Photoperiodic regulation of gametogenesis and gonadal growth in the sea star Pisaster ochraceus

A photoperiod regime 6 mo out of phase between December 1978 and August 1980 resulted in gametogenesis, gonadal growth, and spawning in laboratory-maintained sea stars [Pisaster ochraceus (Brandt)] 6 mo out of phase with individuals in the field or laboratory on normal celestial photoperiods at Santa Cruz, California (USA). The seasonal fluctuation of pyloric cecum size also was shifted when the sea stars were held on the out-of-phase photoperiod regime. Phase shift of all these events was evident within 6 to 9 mo. Long daylengths (or short nightlengths) in spring and summer apparently synchronize or entrain the initiaion of gametogenesis and gonadal growth in fall.     

Changes in tissue cholesterol and serum cortisol level during four reproductive phases of the male freshwater fish, Notopterus notopterus

The tissue cholesterol and serum cortisol changes during four reproductive phases has been studied in the freshwater fish Notopterus notopterus of male sex during four phases, preparatory (January - March), prespawning (April - May), spawning (August - September) and post spawning (November - December). The cholesterol content of the testis and liver increased during preparatory phase and maximum content of cholesterol was during spawning phase. The serum cortisol estimated by radioimmunoassay (RIA) technique which indicated that the level of the hormone was high during pre-spawning and spawning phases compared to other two phases. The increase in cholesterol during preparatory and spawning phases may be because of increase in cortisol synthesis needed for testicular growth and spermetogenesis during these phases. The gonadosomatic index (GSI) also increased during these phases.     

Effect of photoperiod on the adrenal activities of male rose ringed parakeet, Psittacala krameri

Adult male rose ringed parakeets were exposed to very long photoperiod (22 hr L: 2 hr D) and very short photoperiod (2 hr L: 22 hr D) daily for 60 days during different phases of the annual testicular cycle. Adrenal activities of the experimental birds were compared with that of parallel held natural photoperiodic birds. Marked atrophy of adrenocortical cells was noted in the glands of long photoperiod (22 hr L:2 hr D) during different phases, i.e., post-breeding, quiescent and pre-breeding phases of annual gonadal cycle. The atrophied cells were not uniformly distributed in different groups of long photoperiod responsive birds. During pre-breeding, post-breeding and quiescent phases marked atrophy of the adrenocortical cells were restricted to the sub capsular zone of the gland. The cytometric and karyometric studies also revealed significant decrease in the cortical cord width and diameter of nuclei in the cortical cells in either subcapsular zone in the gland of long photoperiodic birds considered for treatment during pre-breeding, post-breeding and quiescent phase or in both the sub capsular zone and the inner zone. The cytometric and karyometric values did not show any change from control birds.     

Can photoperiod manipulation affect gonad development of a boreo-arctic echinoid (Strongylocentrotus droebachiensis) following exposure in the wild after the autumnal equinox?

