Spawning Stage Research Articles

Some aspects of the reproductive biology of the twaite shad, Alosa fallax (Lacépède, 1803), in the River Ulla (Northwest of the Iberian Peninsula)

Some aspects of the reproductive biology of the twaite shad, Alosa fallax (Lacépède, 1803), in the River Ulla (Northwest of the Iberian Peninsula)

Fatty acids in female’s gonads of the Red Sea fish Rhabdosargus sarba during the spawning season

Objective: To determine the fatty acids profiles in female fish, Rhabdosargus sarba (R. sarba) from the Red Sea during the spawning season. Methods: Monthly individual R. sarba were obtained from Bangalah market in Jeddah, Red Sea and transported to the laboratory in ice aquarium. The total length, standard length and weight were measured, fishes were dissected. Ovaries were removed, weighed and 10 mL of concentrated hydrochloric acid were added to 10 g of the ovary in a conical flask and immersed in boiling water until the sample was dissolved and the fat was seen to collect on the surface. The conical was cooled and the fat was extracted by shaking with 30 mL of diethyl ether. The extract was bowled after allowing the layers to separate into a weighed flask. The extraction was repeated three times more and distilled off the solvent then the fat dried at 100 °C, cooled and weighed. Then 50 mg of lipid was put in a tube, 5 mL of methanolic sulphuric acid was added and 2 mL of benzene, the tube well closed and placed in water bath at 90 °C for an hour and a half. After cooling, 8 mL water and 5 mL petroleum were added and shaked strongly and the ethereal layer was separated in a dry tube, evaporated to dryness. The fatty acid methyl esters were analyzed by using a Hewlett Packard (HP 6890) chromatography, a split/splitless injector and flame ionization detector. Results: In female R. sarba, a total of 29 fatty acids were detected in ovaries throughout the spawning season. The main fatty acid group in total lipid was saturated fatty acid (SFA, 28.9%), followed by 23.5% of polyunsaturated fatty acids (PUFA) and 12.9% of monounsaturated fatty acids (MUFA). The dominant SFA were palmitic and stearic, the major MUFA were palmitoleic and oleic, and the major PUFA were C18:2 and C22:2. During spawning stages, there were no significant differences in total SFA, MUFA and PUFA. The highest value of SFA was in late spawning (36.78%). However, the highest value of MUFA and PUFA was in spawning (16.70% and 24.96% respectively). During spawning season there were significant differences in total SFA between March (late spawning stage) and December (nearly ripe stage), P<0.05. Conclusions: From the present study it has been shown that 29 fatty acids were detected in ovaries of R. sarba throughout the spawning season. The main fatty acid group in total lipid was SFA followed by PUFA and MUFA. The dominant SFA were palmitic and stearic, the major MUFA were palmitoleic and oleic, and the major PUFA were C18:2 and C22:2. The highest value of SFA was in late spawning. However, the highest value of MUFA and PUFA was in spawning.

Efecto del fotoperiodo y la temperatura sobre la composicion bioquimica en reproductores silvestres de cabrilla sardinera, Mycteroperca rosacea (Streets, 1877)

Condition factor ( K ), gonadosomatic index, ( IGS ), hepatosomatic index ( IHS ) and fat visceral index ( IGV ) were estimated and the biochemical composition in different tissues of wild leopard grouper broodstock was determinate too, in order to evaluate them along a reproductive cycle and see the relationship of these changes with respect to the water temperature and photoperiod in the sampling area. 187 brooders were caught, 146 females and 41 males in the Gulf of California, Mexico. Significant differences ( P < 0.005) in the IGS , IHS and IGV but not for K were observed. Significant changes ( P < 0.05) were also observed in most of the biochemical parameters, being the highest value during the spawning stage, whereas the lowest occurred during the resting stage. Significant correlations ( P < 0.05) between all estimated indices and biochemical parameters were observed, while only significant correlations ( P < 0.05) between the IGS and IGV with respect to water temperature.

