Malcolm H. Taylor

Lunar synchronization of fish reproduction

Abstract Lunar-synchronized spawning has been reported in four orders of fish. Salmoniform, atheriniform, and tetraodontiform species spawn intertidally on spring tides, leaving their eggs exposed to air between tidal inundations. This spawning mechanism may be essential to survival of species that are residents of areas such as tide marshes where dissolved-oxygen concentrations in the water column can be near zero. Spawning cycles of both lunar and semilunar periods have been reported in coral-reef fishes of the Perciformes. Reproduction by these fishes does not include aerial incubation of eggs. It has been hypothesized that the spawning cyclicity in these fishes synchronizes reproduction with moonlight or current conditions that enhance parental care or predator avoidance. The intertidal spawners that have been studied display cyclic changes in gonad maturity consistent with a semilunar periodicity in recruitment of oocytes into final maturation. Oocytes in the early stages of vitellogenesis are presen...

Lunar Spawning Cycle in the Mummichog, Fundulus heteroclitus (Pisces: Cyprinodontidae)

Spawning in a natural population of the mummichog, Fundulus heteroclitus, occurs cyclically throughout its reproductive season. Gonadal maturity and spawning readiness of males and females are greatest for several days coincident with new or full moon. The spawning rhythm is apparent in size distributions of fry collected during the spawning season. A diurnal cycle in both spawning readiness and gonadal maturity was superimposed on the lunar spawning rhythm. Although mature eggs were found in the ovaries of fish examined during the day at spawning peaks, these eggs were usually dispersed throughout the stroma of the ovary. Fish sampled at the night high tide usually contained ovulated eggs grouped posteriorly in the lumen of the ovary, at the opening of the ovipositor. This rhythmicity synchronizes spawning with the highest tides of the lunar cycle, and makes possible the deposition of eggs in locations which insure their incubation away from strong tidal currents. The observed spawning rhythm is an important component of a reproductive sequence that appears to be of adaptive significance in the tide marsh environment.

Seasonal and daily cycles in sound production associated with spawning in the weakfish,Cynoscion regalis

SynopsisHydrophone recordings were made to document the daily and seasonal cycles of weakfish,Cynoscion regalis (Sciaenidae), sound production in the Delaware Bay. Recordings were made at three stations perpendicular to the shore and rated qualitatively on a scale of 0–4. ‚Drumming’ (sonic muscles, males only) and ‚chattering’ (pharyngeal stridulation, both sexes) were tallied separately. Weakfish were collected from the field throughout the spring and summer to monitor the reproductive status of the population. A clear seasonal trend was noted in both drumming and chattering activities. Drumming activity rose abruptly in mid-May to maximal levels, which were maintained through late June, then dropped off in July and ceased in August. Chattering activity began abruptly in late June, then rose through July and remained high in August. Seasonal drumming activity was more intense at the inshore station. On a daily scale, drumming activity was at its lowest level during the early to mid-morning, then increased to maximal levels in the early evening and remained high until the following morning. There was no daily trend in chattering activity. Daily drumming activity was also most intense at the inshore station. Male and female reproductive readiness, determined by gonadosomatic indices, sperm motility and plasma androgen levels, peaked within the period of maximal seasonal drumming activity.

The role of cortisol in stress-induced metabolic changes in Fundulus heteroclitus

Abstract Adult male Fundulus heteroclitus were found to respond to a number of nonspecific stress stimuli with transient elevations in serum cortisol levels. Metyrapone treatment suppressed stress-stimulated peaks but did not alter resting cortisol levels. Metyrapone elevated serum “11-deoxycortisol” levels. In a 30-hr stress experiment, fasted fish exposed to restraint stress exhibited marked hyperglycemia. Metyrapone-treated fish exposed to the same stress responded with an initial hyperglycemia but did not exhibit the sustained peak seen in untreated fish. Liver glycogen concentrations in stressed fish were somewhat higher than in metyrapone-treated, stressed fish. No significant changes occurred in muscle glycogen, serum protein, or amino acid content of serum, liver, or muscle in stressed fish. Cortisol appears to function during stress in this species to sustain the elevation in serum glucose.

The effects of cortisol treatment on carbohydrate and protein metabolism in Fundulus heteroclitus.

Abstract In male Fundulus heteroclitus captured during the fall, 5 daily injections of cortisol (200 μg/fish or approximately 20 μg/g body wt) produced significant elevations in serum cortisol and hyperglycemia in both fed and fasted fish. Only fasted fish responded with an increase in liver glycogen. No consistent changes attributable to hormone injection occurred in serum protein, amino acid, liver protein, liver amino acids, or liver alanine aminotrasferase. A single cortisol injection (20 μg/g body wt) in fasted fish produced elevated blood glucose levels which persisted for 48 hr and followed serum cortisol changes closely. Again, no significant changes were seen in liver glycogen or in protein metabolism. We conclude that in F. heteroclitus , blood glucose is the major carbohydrate reservoir influenced by cortisol elevation. Protein catabolism appears not to be the source of the glucose elevation. Reduced peripheral glucose utilization and gluconeogenesis from lactate or glycerol are suggested as alternative sources.