A laboratory experiment was conducted in the winter of 2003–2004 to assess the effect of varying photoperiod regime on consumption rate, assimilation rate, absorption efficiency, and gonad development of the green sea urchin, Strongylocentrotus droebachiensis. Adult individuals were collected from the wild after they had been exposed to the ambient autumn photoperiod cue (which is the extraneous trigger thought to elicit gametogenesis in this species) and placed at ambient temperature for 12 weeks under five different photoperiod regimes: (1) 24 h light:0 h dark=“0D”, (2) 16 h light:8 h dark=“8D”, (3) 8 h light:16 h dark=“16D”, (4) 0 h light:24 h dark=“24D”, and (5) ambient photoperiod (range: 10.50–15.25 h dark). Urchins in these five treatments were fed ad libitum with bull kelp, Nereocystis luetkeana. A sixth treatment consisted of starved individuals held under 0D conditions. Various gonad factors including gonad index, percent gonad water, gonad colour (CIE lightness or L*, CIE hue or a*, and CIE chroma or b*), percent area occupation of the gonad by various cell types (nutritive phagocytes, spermatozoa, and secondary oocytes/ova), and stage of development were assessed at the beginning of the experiment and at weeks 4, 8, and 12 of the study. Consumption and assimilation rates were assessed at weeks 4 and 12 and absorption efficiency at week 12 of the experiment. Urchins were predominantly in the growing and premature stages at the beginning of the experiment, but by week 4 at least 20% of individuals in all treatments receiving food were classified as mature. Spawning occurred during all these treatments between weeks 4 and 8, as evidenced by significant decreases in spermatozoa and secondary oocytes/ova and a significant decrease in percent gonad water, but was not accompanied by major declines in gonad indices. Greater than 90% of individuals in all five of the fed treatments were in the recovering and growing stages at the end of the experiment. The 16D treatment had by far the greatest percentage of urchins in the growing stage. In contrast, individuals that were starved were predominantly in the mature stage at weeks 4, 8, and 12, with only ~30% reaching the spawning stage by the end of the experiment. Photoperiod significantly affected gonad indices at the termination of the experiment with gonad index being the highest in the 16D treatment; this was significantly greater than in the 8D and ambient treatments. Photoperiod did not significantly affect gonad percent water, gonad lightness, or gonad hue. Gonad chroma was significantly affected by photoperiod, urchins held under ambient conditions having significantly lower b* readings than individuals in any other treatment. Photoperiod had little or no affect on consumption rate, assimilation rate, or absorption efficiency. Thus, differences among treatments in regards to gonad index, gonad chroma, and stage of development cannot be attributed to variations in feeding, absorption, or assimilation. The results of this experiment indicate that once gametogenesis is initiated, photoperiod manipulation cannot prevent ultimate spawning. However, photoperiod regime can affect the rate at which urchins move through the various stages of the gametogenic cycle. Urchins placed on short days under artificial lighting (16D) moved through the spawning stage into recovering and growing stages the fastest. This photoperiod regime also produced the highest gonad index at the end of the experiment. Since the commercial urchin market prefers large gonads in the growing and premature stages (i.e. before the mature stage is reached and gonads start leaking sperm and eggs), short day-lengths under artificial lighting (16D) appear to be the best photoperiod conditions for optimizing marketability.     

Plasticity in spawning visits of female damselfish, Stegastes nigricans : effect of distance to mates

Both sexes of the damselfish Stegastes nigricans hold individual territories in which they feed on filamentous algae. At dawn, females visit males' territories to spawn, and the males guard the eggs until hatching. We examined how females' spawning behavior varied according to the distances to their mates. Females usually mated with a single male per morning. The distance to the territory of a mate (0.7–12.8 m) did not affect a female's total spawning time per morning, but affected the number of her spawning visits with that male. Females made many repeated spawning visits when spawning with males at short distances, while they spawned the entire clutch in one visit when spawning with males at long distances. This plasticity in female behavior appears to be related to two costs during the spawning visits: (1) intrusions by other fish to feed on algae in the female's territory during her absence, which may cause the female to return repeatedly to her territory for defense, and (2) attacks on the female by other territorial fish, which increased with the distance to their mates' territories. To minimize the sum of both costs, females should change the number of spawning visits depending on the distance to the males' territories. Received: 30 September 1996 / Accepted after revision: 17 March 1997     

Seasonal ovarian cycle in freshwater teleost, Labeo rohita (Ham.) in Tarai region of Uttaranchal

Seasonal ovarian cycle, based on histophysiological changes, and correlative variations in liver were studied in an Indian major carp, Labeo rohita reared in captivity under ambient environmental conditions in Tarai region of Uttaranchal. The oocyte features used for marking ovarian cycle included nuclear-ooplasmic ratio, yolk vesicle incorporation into ooplasm, number and size of nucleolus and differentiation of follicular layer. Based on these features the ovarian cycle in L. rohita was divided into five phases i.e. resting, preparatory, pre-spawning, spawning and post-spawning/regression. The resting and preparatory phases were characterized by the dominating presence of chromatin-nucleolar and yolk-vesicle stage oocytes. The pre-spawning phase ovary was marked by the prevalence of yolk globule stage oocytes having cortical alveoli and differentiating follicular wall. The oocytes containing densely packed yolk-granules and large masses of yolk vesicles and also exhibiting germinal vesicle movement (GVM) signified the ovary of spawning phase. The ovary in regression phase contained pre-ovulatory atretic oocytes and significant number of oogonia. The histophysiological changes in liver showing augmented biosynthetic activity during preparatory and pre-spawning phases seemed well correlated with the gonadal development. The increasing water temperature and day-length apparently was favourable for the gonadal development in L. rohita.     