Diel Reproductive Periodicity of Haddock in the Southwestern Gulf of Maine

AbstractWe studied a population of Haddock Melanogrammus aeglefinus in the Gulf of Maine to determine whether it exhibits diel spawning periodicity. Commercial fishing vessels were chartered for 25 dedicated long‐lining trips to collect sexually mature Haddock in the Stellwagen Bank National Marine Sanctuary at locations identified by commercial fishers as having spawning aggregations. In order to examine diel effects on Haddock reproduction, the changes in CPUE and percentages of male and female Haddock of all reproductive maturity stages, as well as gonadosomatic index (GSI), were observed across a 24‐h diel cycle. The comparison of diel patterns among different maturation stages was used to differentiate diel periodicity due to spawning from feeding behavior. Diel periodicity was observed for the proportion of males and females in the catch, the proportion and CPUE of male and female maturation stages most indicative of imminent spawning, and for female GSI. Although spawning occurred throughout the diel cycle, peak spawning of females occurred during the evening hours (1700–2100 hours) and gradually declined to low values during the day at 0900 hours. In an apparent contradiction male spawning stages were uniformly high except for lows during the night between 2100 and 0100 hours. We hypothesize that this pattern is consistent with lekking behavior where strong competition among spawning‐ready males during courtship would reduce their feeding activity during the peak spawning hours. Strong annual differences in diel periodicity may have resulted from different temporal patterns in the spawning season or density dependence, or both.

한국 진해만 해역에 분포하는 개조개, Saxidomus purpuratus의 재생산 연구 : 산란 및 군성숙각장

This study investigated purplish Washington clam, Saxidomus purpuratus on its gonadal development, reproductive cycle and shell length (age) at 50% female group maturity from January to December 2011 in Jinhae Bay, Korea. This species is dioecious. The gonad index (GI) began to increase in January, reached the maximum value in May and to decrease in June, reached the minimum value in September then to increase slowly in October again. The reproductive cycle of the clams can be divided into five successive stages: the early active stage (Ea, from February to March), the late active stage (La, from January to March and October to December), the ripe stage (R, from January to May), the spawning stage (S, from June to December) and the degenerative and inactive stage (Ia, from January to February and November to December). The spawning periods were from June to December and the main spawning periods were from July to October. The shell length at 50% female group maturity (SL50) was estimated to be 63.6 mm, which can be converted as sexual maturity age of 2.2 year.

Analysis of germ cell proliferation, apoptosis, and androgenesis in the Lake Van fish (Chalcalburnus tarichi) during testicular development

In the present study, the testis histology, gonadosomatic index (GSI), germ cell proliferation and apoptosis, and the plasma 11-ketotestosterone (11-KT) and testosterone (T) levels of male Chalcalburnus tarichi were analyzed. According to the histological examinations of the specimens that were caught between February 2009 and January 2010, three testicular stages were determined. Those stages were as follows: (1) recrudescence or prespawning (July-April), (2) spawning (May-June), and (3) postspawning (July). It was observed that the GSI increased gradually, starting from the recrudescence stage, and it reached peak values at the spawning stage, while the lowest values were in the postspawning. Germ cell proliferation in the testis was detected using a proliferating cell nuclear antigen (PCNA), and germ cell apoptosis was detected by transferase dUTP nick end labeling staining. The germ cell PCNA and apoptosis index values were calculated. It was indicated that germ cell proliferation was observed in all of the testicular stages. The highest germ cell PCNA index (PI) levels were detected in July, August, and September, which then dropped in October and stabilized between February and April. The lowest PI values were detected in the spawning stage (May-June). Germ cell apoptosis was observed in all of the months, and the highest apoptotic index values were detected in August, September, October, May, and June. Plasma 11-KT and T levels were at their highest levels in May and June, and it was detected as stabile in the other months. There was a correlation between GSI, PI, and plasma androgen levels. In conclusion, the present data illustrate testicular development stages for C. tarichi and show changes in the level of GSI and sex steroid biosynthesis through spermatogenesis.

Environmental and hormonal control of induced spawning in thin-lipped grey mullet, Liza ramada (Risso)

