Effects of Phase-Shifted Photoperiod Regimes on Oocyte Growth and Hormonal Profiles in Female Striped Bass Morone saxatilis

Abstract.— The use of 12–mo long, but phase-shifted advanced and delayed photoperiod cycles in the regulation of the reproductive cycle was investigated in captive-reared female striped bass Morone saxatilis during the 3-yr study in an attempt to control the timing of sexual maturation under simulated photoperiod conditions. Phase-shifted photoperiod cycles did not induce a full shift in oogenesis during the first year cycles, but did in the following years. Spawning time, indicated by maximum oocyte diameters, was advanced up to 4 mo in females maintained under the phase-shifted advanced photoperiod, and delayed up to 4 mo when they exposed to the phase-shifted delayed photoperiod, compared to the natural spawning time in Spring (March-May). Phase-shifted photoperiod regimes shifted the profiles of plasma testosterone (T) and estradiol (E₂), corresponding to the shift of oogenesis in the respective groups. Significant increases in T and E₂ levels occurred during the vitellogenic phase, and these levels peaked before the occurrence of maximum oocyte diameters. The studies demonstrate that phase-shifted photoperiod regimes can be used to control oogenesis, and have implications for ensuring the year-round supply of mature female striped bass, particularly in domesticated striped bass.     

The Annual Reproductive Cycle of the White Bass Morone chrysops

The gametogenic cycle of the white bass Moronc chrysops was characterized for one year at monthly intervals by measuring circulating levels of the sex steroid hormones testosterone (T) and 11-ketotestosterone (11-KT) in males, and 17β-estradiol (E₂) and T in females. Vitellogenin (VTG), the egg yolk precursor, was also measured in female blood plasma. Gonadal status of individual fish was assessed by histological evaluation, measurement of oocyte diameters, and spermintion response. At the onset of vitellogenesis (October), blood plasma levels of E₂ and T were low, but increased significantly as the spawning period (March-April) approached and oocytes attnined their maximum diameter. All stages of oocyte development were observed in mature females, indicating that the white bass is a multiple-clutch, groupsynchronous spawner. Androgen levels increased in males throughout the reproductive cycle and reached maximal levels during the spawning period. The increase in androgens coincided with sperm production and spermintion in males. The circannual endocrine and gonadal development patterns observed in white bass were similar to those of other members of genus Moronc .     

Reproduction of striped bass, Morone saxatilis (Walbaum), broodstock: monitoring maturation and hormonal induction of spawning

Abstract Levels of gonadal steroid hormones were quantified in an adult striped bass, Morone saxatilis (Walbaum), broodstock during their gametogenic cycle. Blood plasma concentrations of Estradiol (E₂) and testosterone in females, or 11-ketotestosterone(11-KT) and testosterone (T) in males, were used as indicators of maturation. In both sexes, hormone levels were low in summer but increased significantly by late October to intermediate levels which were then maintained until late January. They then increased again rapidly to maximum pre-spawning values attained in late February or March, and subsequently decreased during the spawning period (April and May) with an increased incidence of spent fish with low hormone levels. The changes in blood hormone concentrations coincided with annual changes in photoperiod and water temperature that may be useful landmarks for maturation in captive broodstock. Mature females were implanted with pellets containing a dose of approximately 20 μg/kg body weight of [D-Ala⁶-Pro⁹-Net]-LHRH (GnRHa) in a matrix of cholesterol (CH) and cellulose. In April, they had not yet begun final oocyte maturation (FOM) and were too immature for conventional induction of spawning by injection with human chorionic gonadotropin (hCG). In early April, females given two 95% CH (slow hormone-release) GnRHa pellets (95/95) or females given one 80% CH (fast hormone-release) GnRHa pellet and one 95% CH GnRHa pellet (80/95) spawned within 13 days treatment (n= 4) with good egg fertility (76 ± 7% of total) and hatch rates (62 ± 15% of fertile). Females given dual fast-release GnRHa pellets (80/80) or control (Sham) pellets did not spawn or show evidence of increased oocyte diameter or development. In late April, four of six females given the 80/95 GnRHa pellet combination spawned within 9 days. Three fish produced fertile eggs (54 ± 18%). one spawned overripe eggs, and the remaining two increased oocyte diameter and maturation. Three corresponding controls did not spawn, and two of these showed clear signs of atresia within 11 days. In early May, some females were undergoing early FOM and were mature enough to be spawned by hCG injection. Three were given a single 80% CH GnRHa pellet and spawned within 6 days of treatment to produce fertile eggs (44 ± 6%). Of two other females given dual 80% CH GnRHa pellets, one spawned infertile eggs and the other failed to spawn within 9 days. GnRHa implants show promise as a technique for inducing spawning of captive striped bass broodstock although the optimum hormone delivery systems, dosages and release rates should be verified for fish at specific maturational stages.     