Patterns of the electric organ discharge during courtship and spawning in the mormyrid fish,Pollimyrus isidori

Summary Pollimyrus isidori's electric organ discharge (EOD) is of the pulse type. Patterns of EOD intervals were investigated prior to, during and following spawning behaviors as related with overt behaviors, and with the sound production by the nestbuilding male. Prior to the time of reproduction, isolated and socially interacting fish (n=15) showed characteristic discharge interval patterns for resting, swimming, probing, hovering and hiding activities. Males (n=8) and females (n=6) did not differ in their mean EOD repetition rates during resting (11.6±2.5 Hz), nor Short Bursts/min (less than 20 intervals of 8–13 ms). In interacting fish Long Bursts (greater than 20 intervals of 8–13 ms, lasting for more than 300 ms) were observed only during the attack and bite sequence. A pursuing fish displayed a rapid alternation of Long Bursts with Discharge Breaks (300–1000 ms silence) during the chase behavior. Avoidance behavior which followed from several attacks was correlated with a Medium Uniform Rate (8–12 Hz) normally lasting for 20 to 60 s, or a Discharge Arrest (silence greater than 1 s) in the submissive fish. The nocturnal courtship behavior began soon after dark (1900 h). Spawning typically started 2 to 5 h after dark, continuing for 2 to 6 h until about 0200 h. During courtship and spawning the female's brief visits (15–25 s) to the male's territory recurred every 30–60 s. At all other times the female was aggressively excluded from the nest region. Courtship and spawning behaviors are described along with the electrical displays identified from 19 spawnings in three fish pairs (from a total of 37 spawnings in 4 males and 4 females). Just prior to the onset of courtship behavior, with male territorial aggression beginning to decline, females switched from a Medium Sporadic Rate pattern (resting and hiding patterns; 13 Hz) to a Medium Uniform Rate pattern (6–8 Hz) while still in their hiding area. Females continued to display this uniform rate throughout the courship and spawning period, including the courtship and spawning bouts when Discharge Breaks or Arrests also occurred. This persistance distinguishes the courtship pattern from the similar avoidance pattern (see above). The male courtship and spawning EOD pattern was similar to the female's and unique for a territorial male. He switched from a High Sporadic Rate (swimming EOD pattern; about 18 Hz) to a regularized Medium Uniform Rate (about 9 to 11 Hz) only during courtship and spawning bouts, including 1–3 EOD Breaks during Vent-to-Vent coupling (average interval: 272±71 ms, n=37). No sooner had the female left the spawning site than he resumed displaying a High Sporadic Rate. This temporal correlation of reproductive behaviors with electrical displays suggests their instrumental role in mutual acceptance of mates. Males showed their sex-specific type of EOD phase-locking, the Preferred Latency Response, only during the first few hours of entry of a fish in their tank. Two females with EOD waveform features more typical of males also spawned repeatedly; waveform does not appear to be critical. Males stopped their nocturnal sound production for the later part of courtship and the whole spawning period. Except for infrequent attacks on the female between spawning bouts, the male did not resume singing until the end of spawning when all eggs were shed (around 0200 h); from this time on the male sang until dawn. The sequencing of the three acoustic elements (moans, grunts, growls) are described. A catalogue of discharge patterns correlated with overt behaviors (Tables 1, 2), and an integrated summary time table of P. isidori's complex reproductive behavior are presented.     