Introduction The reproductive cycle can be controlled by either placing the fish in an appropriate environment or by changing the internal regulating factors of the fish with injected hormones or other substances. Aim of the study The present work was designed to determine the suitable environmental and hormonal requirements for induced spawning of thin-lipped grey mullet, reared in freshwater fish farms. Materials and methods The application of a high-potency synthetic analogue of luteinizing hormone-releasing hormone agonists (LHRH-a) and human chorionic gonadotropin (HCG) for inducing the final stages of maturation, ovulation, and spawning in mullets was investigated in ripe spawners, reared in freshwater fish farms, with average egg diameters of 0.600 mm or more, in suitable water temperature and salinity. Results Two hormonal injection strategies were used. The first involved the use of HCG as a priming injection, followed, 24 h later, by a resolving injection of HCG. The second strategy followed the same time frame but the priming injection was HCG and the resolving injection was luteinizing hormone-releasing hormone agonists alone or in combination with HCG. The use of pregnyl (HCG) as a priming injection at a dose of 20 000 IU/kg body weight, followed by a second injection of 40 000 IU HCG/kg body weight 24 h later proved to be effective in inducing final oocyte maturation, ovulation, and spawning in Liza ramada at 44–50 h after hormonal injection. The optimum water temperature and salinity was 19oC and 35%, respectively. Translucent ovulated eggs had coalesced lipid and yolk masses. The fertilized eggs had one or more oil globules gathered in the upper space of the egg. The blastodisc was situated on the bottom side of the floating egg. Conclusion HCG is very useful for inducing and synchronizing spawning in L. ramada ripe spawners, reared in freshwater fish farms, in combination with suitable environmental factors.

Pertumbuhan Jaringan Stipe dari Jamur Sagu (Volvariella sp) Endemik Papua dalam Kultur in vitro

Sago mushrooms are edible fungus which it grew naturally on decaying sago pith. The objectives of the research were defined an appropriate formulation medium for growth and development of stipe tissue of sago mushroom in order to result spawn stages. The parent of the tissues used as explants were selected from the best performance of sago mushroom which grew naturally. The research divided into three experiments: 1) Initiation of growth hyphae from stipe tissue; 2) hyphae proliferation; and 3) spawn formation. Murashige and Skoog (MS) and Knudson-C (KN) medium enriched 15 and 30% coconut water are the best medium for growth initiation and proliferation of hyphae. Both of these medium induced the explant grew rapidly and resulted vigorous hyphae. No different effect among concentration treatment of coconut water was observed for initiation and proliferation hyphae. The fact that all of the formulation medium used for spawn formation were able to induce spawn development become spawn stage. Even so, the best mediums for spawn formation were medium formulation 9 and 10.

실내 사육한 줄가자미(Clidoderma asperrimum)의 성 성숙과 생식주기

The gonadosomatic index (GSI), sex steroid hormones and gonadal development of roughscale sole Clidoderma asperrimum cultured in indoor tank were investigated to evaluate its sexual maturation and reproductive cycle. The highest GSI values of female and male were <TEX>$6.91{\pm}4.03$</TEX> (May) and <TEX>$0.16{\pm}0.08$</TEX> (August), respectively. The reproductive cycle would be classified into four successive developmental stages: growing stage (December to February), maturation stage (March to April), ripe and spawning stage (May to June), recovery and resting stage (July to November). The highest plasma testosterone (T) and estradiol-<TEX>$17{\beta}$</TEX> (<TEX>$E_2$</TEX>) levels of female were <TEX>$259.4{\pm}76.8$</TEX> and <TEX>$633.3{\pm}182.5$</TEX> pg/mL, respectively in May. Also <TEX>$17{\alpha}$</TEX>, <TEX>$20{\beta}$</TEX>-dihydroxy-4-pregen-3-one (<TEX>$17{\alpha}$</TEX>, <TEX>$20{\beta}$</TEX>-OHP) levels of female peaked in April before spawning season (<TEX>$244.2{\pm}42.5$</TEX> pg/mL). The highest plasma testosterone (T) and 11-ketotestosterone levels of male were <TEX>$231.0{\pm}46.0$</TEX> and <TEX>$273.9{\pm}54.5$</TEX> pg/mL, respectively in April. But there was no significant difference in <TEX>$17{\alpha}$</TEX>, <TEX>$20{\beta}$</TEX>-OHP.

Gonadal cycle of the dwarf oyster Ostreola stentina from the south of the Gulf of Hammamet on the eastern coast of Tunisia

The reproductive cycle of the dwarf oyster Ostreola stentina (Payraudeau 1826) at Monastir in the south of the Gulf of Hammamet on the east coast of Tunisia was studied using condition indices and histological techniques. The species was shown to be a protandric hermaphrodite. Whereas males dominated the small shell length categories (12.45–34.99 mm), females (21.00–47.16 mm) and hermaphroditic individuals (30.00–57.95 mm) become more predominant with increasing size, suggesting that individuals may undergo protandric development. The overall male to female ratio was 1.0:1.7. Gametogenic development begins in February–March for females and in September for males, and spawning occurs during April and July for females and December and July for males. There was a clear relationship between the gonadal condition index and gametogenic stage for both sexes. Values increased from zero in their early stage of development and peaked during ripe and spawning stages, before decreasing in the spent stage. However, the meat condition index did not show any statistical differences between gametogenic stages.

