Post-spawning Season Research Articles

Reproductive biology of the dusky grouper Epinephelus marginatus (Lowe, 1834)

Investigations were carried out about the reproductive biology of the dusky grouper, Epinephelus marginatus (Lowe, 1834) a serranid protogynous hermaphrodite fish inhabitant of rocky bottoms from shallow waters up to 200 m depth. Samples were caught in the islands that form Arvoredo Biological Marine Reserve (SC - Brazil) and the coastal islands near Florianópolis region from March 1998 to May 2000. Data from samples of juvenile groupers on intertidal pools were used to link their occurrence in the pools to the post-spawning season. To describe the histological changes on gonads along the reproductive cycle and to establish maturation scales, 109 groupers were histologically tested for sex determination. First maturation size was determined for females (L50=470 mm; r²=0.99). The results of calculated gonadosomatic (GSI) and hepatosomatic (HSI) indexes, showed that maturation occurred along the spring months and the spawning activity during the summer with a peak in December. Liver recovery (HSI elevation) was evident in the autumn, was the post spawning season. The relationship between length and weight was W = 9 · 10-6 · TL3.1149 (r²=0.998; n=246).

The effects of exogenous androgens on ovarian development and sex change in female orange-spotted protogynous grouper, Epinephelus coioides

The efficacy of various doses of an androgen mixture, containing testosterone (T), 17α-methyltestosterone (MT), and testosterone propionate (TP) in equal ratios, for induction of sex change in protogynous orange-spotted grouper, Epinephelus coioides, was examined. The androgen mixture, with doses from 1 to 20,000 μg/kg BW, was implanted into each fish (body weight 1.7 kg) in July (post-spawning season), and gonadal stage and plasma T were monitored at various time intervals for a period of 90 days. Gonadosomatic (GSI) and hepatosomatic indices (HSI), gonadal histology, sex steroids (T, 11-ketotestosterone=11-KT, and estradiol=E2) in plasma were determined after 90 days of implantation. The implanted T was released to plasma for 60 days. All androgen mixtures at doses higher than 1000 μg/kg BW were capable of inducing a sex transition and completion of spermatogenesis up to the functional male phase. Low doses of androgens induced ovarian development and higher GSI and HSI indices than in the control and other groups. Significantly higher plasma T levels were found in the developing and spermiating males as compared to the females and intersex-transitional fish. No significantly difference of plasma levels of E2 and 11-KT was found in the control and all the androgen-treated groups (during the nonreproductive season). Therefore, it is concluded that the stimulation of sex change or ovarian development is dependent on the dose and time course of implanted androgens. Plasma T levels were correlated with the development of controlled male phase in protogynous grouper, E. coioides.

Comparison of Total Mortality of White Grunt from the Headboat Fishery on the Gulf Coast of Florida during Spawning and Postspawning Seasons

White grunts Haemulon plumieri were sampled from catches of the headboat fishery operating on the Gulf Coast of Florida to determine sex-specific total mortality by using catch curve analyses. Sampling was conducted during the peak of the spawning season (April–June) and in a postspawning season (July–October). In total, 1,051 white grunts were sampled in the spawning season, and 1,141 were sampled in the postspawning season. Recruitment to the fishery occurred at age 2, and the majority of males and females landed in the fishery during both the spawning and postspawning seasons were ages 2–4. The maximum age of females sampled was 18 years; for males, the maximum was 15 years. Instantaneous total mortality (Z) estimates from the catch curves did not differ significantly between spawning females, spawning males, postspawning females, and postspawning males; the pooled Z was estimated to be 0.357 (95% confidence interval, 0.284–0.430). Total annual mortality (A) was therefore estimated to be 30% (95% confidence interval, 25–35%). Total annual mortality estimates based on Robson–Chapman survival estimates were similar for females (28% and 30% for spawning and postspawning females, respectively) but were slightly greater for males (37% and 38%, respectively).

Seasonal variation of plasmatic and hepatic vitellogenin and EROD activity in carp, Cyprinus carpio, in relation to sewage treatment plants

Concern about the health of aquatic fauna living in waters containing biologically active levels of estrogenic compounds is particularly focused on the effects on their reproductive success. To that end, carp, Cyprinus carpio, a feral fish living in warm waters of Southern Europe (NE Spain), were selected for signs of estrogenicity. The study area covered two tributaries (the Anoia and the Cardener) of the Llobregat River both known to be polluted by estrogenic compounds. The estrogenicity in the carp was measured as vitellogenin (VTG) presence in males and alterations in VTG levels in females, over a 6-month period, embracing both the pre- and post-spawning seasons. VTG content was measured in both the plasma and liver, the latter being the organ that synthesizes it. Also, hepatic 7-ethoxyresorufin O-deethylase (EROD) activity was recorded, as interactions of xenoestrogens and oestradiol have been reported to affect this enzymatic activity. The estrogenicity of these rivers was more evident in the Anoia at the location downstream from the sewage treatment plant (STP), by elevated levels of VTG in males and by the presence of some intersex individuals. In the Cardener, no intersex fish were found and male plasmatic VTG was not so highly elevated. However presence of hepatic VTG, in up to 54% of the male fish analyzed, proved exposure to xenoestrogens. In females, VTG fluctuated according to the biological cycle with a plasmatic peak in May and an earlier maximal in the liver. However, this pattern was altered in the locations with higher xenoestrogens presence. EROD activity showed differences between sexes, with higher activity in males than females, as well as site-related differences (up to one order of magnitude) in the same river. These differences were even greater than those detected between rivers. A seasonal trend was also seen in EROD activity with higher induction towards the summer in both males and females.

