4 torr more than 90% of the animal's time is spent in ASR. Males spend less time in ASR than do females. The percent time in ASR increases with increasing size of female guppies, but decreases with increasing size of male guppies. At low oxygen (18 torr) laboratory-born guppies derived from stocks likely to experience deoxygenation spend less time in ASR than do guppies derived from stocks less likely to experience deoxygenation. The percent time in ASR increases with temperature when PO₂ is held constant. Acclimation to low oxygen decreases the percent time in ASR.Guppies not permitted ASR die in 6–41 h at 14–17 torr and 10–15 min at 1–4 torr. Guppies performing ASR survive the duration of experiments at 13–35 torr (13 days), 14–17 torr (96 h), and 1–4 torr (9.5 h). Activity, courtship, and dive duration in response to a shadow stimulus are all reduced by low oxygen. ASR is an effective alternative to aerial respiration as an adaptation to hypoxic waters, but is probably energetically and temporally more costly.     

Food habits of the giant humphead wrasse,Cheilinus undulatus (Labridae)

Synopsis The giant humphead wrasse (Cheilinus undulatus), an inhabitant of coral reefs, is widely distributed in the tropical Indo-Pacific region. Stomach and intestinal contents of 72 specimens from the Pacific and the Red Sea revealed that this fish feeds primarily on mollusks, fishes, echinoids, and crustaceans.This article is one of several presented at the Second European Ichthyological Congress, Paris, 8-15 September 1976, to be published by Environmental Biology of Fishes.     

Ecology of some species of catfishSynodontis (Pisces: Mochocidae) in the Kpong Headpond in Ghana

Synopsis Some aspects of the ecology of the freshwater catfishSynodontis (Pisces: Mochocidae) in Kpong Headpond (Ghana) were studied. Five species were encountered, namelySynodontis schall, S. gambiensis, S. ocellifer, S. velifer andS. eupterus. S. ocellifer andS. velifer were not recorded in the area before impoundment and might have entered the headpond as eggs or young from the main Volta Lake. Length: weight relationships for the two most important species can be described by the equations: Log W = - 1.76 + 3.12log L (maleS. schall), Log W = -1.33 + 2.89log L (femaleS. schall) and Log W = - 0.39 + 2.07log L (S. gambiensis, sexes combined).Synodontis is omnivorous and generally browses on benthic deposits. Adults feed mostly on chironomids, plant material and aquatic insects. The genus displays sexual dimorphism by having a short urino-genital papilla in most adult males. ForS. schall, one season of major spawning activity occurs per year from mid to late September with first time spawners between 20.0–30.0 cm SL. TheSynodontis species studied lay between 2000 to 209000 eggs per spawning season.     

Mating system in the tarantula spider Eupalaestrus weijenberghi (Thorell, 1894): evidences of monandry and polygyny

The road tarantula Eupalaestrus weijenberghi shows a strongly female-biased sex ratio since adult females live several years while adult males live only for 2 months. In this scenario selective males could be expected. However, several factors such as the rates of reproduction of each sex, degree of sexual selectivity and synchronicity of female receptiveness determine the operational sexual ratio and mating system of the species. Our objective was to determine the mating rates and mating tactics for females and males of E. weijenberghi and their variation throughout the reproductive period. Four hundred sexual encounters among 20 females and 20 males in all possible pair-wise combinations were carried out during 29 days, a brief but intense experimental period, as it also occurs in the field. Mating success differed strongly between sexes. Females mated once: five females mated at the first attempt, eight initially rejected males and copulated in subsequent attempts. Half of the males did not copulate and the others copulated 1-3 times. Mated females actively rejected males. Results indicate a mating system with monogamous females and polygamous males. Not all the females were receptive in every reproductive season. We suggest that female monogamy drastically affects the operational sex ratio, since several females were unreceptive after a single copulation, directly diminishing the male potential reproductive rate. This is the first experimental approach to estimate tarantula mating systems, their determinants and the consequences of the strategies shown by each sex.     

Postsettlement growth of two estuarine crab species, Chasmagnathus granulata and Cyrtograpsus angulatus (Crustacea, Decapoda, Grapsidae): laboratory and field investigations

The estuarine grapsid crabs Chasmagnathus granulata and Cyrtograpsus angulatus belong to the most typical and dominant inhabitants of brackish coastal lagoons in southeastern South America. In a combined laboratory and field investigation of juvenile growth, we measured the increase in body size in these species under controlled conditions as well as in field experiments (in Mar Chiquita lagoon, Argentina), seasonal changes in size frequency distribution of a natural population, and growth related changes in selected morphometric traits of male and female juveniles (relations between carapace width, carapace length, propodus height and length of the cheliped, and pleon width). At 24°C, Cy. angulatus grew faster than Ch. granulata; it reached the crab-9 instar (C9; 13 mm carapace width) after 92 days, while Ch. granulata required 107 days to reach the C8 instar (7.4 mm). At 12°C, growth ceased in both species. The pleon begins to show sexual differences in the C5 (Cy. angulatus) and C8 instar (Ch. granulata), respectively, while the chelae differentiate earlier in Ch. granulata than in Cy. angulatus (in C4 vs C6). In the field, growth was maximal in summer, and was generally faster than in laboratory cultures. However, there is great individual variability in size (about 25% even in the first crab instar) and in size increments at ecdysis, increasing throughout juvenile growth. Our data indicate that, in the field, small-scale and short-term variations in feeding conditions, temperature, and salinity account for an extremely high degree of variability in the absolute and relative rates of growth as well as in the time to sexual differentiation. Received in revised form: 20 September 2001 Electronic Publication