Storage and reproductive strategy of the carpet-shell clam, Ruditapes decussatus in the Gulf of Gabès (Tunisia)

In this study, the variations of glycogen concentrations in Ruditapes decussatus from Sfax coasts (Tunisia) were described in relation to the reproductive cycle. Separate analyses were made of gonad, adductor muscle and ‘remainder’. The timing of gametogenic development and spawning was evaluated using qualitative histology associated with image analysis including (1) the estimation of the gonadal occupation index (GOI), (2) surface area occupied by reserve tissues and (3) variation in oocyte diameter. The reproductive cycle of R. decussatus exhibited partial asynchronization between sexes, the major difference being observed in the duration of the spawning period. Contrary to previous studies, we observed continuous partial spawning (e.g. 50% of ripe oocytes still subsisted at the partial spawning stage). During the gametogenic cycle, GOI varied significantly in males and in females. Most oocytes were ripe and ready to spawn when their diameter reached or exceeded 45 µm. The expansion of gonad was inversely proportional to the development of the foot tissue. Glycogen concentration showed significant temporal variations between tissues, indicating the clear differentiation in energy storage between the clam organs.

The sources and metabolic dynamics of Schistosoma japonicum DNA in serum of the host

The polymerase chain reaction (PCR) assay has turned out to be one of the most potential tools for diagnosis of schistosomiasis. However, the source and metabolic dynamics of Schistosoma japonicum DNA in the blood of hosts is not clear. In this study, rabbit models with monosexual and mixed sexual cercariae infection were established to interpret the source of the parasite DNA in serum of the hosts. Following administration of praziquantel at 7weeks postinfection, the metabolic mechanism of S. japonicum DNA in serum of the hosts was studied. The findings showed that, for the monosexual cercariae infection, the parasite DNA was detectable in serum of the host from day 3 to week 3 postinfection, while for the mixed sexual cercariae infection, the detection results were continually positive during the 7weeks after infection. After treatment with praziquantel, detection of S. japonicum DNA in rabbit sera became positive at the second day posttreatment, and the positive period lasted 3weeks in the monosexual cercariae infection group. However, with the mixed sexual cercariae infection group, the PCR results remained positive for 16weeks after treatment. We conclude that the S. japonicum DNA in host serum primarily comes from the residual body of dead schistosomula and/or tegument shedding of worm growing in the first 4weeks postinfection, while during the spawning stage of the female schistosome, the parasite DNA mainly comes from the disintegration of inactive eggs. The duration from treatment to total elimination of worm origin DNA in serum is not exceeding 3weeks. However, the DNA release from inactive eggs can last for more than 16weeks. Further studies are needed to address the sources and metabolic dynamics of S. japonicum DNA in human serum.

Annual reproductive cycle, spawning periodicity and sexual maturity of blue runnerCaranx crysos(Pisces, Carangidae) from the Gulf of Gabes (Tunisia, Eastern Mediterranean)

Summary From June 2004 to May 2006, the reproductive biology of the blue runner Caranx crysos was studied in the Gulf of Gabes (Southern Tunisia). Of 1668 individuals examined, 777 were females (46.6%) and 891 were males (53.4%). The sex ratio significantly deviated in favour of males (♀:♂ = 0.87 : 1). The difference in the numbers of females and males was significant among size-classes. However, there was no significant difference between sexes over months and seasons. Monthly changes in the Gonado-Somatic Index (GSI) showed a rapid increase during summer to very high levels in July (3.51% for males and 2.55% for females) and August (3.47% for males and 2.59% for females) before declining sharply in September (0.58% for females and 0.38% for males). The gametogenesis activity began with a pre-maturation phase, from 20 May to the first 10 days of July, followed by a pre-spawning phase, from 20 July to 20 August. From the last 10 days of August to 20 September the gonads were in the ripe and spawning stages. From the end of September to early May, gonads were in the post-spawning and resting stages. The size at which 50% of the population reached sexual maturity was significantly different in males and females: males attained sexual maturity at fork length FL50 = 210.20, whereas females attained maturity at FL50 = 222.3 mm. Age at maturity was 2.4 years for males and 2.8 years for females.