Oocyte Diameter and Plasma Vitellogenin as Predictive Factors to Identify Potential Channel Catfish,Ictalurus punctatus,Suitable for Induced Spawning

This study monitors the progression of oocyte size and plasma hormone profiles of female channel catfish, Ictalurus punctatus, at monthly intervals to stage expectant ovulating, females for strip spawning. The “critical minimum” diameter of an oocyte to reach threshold maturity for channel catfish was 2.5 ± 0.21 mm. Monthly increases of oocyte diameters and plasma vitellogenin concentrations were linear until spawning. The reproductive performance of cannulated and noncannulated catfish did not differ, negating adverse effects of routine cannulation. This study suggests oocyte diameter in channel catfish can be used as a predictive factor to determine and stage potential broodfish suitable for hormone‐induced spawning.     

Induced Final Maturation and Spawning of the Marbled Grouper Epinephelus microdon Captured from Spawning Aggregations in the Republic of Palau, Micronesia

A high percentage (98.3%, N = 60) of the marbled grouper Epinephelus microdon individuals captured from spawning aggregations during July and August 1993 in the waters surrounding the island of Koror, Republic of Palau, Micronesia, were in the stage of maturity at which final maturation and spawning could be hormonally induced. The sex ratio of the captured fish was highly skewed towards males (4 male:1 female). Sexually immature females comprised the smallest size class, (<0.6 kg body weight (BW) or 33.0 cm total length (TL)), while sexually mature females were restricted to the 0.6–1.5 kg BW (33.0–46.4 cm TL) groups. Males predominated in size classes >0.6 kg BW, and individuals >1.5 kg BW (46.4 cm TL) were exclusively male. All females with oocytes that averaged ( N = 50) >400 μm in diameter were successfully induced to spawn by a two-injection protocol using human chorionic gonadotropin (HCG) at total dosages of 2,100–3,200 IU/kg fish. All males used in the spawning trials were administered a single injection of HCG at dosages of 500 or 1,000 IU/kg fish. Fecundity ranged between 7.96 × 10⁵−1.24 × 10⁶kg BW, average spawned egg diameters ranged between 769–832 μm, percent fertilization ranged between 32.6%–99.9%, and hatching percentages were >90.0%. Total fat content of eggs obtained from a pooled spawning event was 14.1 mg/100 mg dry weight. The data indicate that HCG is a suitable treatment for the induction of spawning in marbled grouper females that possess a mean oocyte diameter of 400 μm or greater.     

Effects of Maternal Age on Fecundity,Spawning Interval,and Egg Quality of Nile tilapia,Oreochromis niloticus (L.)