Oocyte maturation in the mummichog (Fundulus heteroclitus): effects of steroids on germinal vesicle breakdown of intact follicles in vitro.

The effects of several steroids on the maturation of follicle-enclosed oocytes of the mummichog Fundulus heteroclitus in vitro were examined. At a relatively high concentration (1.0 microgram/ml), a number of different steroids, including pregnenolone, 17 alpha-hydroxypregnenolone, corticosterone, cortisol, 11-deoxycorticosterone, 11-deoxycortisol, androstenedione, testosterone, progesterone, 17 alpha-hydroxyprogesterone, 20 beta-dihydroprogesterone, and 17 alpha-hydroxy-20 beta-dihydroprogesterone, were able to induce germinal vesicle breakdown (GVBD) in prematuration oocytes. Cholesterol, 17 beta-estradiol, 11-ketotestosterone, and 11 beta-hydroxytestosterone were totally ineffective. In general, 11-oxysteroids tended to be less effective than their 11-deoxysteroid counterparts. Two 20 beta-dihydroprogestins--17 alpha-hydroxy-20 beta-dihydroprogesterone and 20 beta-dihydroprogesterone--were the most potent maturation-inducing steroids, initiating 50% GVBD at 1 ng/ml in follicles obtained from ovaries containing mature or maturing follicles in vivo, or at 2.5-4.0 ng/ml in follicles from ovaries lacking mature or maturing oocytes in vivo. These results are consistent with several previous studies involving salmonids and various other teleosts, and suggest a possible physiological role for a 20 beta-dihydroprogestin in the resumption of meiotic maturation in F. heteroclitus.

Ovarian Changes during the Lunar Spawning Cycle of Fundulus heteroclitus

nual intervals is a relatively common phenomenon in shallow water fishes. The guppy, Poecilia reticulata and mosquitofish, Gambusia sp. produce young at approximately 30-day intervals (Turner, 1937). The California grunion, Leuresthes tenuis (Clark, 1925) has a semilunar reproductive cycle in which spawning occurs in synchrony with the spring tides of new and full moon during a reproductive season of several months. Recent field observations on the mummichog, Fundulus heteroclitus (Taylor et al., 1979)

Semilunar changes in estradiol and cortisol coincident with gonadal maturation and spawning in the killifish Fundulus heteroclitus

Radioimmunoassay techniques were used to measure estradiol-17 beta (E2) and cortisol in the serum and ovarian fluid of Fundulus heteroclitus throughout complete semilunar spawning cycles. The cyclic nature of spawning activity was confirmed by monitoring the gonadosomatic index and noting the times at which ovulated eggs were found within the ovarian lumen. Levels of serum E2, ovarian fluid E2, and serum cortisol all exhibited cycles which paralleled the semilunar cycle of gonadal maturity and spawning in this euryhaline killifish. Elevations of serum cortisol were temporally associated with ovulation, whereas ovarian fluid E2 levels peaked several days prior to ovulation. Serum E2 remained elevated after ovarian fluid E2 levels had returned to baseline. Cortisol concentrations in ovarian fluid did not cycle and no correlation was apparent between serum cortisol and glucose concentrations.

Spawning Site Utilization in a Delaware Population of Fundulus heteroclitus (Pisces: Cyprinodontidae)

Populations of Fundulus heteroclitus in mid-Atlantic salt marshes are known to deposit eggs on the marsh surface in empty shells of the Atlantic ribbed mussel (Geukensia demissa). Experimental placement of eggs in this location was associated with normal development and hatching, whereas placement of eggs in tidal ditches resulted in developmental arrest or death of the eggs. Eggs placed in the ditches were subject to siltation and extended periods of immersion in water of less than 2.0 ml/L dissolved oxygen. We have quantified the distribution of both eggs and G. demissa shells in seven 10 m deep plots along ditches in a Delaware marsh. Empty shells were unevenly distributed but were found over the entire 10 meters at densities as great as 10 per M2, with the greater numbers usually occurring beyond 2 m from the ditch. Shells located 1-10 m from ditches were used as spawning sites with a maximum mean of 2.7 ? 1.1 spawns/m2 occurring in the fifth meter of a heavily used plot. Our results suggest that the distribution of spawning in shells is influenced by height of the mussel shell in relation to tidal inundation, as well as size and condition of the shell, and possibly by plant distribution.

Seasonal measurements of serum glucose and serum cortisol in a natural population of Fundulus heteroclitus L

Abstract 1. 1. Seasonal measurements of serum glucose from field populations of Fundulus heteroctitus reveal two peaks; one during the winter months which appeared to be temperature dependent and a second during the summer, correlated with the spawning season. 2. 2. Serum cortisol levels were measured using a radioimmunoassay procedure. No consistent seasonal trends were evident and, in general, cortisol levels were variable throughout the study. 3. 3. There were no statistically significant differences between male and female fish for either of the components measured. 4. 4. Serum cortisol levels were lower than those reported in the literature for this species and were not affected by fish size. There was no simple direct relationship between salinity and serum cortisol levels.