Mechanisms enabling sperm economy in blenniid fishes

Sperm competition, cost of spermatogenesis and spawning frequency are known to influence ejaculate expenditure. Accordingly, males, particularly those with high reproductive costs, are expected to have evolved mechanisms enabling them to prudently allocate sperm, such as the fractioning of ejaculate expenditure or the semi-cystic type of spermatogenesis, hypothesised to favour the production of small ejaculates. In this study, we investigate sperm competition risk, ejaculate size and mode of ejaculate release in seven polygynous blenniid fish where males provide sole paternal care of eggs. In addition, we estimated the relative size of the two parts composing the male gonad, the strictly testicular (testicular lobules or testis) and the glandular (testicular gland), as the development of the latter is indicative of the level of semi-cystic spermatogenesis. In all the examined species, eggs were laid one by one, and the sperm expenditure at mating, evaluated as the total number of sperm released per mating, was parcelled out in several successive ejaculations, allowing males to adjust the release of sperm to the duration of egg deposition. In accordance with sperm competition theory, species experiencing higher sperm competition risk allocated more in sperm, both considering ejaculate size and ejaculate expenditure per mating. An increase in sperm expenditure was paralleled by the development of the testis at the expense of the testicular gland. Smaller species, whose males do not face sperm competition risk and fecundity is low, produced smaller ejaculates and exhibited a more developed testicular gland, supporting the hypothesis that a semi-cystic type of spermatogenesis is a mechanism allowing sperm economy.     

The pattern of early growth trajectories affects adult breeding performance

Early environmental conditions can influence the pattern of growth and development. While poor conditions generally cause slower growth, normal adult size can still be reached if growth accelerates or is prolonged once conditions improve, but such catch-up growth may have deleterious effects later in life. Here we investigate for the first time how decelerating as well as accelerating growth trajectories, manipulated independently of food supply, affect subsequent breeding performance. In order to alter growth rates we subjected juvenile three-spined sticklebacks Gasterosteus aculeatus to a short period of altered environmental temperature (high, intermediate, or low), after which all fish had the same (intermediate) temperature regime. In addition, the perceived time stress (until the onset of the spawning season) was manipulated by conducting the experiment twice (in the winter and in the spring immediately prior to breeding) and by exposing half of the fish in each experiment to a delayed photoperiod (two months behind ambient). We found that fish showed full growth compensation, such that in all treatments they were of the same average size by the start of the breeding season. However, those compensating for low temperatures earlier in life (i.e., who then showed an accelerated growth trajectory) had reduced reproductive investment over the following two breeding seasons (males, reduced sexual ornaments and speed of building nests; females, reduced first clutch size, mean egg size, and eggs produced per year). Moreover, these deleterious effects were strongest when the perceived time available for growth compensation prior to breeding was shortest. In contrast, those fish with a decelerating growth trajectory as a result of exposure to high temperatures early in life showed an improved breeding performance compared to steadily growing controls. These results clearly demonstrate that both the shape of the growth trajectory (independent of food supply) and the time available for growth compensation have broad-reaching and prolonged effects on breeding performance, with ecological conditions that prompt catch-up growth just prior to the breeding season being especially damaging for both sexes.     

Analysis of blood chemistry and flow cytometry of gonadal cell cycle during reproductive cycle of Anabas testudineus

The population of climbing perch, Anabas testudineus, an important food fish in India, is presently under threat and has been declared endangered. A narrow range of environmental conditions for successful reproduction of the species was previously ascertained in breeding experiments. In this study, the role of physiological parameters including plasma glucose, total protein, cholesterol, and glycogen content in liver and ovary were determined with respect to the reproductive cycling stages. Flow cytometric analysis of cell cycle of ovary and testis in relation to reproductive cycle was also analyzed. In both the sexes, plasma glucose and plasma protein changed significantly during breeding cycle. Plasma cholesterol levels were reduced markedly during spawning. Liver and ovarian glycogen levels showed significant variation during reproductive cycling. Flow cytometric study revealed that the hypoploid and synthesis phase were altered significantly with breeding cycle in ovarian and testicular cells. Data indicate that the biochemical parameters indicative of the fish reproduction capacity are influenced by environmental conditions. Thus, climatic changes may therefore potentially induce biochemical alterations that may exert detrimental effects on fish reproduction and subsequent population decline.     