Effects of maternal age on fecundity, spawning interval, and egg quality of Nile tilapia, Oreochromis niloticus (L.), was examined for four age groups (4, 9, 16, and 24 mo) in circular concrete tanks in a recirculating system. Fecundity (eggs per spawn), weight (g), and egg quality were monitored every 4 d for the 168‐d experimental period. Eggs per spawn correlated with maternal age, while it did not correlate with body weight. Eggs per spawn increased by twofold between 4‐ and 24‐mo‐old females, while eggs per female per d did not differ. Implying that eggs per female per d was influenced by spawn per female as well. Eggs per female per d was 1.8 and 2.4 times higher in 9‐mo‐old females than 16‐ and 24‐mo‐old females, respectively. Eggs per female per d showed a decline concurrent with per spawn per female trend after 18‐mo old. Four‐mo‐old females produced eggs that were more uniform in size and weight than others. While egg size (mm) and weight (mg), and their variations within eggs per spawn increased, percent fertilization and hatchability decreased with age of females. Biological optimum age range for reproducible production of good quality eggs was 6–18 mo. This could be adopted in selecting breeders for better seed production.     

Volitional Spawning of Black Sea Bass Centropristis striata Induced with Pelleted Luteinizing Hormone Releasing Hormone-Analogue

The black sea bass is a high‐value marine serranid and is a prime candidate for intensive cultivation. Reliable methods for controlled spawning are needed to accelerate the development of hatchery technologies that result in mass production of healthy juveniles. During 1998–2001, spawning studies were conducted at The University of North Carolina at Wilmington (UNCW) and at the South Carolina Department of Natural Resources (SCDNR), Charleston, using pelleted luteinizing hormone releasing hormone analogue (LHRH‐a). From April through July 2001, 28 vitellogenic‐stage females, with mean oocyte diameters (MOD) ranging from 277–448 μm, were implanted with a 95% cholesterol‐5% cellulose pellet containing LHRH‐a (‐50 μg/kg body wt) at UNCW. In 10 individual spawning trials, females with MOD of 305–448 μm and maximum oocyte diameter × 475 μm spawned volitionally beginning 2–3 d post‐implantation (PI) and continued spawning over an average of 1.9 d (range = 1–4 d). Individual females released a mean total of 149,000 eggs (117,000 eggs/kg) with a mean buoyancy rate of 40.5% (floaters). Fertilization and hatching rates were 98% and 27.2% of floaters, respectively, yielding 14,600 yolksac larvae/female (12,600 yolksac larvae/kg body wt), and overall egg viability averaged 8.9%. In eight group spawning trials (2–3 females/group), average performance of females, including fecundity (103,800 eggs/female; 105,500 eggs/kg body wt), buoyancy rate (42.5%), fertilization and hatching rates (97.7% and 24.3% of floaters), numbers of yolksac larvae produced (10,900 yolksac larvae/female; 10,100 yolksac larvae/kg body wt), and overall egg viability (10.6%) was comparable to what was seen in individual spawning trials. From 1998–2000, a total of 58 vitellogenic stage (70% of oocytes 500 pm) females were implanted with pelleted LHRH‐a (‐50 μg/kg body wt) in nine group spawning trials (2–19 females/group) at SCDNR. Volitional spawning typically began 18–42 h PI and recurred every 1–3 d for an average duration of 9 d. Female groups released a mean of 560,000 eggs (84,000/female; 132,000/kg body wt) over the spawning period, with mean buoyancy rate of 25.7% floaters. Fertilization and hatching rates were 17.7% and 11.6 % of floaters, respectively, yielding 4,300 yolksac larvae/female (4,600 yolksac larvae/kg body wt). Overall egg viability was 2.9%. Captive wild‐caught black sea bass were induced to undergo repetitive volitional spawning by implantation of pelleted‐LHRH‐a, consistent with a multiple clutch group synchronous pattern of ovarian development. Group spawning appears to be a practical way to compensate for variable fecundity and egg viability of individual females. Research is needed to identify optimum hormone treatments and eligibility requirements.     