Sexual Difference in the Migration Pattern of Blue Marlin, Makaira nigricans, Related to Spawning and Feeding Activities in the Western and Central North Pacific Ocean

The reproductive condition and stomach contents of blue marlin, Makaira nigricans Lacepede, 1802 (n = 645), were quantitatively investigated in three different regions of the North Pacific Ocean between 2003 and 2009. Males strongly dominated (females:males = 34:439) in Region III (4°N-21°N, 131°E-154°W) throughout the year, and eight females (28%) had ovaries in the maturing or spawning stage. Although the sampling months were limited to September-November in Region II (18°N-32°N, 171°W-140°W), the sex ratio was more similar (females:males = 28:26) and there was no evidence of spawning. Only females (n = 100) were observed in Region I (33°N-36°N, 135°E-140°E) from July to September, the main season when blue marlin occur off the coast of Japan, and no females had ovaries in the maturing or spawning stage. Stomach-content analysis revealed that the feeding intensity of females was higher in Region I than in the other two regions. These results suggest that blue marlin prey items may be more abundant at non- spawning areas in Region I, to which female blue marlin migrate for feeding. In contrast, lower feeding intensities and evidence of spawning in Region III suggest that blue marlin prey may be scarce in spawning areas. Male blue marlin tend to remain and wait for females in spawning areas, forgoing a feeding migration.

Attenuated reproduction of Strombus gigas by an Apicomplexa: Emeriidae-like parasite in the digestive gland

An intense and generalized sporozoan infection was detected in every population of the queen conch, Strombus gigas through the Caribbean. In this contribution we establish the relationship between occurrences of an Apicomplexa: Emeriidae-like organism and reproductive activity at San Andres archipelago, Colombia. Occurrence of the parasites was estimated counting the feeding stage Merozoites and cysts Sporozoites at 40× magnification. Nonmetric multidimensional scaling analysis (NMDS) was made to correlate the parasites stages abundance with frequency of the reproductive stages. Gametogenesis and spawning were always low coinciding with high numbers of Merozoites, a positive correlation was established between parasite abundance with reabsorption and undifferentiated stages, and negative correlation was observed between parasite abundance with maturity and spawning stages. The nonmetric multidimensional scaling (NMDS) shows that gametogenesis, maturity and spawning increase as the number of parasites decrease, factor that could be threatening reproduction of S. gigas through the Caribbean.

In vitro biomonitoring of contamination by estrogenic compounds in coastal environments: Comments on the use of M. galloprovincialis

The use of mussel extracts in in vitro bioassays which express the estrogen receptor could provide valuable information on the bioavailability of endocrine disruptors in coastal environments. The aim of this study was to assess the temporal variability of the estrogenic responses in bioassays in Mytilus galloprovincialis. A 6-month in situ experiment was conducted in order to follow the estrogenic activity on MELN cell line during the reproduction stages of mussels. Estradiol equivalents (EEQ) determined in mussels using the MELN cell lines ranged from 0.79 to 3.72 ng/g dry weight (d.w.) in males, from 0.42 to 2.33 ng/g d.w. in females and from 3.41 to 4.2 d.w. in undifferentiated bivalves. We observed an increase in EEQ values during the spawning stage for males, not for female. The maximal EEQ values were observed at the indifferent stage. We discuss these results in regards to the actual knowledge on mussels' reproductive cycle and to the possible impact of xeno-estrogens. Variations of E2 levels in mussels must be taken into account for further studies on xeno-estrogens monitoring using hER reporter cell-lines bioassays.