Somatic condition of the fish, Notopterus notopterus (Pallas) during different phases of the reproductive cycle

The study on the mathematical relationship between length and weight of fishes has considerable importance in fishery research especially for the study of fish population dynamics and patterns of growth in fish stocks. This aspect is useful in rationally managing the population of fishes, and is an index of relative robustness of the fish). Variations from expected weight or length of an individual fish or group of fish indicate the general well being and state of gonadal development. The condition of fish can be influenced by the onset of maturity. The results indicate that the overall condition of the female and male fish seems to get improved towards the approach of maturing and mature stages of the gonads during pre-spawning phases. The reduction in the condition factor (K) and somatic condition factor (Ks) during spawning phase may be because of the fish becoming exhausted due to spawning activity. Although improvement in the condition of the fish was observed on the approach of breeding period, the overall condition seems to be better in the aquatic body from which the fish was collected.     

Effects of temperature on testicular cycle of wild birds Black headed munia and Spotted munia

A long term investigation was made on the effects of temperature in the reproduction of tropical wild birds, Black headed munia, Munia malacca and Spotted munia, Lonchura punctulata. In Spotted munia delayed gonadal development as well as regression were observed in 12 degrees C treated group. In 20 degrees C treated birds the testicular volume was significantly less in the month of September and October and was significantly more in November compared to the corresponding control values. In 27 degrees C treated birds delay in testicular development was observed. In Black headed munia delayed gonadal development and regression was observed in 12 degrees C and 20 degrees C treated groups. But maximum gonadal development Delayed regression was also noticed in 20 degrees C group. In 27 degrees C treated group an inhibition of the testicular development was noticed during progressive phase (September). Present findings suggest that neither temperature nor continuous illumination could alter the circannual nature of testicular cycle in spotted munia indicating that temperature acts only as supplementary factor in the reproduction of these two bird models. We further suggest that temperature effects are mediated through changes in thyroxine levels.     

Crossing Invisible Boundaries: the Effectiveness of the Langebaan Lagoon Marine Protected Area as a Harvest Refuge for a Migratory Fish Species in South Africa

Abstract:  The application of no-take areas in fisheries remains controversial. Critics argue that many targeted species are too mobile to benefit from area protection and that no-take areas are only appropriate for resident species. The degree of protection does not depend on the size of the no-take area but rather on the time fish reside inside its boundaries during key life-history events (i.e., spawning) and during periods of peak fishing activity. We evaluated the potential of a small no-take marine protected area (MPA) inside a coastal embayment as a harvest refuge for a mobile, possibly migratory, long-lived fish species. We used acoustic telemetry to track movements of 30 transmitter-tagged white stumpnose (Rhabdosargus globiceps) across and on both sides of the boundary of a small (34 km²) no-take area over a full year. Being landlocked on 3 sides, the location of the MPA inside the lagoon made it practical to detect all boundary crossings and to calculate the time individual fish used the MPA. We detected frequent movements across the boundary, with strong seasonal and individual variations. There were significant differences in MPA use patterns between fish from different release areas. The time spent in the MPA by individual fish during summer (mean 50%; max 98%) was out of proportion with the size of that area (4% of total habitat). Summer coincided with peak recreational fishing activity and with the spawning season of this species. The small MPA provided a refuge for a part of the spawning stock of white stumpnose. Our findings suggest that if strategically placed, a small no-take area can be effective in protecting mobile species and that models of spillover from no-take areas should account for seasonal and individual variation in area use and the spatiotemporal distribution of fish and fishers.     

Does juvenile experience affect migration and spawning of adult Atlantic salmon?