Annual cycle of plasma lipids in captive reared striped bass: effects of environmental conditions and reproductive cycle

Protein, lipid and fatty acid concentrations in plasma of eight male and eight female six year old captive striped bass (Morone saxatilis) were monitored monthly over the course of two reproductive cycles as part of an effort to investigate the time course of lipid class mobilization and subsequent deposition in gonads. Total protein levels (44.2 ± 0.67 mg ml^–1, range 20.6–86.4) showed seasonal fluctuation, but did not vary with sex. Total lipid concentrations in the plasma of both males (17.7 ± 0.61 mg ml^–1) and females (14.1 ± 0.64 mg ml^–1) showed seasonal fluctuations with the lowest levels in late Spring during spawning. Plasma lipids in females were significantly (p < 0.0001) lower than those of the males except during early ovarian secondary growth. Analysis of the lipid class composition revealed that the decrease in plasma lipid concentrations in females prior to spawning is primarily due to a decrease of up to 50% in the phospholipid content of the plasma relative to males. Striped bass vitellogenin was found to contain approximately 20% lipid by weight with nearly 80% of the lipid being phosphatidyl choline (PC). Vitellogenin levels previously measured in these individuals were highest during the winter months and decreased in the 2 months prior to spawning. Although mature striped bass oocytes are rich in wax esters, no wax esters or fatty alcohols were found in the plasma. Analysis of the fatty acyl composition of separated lipid classes suggests that PC is the primary carrier of the essential (n=3) fatty acids 22:6 (DHA) and 20:5 (EPA) to the gonads. Fatty acid analysis of the lipids associated with vitellogenin revealed that levels of essential fatty acids were low relative to vitellogenin-borne lipids from other teleosts. The lack of detectable wax esters in plasma lipids of female striped bass suggests that these abundant lipids in mature eggs are synthesized within the oocytes.     

Progress Toward Year-round Spawning of Southern Flounder Broodstock by Manipulation of Photoperiod and Temperature

Reliable methods have been developed for controlled spawning of captive southern flounder, Paralichthys lethostigma, broodstock during their natural winter (December–February) spawning season. From 1999 to 2004, we evaluated the effects of manipulation of photoperiod and temperature on both advance and delay spawning to produce viable embryos throughout the year. Wild‐caught adult broodstock were held in 4.8‐ to 7.0‐m³ controlled‐environment tanks at a sex ratio of approximately 12 females to 4 males. Broodstock were subjected to different artificial photothermal conditioning regimes: extended winter (EW), accelerated (A‐10‐, A‐6‐, A‐4.5‐, and A‐3.8‐mo regimes), and delayed (D‐16‐ and D‐14‐mo regimes), with gradual and abrupt transitions, respectively, from long to short daylengths. Under an EW cycle, fish were exposed to constant short daylengths (10 L: 14 D) after the winter solstice in January. Eighty‐seven natural spawnings from December to April produced 18.3 × 10⁶ eggs, with 20.9% hatching successfully (i.e., overall egg viability). Under an A‐10‐mo cycle, rate of decrease in daylength was accelerated after the summer solstice in July, to reach winter conditions in October. Seven induced spawning trials from October to November produced 897 × 10³ eggs, with 40.4% viability. Under an A‐6‐mo cycle, rate of change of photoperiod was accelerated after the winter solstice in January, to reach winter conditions in July. Three induced spawning trials in July produced 550 × 10³ eggs, with 14.7% viability. Under an A‐4.5‐mo cycle, broodstock exposed to EW from January through April were exposed to an accelerated cycle to reach winter conditions by October. Four induced spawning trials from September to November produced 729 × 10³ eggs, with 28.7% viability. Under an A‐3.8‐mo cycle, broodstock exposed to EW conditions from January through April were exposed to an accelerated cycle to reach winter conditions by September. Five induced spawning trials from September to November produced 510 × 10³ eggs, with 45.9% viability. Under a D‐16‐mo cycle, fish were exposed to a decelerated decline in photoperiod after the summer solstice in July, to reach winter conditions in May, when atretic females were observed. Under a D‐14‐mo cycle, fish were exposed to constant summer conditions from December through mid‐June and then to an abrupt decline in photoperiod to winter conditions in late June. Six induced spawning trials from September to November produced 763 × 10³ eggs, with 13.0% viability. Production of viable embryos was greatest during the extended winter because of abundant natural spawnings. While successful natural spawnings were rare during the fall or summer, viable embryos were produced through induced spawnings during all seasons of the year, with no significant (P > 0.05) differences in egg viability. Extended winter conditions prolonged spawning from 3 to 5 mo. Accelerated (3.8–10 mo) regimes were effective in producing viable embryos from summer through fall, but a minimum of 5 mo was required to complete gonadal recrudescence. While constant long daylengths after the summer solstice delayed gonadal recrudescence, with spawning obtained 2.5 mo after an abrupt reduction to short daylengths, a decelerated decline in photoperiod did not. Artificial control of daylength enabled precise control of gonadal recrudescence and year‐round spawning in southern flounder without adverse effects on the quality of eggs and larvae and will improve availability of seedstock for commercial aquaculturists.     