Breeding and Larval Rearing of Asian Catfish, Clarias batrachus (Linnaeus, 1758) on Live and Artificial Feed

A study was conducted to observe the breeding and larval rearing of Asian Catfish, Clarias batrachus fed with live and/or artificial feed for 21 days in an indoor hatchery. The brooders of C. batrachus (Av. wt of female 160 ± 10.5 g; Av. wt of male 120 ± 6.75 g) were procured from outside ponds and stocked in a pond near the experiment site 2-months prior to spawning. The fishes were successfully induced bred using ovaprim @ 1.0–2.0 ml/kg body weight (bw) to females and 0.5–1.0 ml/kg bw to males. Fertilization, hatching and survival percentages at spawn stage were respectively recorded 70.6 - 72.8, 60.7 - 55.3 and 54.3 - 56.2. After yolk-sac absorption, fry of three age groups 7, 14 and 21 days were subjected to feed trial using Artemia nauplii followed by laboratory made feed for 21 days. Weekly sampling indicated that higher age groups constantly maintained higher lengths and weights with highest survival in the age group of 14-days old fry and SGR in 7-days old. The quality of hatchery water was recorded for temperature 29 ± 1°C, pH 7.2 ± 0.2, DO 7.1 ± 0.3 mgL-1 and total alkalinity 132 ± 4.0 mgL-1 respectively.

A life cycle approach to modeling sea lamprey population dynamics in the Lake Champlain basin to evaluate alternative control strategies

Sea lamprey (Petromyzon marinus) is a nuisance species in the Laurentian Great Lakes and Lake Champlain that has devastated native fish populations and hampered sport fisheries development. We developed a modified stage-based life history matrix for sea lamprey to analyze the effects of various management efforts to suppress sea lamprey population growth in Lake Champlain. These efforts targeted different life stages of the sea lamprey life cycle. A beta distribution was used to distribute stochastic larval populations among twenty sea lamprey-bearing tributaries and five deltas to Lake Champlain, from which sea lamprey that survive through larval metamorphosis were then pooled into a lake-wide parasitic-phase population. Parasitic-phase survival to the spawning stage was evaluated based on proximity to the natal tributary and on the size of the resident larval population in each tributary. Potential control strategies were modeled at egg to emergence, larval, and spawning stages to reduce vital rates at each stage, with the goal of suppressing parasitic-phase production. Simulations indicate that control of the larval stage was essential to achieving this goal, and with supplemental effort to reduce the vital rates at early life stages and at the spawning stage, the parasitic-phase population can be further suppressed. Sensitivity simulations indicate that the life history model was sensitive to egg deposition rate, abundance of parasitic-phase sea lamprey from unknown, uncontrolled sources, and the method in which parasitic-phase sea lamprey select tributaries for spawning. Results from this model can guide management agencies to optimize future management programs.

Gametes and embryos of sea urchins (Paracentrotus lividus, Lmk., 1816) reared in confined conditions: their use in toxicity bioassays

Sea urchins of the species Paracentrotus lividus, collected along the Southern Adriatic coast at the end of their reproductive season, were reared in a recirculating aquarium under controlled temperature and feeding conditions in order to induce off-season maturation of gametes to be used in toxicity bioassays. After 14 weeks of rearing, the gonad index was calculated, histological analyses of the gonads were performed, their fertilisation ability was measured and the EC50 for copper in embryotoxicity bioassays was evaluated. The sperm motility pattern (based on the percentages of total motile and rapid sperm, together with sperm velocity parameters) was assessed using a computerised analyser. All specimens showed a significant increase in gonad yield with respect to field-collected animals and were in pre-spawning or spawning stages. The motility parameters, fertilisation ability and EC50 level of the collected gametes were comparable to those of field-matured specimens. In conclusion, the sea urchins reared under experimental conditions were characterised by faster gonad maturation than the field population, producing viable gametes and larvae whose biological response in toxicity bioassays was similar to that of field-reared specimens of P. lividus.

Bathymetric segregation of spawning stages in the Atlantic sardine Sardina pilchardus

The present study analyzed the spatio-temporal pattern of spawning aggregations of the Atlantic sardine Sardina pilchardus using a large set of reproductive data derived from 5 daily egg production method (DEPM) surveys conducted off Portugal and the Gulf of Cadiz. Similar to previous results for the Mediterranean sardine, sardines in the Atlantic were shown to form ephemeral spawning aggregations in which actively spawning females separated spatially from the remaining population, taking with them a large proportion of males. These aggregations were shown to take place at depth; specifically, bathymetric positioning of reproductively active individuals changed during the spawning cycle in such a way that imminent spawners were located at greater depths compared to recent spawners or non-spawning females. This pattern of bathymetric segregation of sardine spawning stages is in agreement with previously published evidence that sardines spawn at depth, either from indirect acoustic sampling data or from the occurrence of early embryonic stages at greater depths. A number of physiological mechanisms that may explain changes in the bathy metric positioning of actively spawning individuals are also suggested.