Summary This paper documents differences in seasonal time of river ascent and descent, and instream behavior of adult wild and sea-ranched Atlantic salmon (Salmo salar) of the Norwegian River Imsa stock during the period 1981–1989. Wild fish use River Imsa as a nursery, and at an age of 2 years most of them migrate to the sea as smolts. The sea ranched fish are hatchery reared offspring of the River Imsa stock and are released as smolts at the mouth of the river. They are thus deprived of juvenile river life and a downstream smolt migration. Wild and sea ranched salmon feed for 1 or more years in the Norwegian Sea before homing as spawners. Both groups returned simultaneously to coastal Norway, but sea ranched fish ascended the river later and descended sooner after spawning than wild fish. All wild females and almost all wild males (96.2%) spawned in the river, whereas 13.5% and 36.7%, respectively, of the mature sea-ranched females and males left the river unspawned. The annual number, but not the proportion, of unspawned fish increased with increasing density of adult salmon in the river. Unspawned females were medium sized and small (45–70 cm); unspawned males were medium sized and large (50–90 cm). Independent of the density of spawners in the river, sea ranched fish moved up- and downstream the river more often than wild fish. More than 20% of the sea-ranched salmon and less than 1% of the wild salmon passed a trap 100 m above the river outlet more than once in each direction during the same spawning reason. Moreover, sea-ranched salmon were about twice as often seriously injured during spawning as wild fish. Lack of juvenile experience from the river may be the main reason for the behavioral differences between sea-ranched and wild fish. Offprint requests to: B. Jonsson     

Filial cannibalism and reproductive success in the maternal mouthbrooding cichlid fish Pseudocrenilabrus multicolor

Summary Pseudocrenilabrus multicolor is an iteroparous maternal mouthbrooding cichlid fish living in small and shallow waters in East Africa. It is subjected to large seasonal variations of population density. Laboratory experiments show that with increasing density and time after spawning the number of offspring present in the mouth decreased. By experimentally varying density and the numbers of fertilized and unfertilized eggs in the mouth at the end of spawning the following causes of brood size reduction were identified: (1) At high densities some of the spawned eggs are stolen by conspecifics before they are taken into the mouth. Of the eggs taken up a considerable proportion is unfertilized. (2) Unfertilized eggs are selectively swallowed from day 2 to day 5 after spawning. (3) Some of the fertilized eggs are also swallowed during mouthbrooding. (4) If the number of eggs in the mouth falls below a critical value of approximately 20% of the number of eggs spawned, they are all swallowed. By contrast, predation by conspecifics is insignificant as long as the brood is in the mother's mouth. The causes and functions of the mother's filial cannibalism are discussed.     

Flow regulation and fragmentation imperil pelagic-spawning riverine fishes.

Flow regulation and fragmentation of the world's rivers threaten the integrity of freshwater ecosystems and have resulted in the loss or decline of numerous fish species. Pelagic-spawning fishes (pelagophils) are thought to be particularly susceptible to river regulation because their early life stages (ichthyoplankton) drift until becoming free-swimming, although the extent of transport is largely unknown. Transport velocity and distance were determined for passively drifting particles, which mimicked physical properties of ichthyoplankton, in two large, regulated rivers (Rio Grande and Pecos River) of the arid Southwest United States. Particle drift data were incorporated into celerity-discharge equations (r2 > 0.90; P < 0.001), and reach-specific transport velocity was modeled as a function of discharge. Transport velocities of particles exceeded 0.7 m/s in all river reaches during typical spawning flows (i.e., reservoir releases or rainstorms) and were greatest in highly incised and narrow channel reaches. Mean transport distance of particles released in the Pecos River during sustained reservoir flows (141.1 km; 95% CI = 117.0-177.5 km) was significantly longer than during declining reservoir flows that mimicked a natural rainstorm (52.4 km; 95% CI = 48.8-56.5 km). Mean transport distance of particles in the Rio Grande during sustained reservoir flows was 138.7 km (95% CI = 131.0-147.2 km). There are 68 dams and 13 reservoirs that fragment habitats and regulate flow in the Rio Grande Basin (Rio Grande and Pecos River) in areas historically occupied by pelagophils. While the basin historically provided 4029 km of free-flowing riverine habitat, reservoir habitat now represents > 10% of the longitudinal distance. Only five unfragmented nonreservoir reaches > 100 km remain in the Rio Grande, and two remain in the Pecos River. Pelagophils were extirpated from all reservoirs and from nearly all short, fragmented reaches (< 100 km) of the Rio Grande Basin, but at least some fraction persisted in all longer reaches (> 100 km). The recovery and long-term persistence of pelagophils in regulated rivers, including those in this study, will likely depend on reestablishment and protection of long unfragmented reaches coupled with mimicry of the natural flow regime.     