The Effects of Exogenous Bovine Growth Hormone and Placental Lactogen on Juvenile Striped Bass Morone saxatilis Feed and Growth Efficiency

Striped bass Morone saxatilis under normal pond-reared conditions usually requires 14–18 mo to grow out to market weight. This includes a winter of comparatively slower growth which could possibly be overcome through hormonally induced acceleration of growth. Thus, the objective of this experiment was to test the hypothesis that bovine growth hormone and bovine placental lactogen increase growth in striped bass in a dose dependent manner. A secondary objective was to determine the effect of these hormones on body composition. Variables tested were weight gain, length gain, condition factor, feed conversion, and body composition. Fish injected biweekly with 10 μg/g body weight, bovine placental lactogen ( P < 0.09) or bovine growth hormone ( P < 0.11) increased body weight. Fish injected with 1 or 10 μg/g body weight bovine placental lactogen ( P < 0.10) or bovine growth hormone ( P < 0.10) increased body length during the 12-wk study period. Proximate analysis indicated that bovine growth hormone increased protein content (10 μg/g; P < 0.10) and decreased fat content (1 and 10 μg/g; P < 0.10). No significant differences occurred in feed conversions. We conclude that bovine growth hormone and bovine placental lactogen are effective in increasing body growth in striped bass.     

Voluntary Spawning of Captive Nassau Groupers Epinephelus striatus in a Concrete Raceway

Nassau groupers Epinephelus striatus held in a 37-m³ concrete raceway were conditioned to spawn 3 mo later than in their home waters. After being held in the raceway for 15 mo, four female and two male groupers spawned voluntarily over a 4-d period in March 1994, producing 10.3 million eggs. By December 1994, two females had been removed. During March 1995, one of the remaining two females spawned on three consecutive days (60 cm TL, 1,172,000 eggs) and the other only on the third day (47 cm TL, 488,000 eggs). In April 1995, three females (including one held in isolation for 6 mo, then replaced 6 d before the first spawn) produced more than 9.8 million eggs in 4 d. The isolated female spawned 8 d after being placed in a cage in the raceway and 4 d after release in the raceway.
Individual females spawned as many as nine times a day for 1–4 d. Spawning occurred from 3.5 d before until 8.5 d after the full moon. A 30-d interval elapsed between March and April 1995 spawning periods. Fertilization was in the range 83–100% and hatching 90–100%. Spawns occurred in a temperature range of 23.1–27.9 C; however, based on spawning frequency and volume and on egg development, 24–27 C seems most suitable. These results and other evidence support the view that Nassau groupers can be conditioned to spawn any month of the year, mainly by manipulating temperature.     

Thermal habitat of striped bass (Morone saxatilis) in coastal waters of northern Massachusetts,USA, during summer

Striped bass, Morone saxatilis, were captured and released with temperature‐measuring data storage tags in Salem Sound, Massachusetts, to collect data on their thermal preferences in coastal and marine waters and to identify environmental factors that may influence temperatures experienced during their summer residence. Striped bass recaptured during summer of 2006 (21 of 151 releases) experienced a wide range of temperatures (6.5–28.0°C) while at‐large for 1–53 days. Overall mean temperature and standard deviation selected by striped bass recaptured in Salem Sound during the longest commonly‐shared duration of time (3–12 July) were 17.8 and 3.57°C, respectively. Comparison of temperature data between fish and 13 vertical arrays in Salem Sound revealed that striped bass experienced higher and more variable temperatures, and that daily changes in temperature actually experienced were unrelated to daily changes in surrounding ambient temperature. Regular cyclical changes in temperature of all striped bass and vertical arrays were identified as influences of the local tide, which contributed about a 2°C change in temperature, on average, over the complete cycle. Most striped bass appeared to limit their activities to depths shallower than the lower limit of the thermocline, above which temperatures generally exceed 9.0°C in Salem Sound. Therefore, it is likely that the vertical distribution of striped bass is restricted by the low temperatures below this depth. An implication of this finding is that the spatial distribution of striped bass may be defined coarsely by knowledge of the distribution of temperature in coastal areas.     

Multiple vitellogenins and product yolk proteins in striped bass,Morone saxatilis: molecular characterization and processing during oocyte growth and maturation

The multiple vitellogenin (Vtg) system of striped bass, a perciform species spawning nearly neutrally buoyant eggs in freshwater, was investigated. Vitellogenin cDNA cloning, Western blotting of yolk proteins (YPs) using Vtg and YP type-specific antisera, and tandem mass spectrometry (MS/MS) of the YPs revealed the complex mechanisms of yolk formation and maturation in this species. It was discovered that striped bass possesses a tripartite Vtg system (VtgAa, VtgAb, and VtgC) in which all three forms of Vtg make a substantial contribution to the yolk. The production of Vtg-derived YPs is generally similar to that described for other perciforms. However, novel amino-terminal labeling of oocyte YPs prior to MS/MS identified multiple alternative sites for cleavage of these proteins from their parent Vtg, revealing a YP mixture far more complex than reported previously. This approach also revealed that the major YP product of each form of striped bass Vtg, lipovitellin heavy chain (LvH), undergoes limited degradation to smaller polypeptides during oocyte maturation, unlike the case in marine fishes spawning buoyant eggs in which LvHAa undergoes extensive proteolysis to osmotically active free amino acids. These differences likely reflect the lesser need for hydration of pelagic eggs spawned in freshwater. The detailed characterization of Vtgs and their proteolytic fate(s) during oocyte growth and maturation establishes striped bass as a freshwater model for investigating teleost multiple Vtg systems.     

Mating and spawning of freshwater crayfish, Austropotamobius pallipes Lereboullet, under laboratory conditions

Abstract. The study includes mating and spawning data of freshwater crayfish, Austropotamobius pallipes Lereboullet, obtained in four consecutive years (1987–1990). A total number of 586 wild-caught female A. pallipes in the 21·65 mm to 45·60mm carapace length (CL) size were held under laboratory conditions at different dates in September–October. Initial densities at mating time were 21 and 24 crayfish/m² with a 1:2 male:female ratio. High percentages of mating were obtained (97·4–100%) except in 1989 (57·5%). In all years, most of the matings (90%) were concentrated in a period of 8–12 days with mean water temperatures between 12°C and 13·5°C. Spawning took place a few days after mating (minimum 2 days, maximum 14 days) at mean water temperatures between 8·2°C and 10·8°C. In the first 3 years, almost 100% of mated females spawned. However, in the fourth year (1990), when the mean size of crayfish was smaller, only 72·4% of mated females spawned. The mean number of pleopodal eggs was 64 (maximum 220, minimum 18). Egg diameter ranged between 2·30 and 3·25 mm (mean value 2·78 mm). Pleopodal egg number was positively correlated with carapace length ( r = 0·72).     