Sex and reproductive aspects in Serranus cabrilla (Osteichthyes: Serranidae): macroscopic and histological approaches

The gonads of Serranus cabrilla (Linnaeus, 1758) from the Canary Islands were studied between September 1992 and July 1993. Macroscopic classification of the maturity stages was compared with histolog ical classification of gonad characteristics, and the effect␣of the classification method on the determination of the spawning season and size at maturity was investigated. Analysis of gonad organization and development confirmed that this species is synchronously hermaphroditic. Ovarian-tissue development is asynchronous, and testicular tissue consists of continuous spermatogonia. Six stages of oogenesis and five of spermatogenesis are described, based on differences in staining and in size and on differences in the nucleus and cytoplasm structure as viewed through a light microscope. Two types of atretic degeneration of eggs are also described. Agreement between macroscopic and histological staging was low, although both methods provided similar results in spawning-season determination and size at maturity. The spawning season of S. cabrilla is from February to July, with a peak in May. Fish size at first maturity (size at which 50% of all fish sampled are in relevant maturity stage) is 152 mm standard length (SL), and size at mass maturity (size at which 95% of all fish sampled are in relevant maturity stage) is 167 mm SL. Received: 21 May 1996 / Accepted: 9 August 1996     

Restoring native fish assemblages to a regulated California stream using the natural flow regime concept

We examined the response of fishes to establishment of a new flow regime in lower Putah Creek, a regulated stream in California, U.S.A. The new flow regime was designed to mimic the seasonal timing of natural increases and decreases in stream flow. We monitored fish assemblages annually at six sample sites distributed over approximately 30 km of stream for eight years before and nine years after the new flow regime was implemented. Our purpose was to determine whether more natural stream flow patterns would reestablish native fishes and reduce the abundances of alien (nonnative) fishes. At the onset of our study, native fishes were constrained to habitat immediately (<1 km) below the diversion dam, and alien species were numerically dominant at all downstream sample sites. Following implementation of the new flow regime, native fishes regained dominance across more than 20 km of lower Putah Creek. We propose that the expansion of native fishes was facilitated by creation of favorable spawning and rearing conditions (e.g., elevated springtime flows), cooler water temperatures, maintenance of lotic (flowing) conditions over the length of the creek, and displacement of alien species by naturally occurring high-discharge events. Importantly, restoration of native fishes was achieved by manipulating stream flows at biologically important times of the year and only required a small increase in the total volume of water delivered downstream (i.e., water that was not diverted for other uses) during most water years. Our results validate that natural flow regimes can be used to effectively manipulate and manage fish assemblages in regulated rivers.     

Parental care and the cost of reproduction in a Mediterranean fish

Summary Symphodus tinca is a common near-shore Mediterranean labrid fish in which females may sometimes spawn their eggs over hundreds of square meters, or alternatively spawn into well-defined algal nests. Eggs spawned in either manner are fertilized, but widely scattered eggs receive no parental care, whereas eggs spawned into nests are usually guarded by the male until they hatch. Here, I report weight changes of individual marked fish that engaged in a variety of different reproductive behaviors during three breeding seasons. Males gained weight at 0.15% per day outside the spawning season, and added 29–78% to their overall body weight between reproductive seasons, even following substantive weight losses in a spawning season (up to 20% among nesting males). Nesting and nest-guarding males lost an average of 0.32% and 0.41% of their body weight per day in 1986 and 1987. This cost is four times greater than reproduction for nonnesting males, which registered a 0.03% daily weight gain. Actively spawning females lost 0.06% of their body weight daily during the spawning season. While long-term growth rates did not appear to be substantially affected by reproduction in either sex or by parental care in males, present work does not exclude the possibility that such long-term effects may exist.