Purification,characterization and immunoassay of striped bass (Morone saxatilis) vitellogenin

The egg yolk precursor, vitellogenin (VTG), was purified from blood plasma of striped bass by chromatography on hydroxylapatite or DEAE-agarose. The fish were first implanted with estradiol-17β (E₂), which induced vitellogenesis. A rabbit antiserum (a-FSPP) raised against plasma from mature female striped bass, and then adsorbed with mature male plasma, was used to detect female-specific plasma protein (FSPP) in the chromatography fractions. Striped bass VTG (s-VTG) was collected from the peak fraction that was induced by E₂, reacted with a-FSPP, and contained all detectable phosphoprotein. It appeared as a single band (M_r ≂ 170,000) in SDS-PAGE or Western blots using a-FSPP, and as a pair of closely-spaced phospholipoprotein bands in native gradient-PAGE, suggesting that there is more than one circulating form of s-VTG. The relationship of s-VTG to the yolk proteins was verified using a-FSPP. The antiserum reacted with the main peak from gel filtration of saline ovary extracts, and it specifically immunostained the two main bands in Western blots of the extracts and the yolk granules of mature oocytes. The amino acid composition of s-VTG was similar to that of VTG from other fish and Xenopus. A radial immunodiffusion assay for s-VTG was developed using a-FSPP and purified s-VTG as standard. The s-VTG was not detected in blood plasma of males, immature females, or regressed adult females, but plasma s-VTG levels were highly correlated with plasma E₂ and testosterone levels, and oocyte growth, in maturing females. The results indicate that the maturational status of female striped bass can be identified by s-VTG immunoassay.     

Spatial and temporal patterns in the distribution and feeding habits of Morone saxatilis in marsh creeks of Delaware Bay, USA

Delaware River and Bay Morone saxatilis (Walbaum), striped bass, have recently undergone a dramatic recovery. Here, we examine spatio‐temporal patterns in the distribution and food habits of striped bass in marsh creeks in the estuary (salinity range 1–20 psu), 1996–2000. Sampling occurred monthly, April through November, with otter trawls (4.9 m, 6 mm mesh, n = 6760) and weirs (intertidal block nets, 6 mm mesh, n = 647) at eight sites. Young‐of‐the‐year (YOY) fish were generally more than 10 times more abundant at oligohaline sites, although they were abundant at mesohaline sites in 1996, the lowest salinity year. Small striped bass (<100 mm) in creeks relied on mysids and other crustaceans and became more piscivorous with size. Overall, they consumed 46% by weight fish, of which 52% were mummichog, Fundulus heteroclitus (L.), and 18% were YOY Atlantic croaker, Micropogonias undulatus (L.), prey types which are not typical in most food habits studies and are indicative of feeding in marsh creeks. These data suggest that young striped bass are an abundant component of Delaware Bay marsh creek fauna and may play an important role in trophic relays within this system.     

Hooking mortality of white crappie, Pomoxis annularis Rafinesque, and spotted bass, Micropterus punctulatus (Rafinesque), in Texas reservoirs

Abstract. This study was conducted to estimate spring hooking mortality of white crappie, Pomoxis annularis Rafinesque, in Buchanan Reservoir, Texas, USA and summer hooking mortality of spotted bass, Micropterus punctulatus (Rafinesque), in Eagle Mountain Reservoir, Texas, USA. Reservoir surface water temperatures averaged 19 and 31°C, during white crappie and spotted bass experiments, respectively. White crappie (mean total length (TL) 267mm, range TL 190–340mm, standard error (SE) TL 6mm) were caught with size 5 single hooks baited with golden shiner, Notemigonus crysoleucas (Mitchill), and spotted bass (mean TL 220mm, range TL 143–326mm, SE TL 7mm) were caught with artificial lures (spinners) fitted with size 4 or 5 treble hooks. Fish were held in cages for 72 h to observe delayed mortality. Four of 43 white crappie (9·3%, 95% one-tail, upper confidence limit (UCL) = 13·7%) died and four of 47 spotted bass (8·5%, UCL = 15·2%) died. One of the white crappie that died was a sublegal-length fish. The relevance of these findings to the management of white crappie and spotted bass sport fisheries is discussed. It is concluded that under any management strategy necessitating release of some portion of the catch of white crappie and spotted bass, high survival of that portion could be expected.     

Sperm Characteristics of Precocious 1-year-old Male Striped Bass Morone saxatilis

Abstract.— Captive-reared, 10-mo-old, male striped bass Morone saxatilis were sampled monthly for testicular development between February and June 1994. One of the five males sampled in February showed precocious testicular development and had a gonado-somatic index (GSI) of 1.26%. while the other four fish had immature testes with a mean GSI ± s^x, of 0.17 ± 0.03%. Spermiating individuals were present from April to June. In April the average body weight (BW) of spermiating males was 65 ± 4 g and their GSI reached a mean value of 4.75 ± 0.52%. In June, milt collected from ten precocious males contained motile spermatozoa with a mean of 31 ± 7% of the sperm showing forward movement. Mean milt volume and sperm concentration were 1.67 ± 0.41 mL/kg BW and 92.3 ± 1.8 ± 10⁹ spermatozoa/mL. respectively. These data show that male striped bass reared in captivity can reach sexual maturity during their first year. This is one year earlier than previously reported for striped bass in mid-Atlantic regions.     

GnRHa‐induced Multiple Spawns and Volition Spawning of Captive Spotted Rose Snapper,Lutjanus guttatus,at Mazatlan,Mexico

Sexual maturation and induced spawning treatments were carried out with captive spotted rose snapper, Lutjanus guttatus. A total of 3013 × 10⁶ eggs (64.7% were floating) were produced from eight treated females in 42 spawns induced with GnRHa implants during the course of the present study. GnRHa ethylene‐vinyl acetate copolymer effective doses were 204 ± 11 µg/kg in June 2005, and 224 ± 13 µg/kg in July 2005. General fertilization was 50.9 ± 34.5% and 12–14 h after spawning, viability of floating eggs was 90.4 ± 12.4%. Mean incubation period at 29–31 C was 18–20 h, and mean hatching was 94.4 ± 8.2% (73–100%). Newly hatched larvae were 2.18 ± 0.15 mm in total length (TL). One month after the last hormone experiment, previously GnRHa‐treated and untreated fish began spawning voluntarily. Hormone‐treated breeders had higher fecundity than untreated fish, producing 72.5 million eggs versus 13.9 million eggs for the untreated fish, over the following 11 mo. Combined data of volitional spawning for total egg fertilization, viability, hatching, and larval TL were 77.7 ± 1.8%, 90.3 ± 1.3%, 87.9 ± 2%, and 2.50 ± 0.12 mm, respectively. These results can ensure the sustainability of a commercial hatchery.     

Oocyte Growth in the Striped Mullet Mugil cephalus L. Maturing at Different Salinities

Profiles of oocyte growth were obtained from female striped mullet Mugil cephalus L. held in salinities ranging from fresh water to seawater during two consecutive spawning seasons (1988–1990) in Hawaii. Females underwent vitellogenesis at all salinities (i.e., 32–35, 13–20, and 0%‰) tested. Females maturing in fresh water exhibited a slower rate of oocyte growth, and a significantly lower number completed vitellogenesis. All females were induced to spawn in full seawater. The number of fertilized eggs per spawning was highest from females maturing in brackish water. More females were able to be induced to spawn twice in brackish water during the 1989–1990 season than in fresh or seawater. The results from the current investigation suggest that salinities ranging from 13–35 ppt are adequate for ovarian maturation in captive striped mullet females.