Oocyte development in summer flounder: seasonal changes and steroid correlates

Seven ovarian stages are described in summer flounder Paralichthys dentatus. In the prespawning season plasma oestradiol levels increased in maturing fish with lipidogenic oocytes and gonadosomatic index increased in fish undergoing vitellogenesis. Atretic oocytes present in the postspawning season indicated which individuals may have spawned. The pattern of oocyte development is similar to that of other flatfishes and some teleosts. The summer flounder was unusual in having a long lipid uptake phase (oocyte diameter up to 301 μm) prior to any indication of vitellogenin (yolk protein) uptake. This information will be useful in the construction of an updated maturity schedule for the wild population.

Precocious ovarian recrudescence and induced off-season spawning of Heteropneustes fossilis by D-Lys6 salmon gonadotropin releasing hormone analog (sGnRH-A)

The feasibility of photothermal treatment and use of salmon gonadotropin releasing hormone analogue (sGnRH-A) for induced spawning of Heteropneustes fossilis outside the spawning season was investigated. Fish were maintained at 30° C and 14 h light (L)/10 h dark (D) for 60 days between the post-spawning season and preparatory season. Fish attained gonadal maturity 4 months earlier compared to the natural spawning season. Mature fish were induced to spawn by D-Lys6 sGnRH-A at a dose of 25 μg kg−1 body weight. The eggs obtained were fertilizable. Injection of D-Lys6 sGnRH-A at different time points during the photodiurnal cycle did not influence the latency period and spawning of H. fossilis.

Settlement and post-larvae behaviour of Mytitus galtoprovincialis: field and laboratory experiments

Field sampling carried out in the Ria de Vigo (NW Spain) from 1991 to 1993 showed that Mytilus gallopro\rincJa!Js settle dtreclly from the plankton onto substrates exposed to various environmental conditions: exposed rocky shore; protected rocky shore; exposed, raft mussel-culture area; and protected. raft mussel-culture area. For direct settlement, competent larvae may use a wide variety of substrates: filamentous nylon ropes; the byssus and intricately arranged material m the boLtom of mussel beds; filamentous, thallus and membranous algae; and rugostties on adult mussel shells. The peak of settlement occurred from spring to early autumn and differences in the settlement abundance among localities were influenced by currents. After this peak, the settlement of larger post-larvae continued, associated with the increase in storms during autumn that detach them from their original substrates. This dispersion phase allows for the possibility of colonising, or recmiting on other areas. even during the post-spawning season when the presence of small post-larvae is at its minimum. Laboratory experiments carried out with post-larval stages from 0.250 to 2.000 mm showed that under static water conditions they crawl and form clumps, but do not search for a specific substrate. If they are not disturbed, they may remain in their original place or settlement. Conversely, under moving water conditions they attach to a wide variety of substrates. particularly to byssal filaments and thalli of red algae Ceramium rubrum. The contact and attachment to substrates is carried out with a long mucous thread that also aids in forming dumps. The use of this mucus to settle results in a 'preference' for natural lilamentous substrates but also in setUement on rugous hard surfaces. An alternative hypothesis to the primary and secondary settlement pattern previously described in the literature for Myt1lus edulis is suggested.

Absence of 1-Methyladenine Production in Follicle Cells Obtained from Starfish Ovaries in the Post-Spawning Season: (starfish follicle celis/1-MeAde/GSS/cAMP/post-spawning season).

Follicle cells from the ovaries of starfish Asterina pectinifera collected in the breeding season and then kept in an aquarium for three months did not produce 1-methyladenine (1-MeAde) in response to genad-stimulating substance (GSS). The cyclic AMP content of follicle cells of the ovaries was much lower in the post-spawning season than in the spawning season. In the post-spawning season, the cyclic AMP level was increased slightly by GSS, but nor insufficiently for production of 1-MeAde. Addition of 3-isobutyl-1-methylxanthine, a potent phosphodiesterase inhibitor, stimulated the productions of GSS-induced 1-MeAde and cyclic AMP. Adenylate cyclase in membrane preparations of follicle cells from ovaries in the post-spawning season was stimulated by nonhydrolyzable GTP analogs and forskolin. An experiment on ADP-ribosylation with [α-32 P]NAD in the presence of cholera toxin and pertussis toxin showed the presence of two types (stimulatory and inhibitory) of guanine nucleotide-binding regulatory proteins (G-proteins). However, GSS has no effect on the adenylate cyclase activity regardless of the presence of GTP. These findings suggest that GSS does not bind to its receptor in follicle cells of the overy in the post-spawning season, although these cells possess G-proteins and adenylate cyclase. Thus the absence of 1-MeAde production by follicle cells obained from ovaries in the post-spawning season appears to be due to lack of receptor protein for GSS.

Changes in hypothalamic monoamine oxidase activity in relation to 17β-estradiol and clomiphene citrate treatments in the teleost Channa punctatus during three seasons

Hypothalamic monoamine oxidase (MAO) activity displayed biphasic responses to administration of estradiol-17β (E 2) depending on season. Lower doses of 0.05 and 0.10 μg/g BW of E 2 had enhanced enzyme activity and higher doses (0.5 and 1.0 μg/g BW) depressed it significantly in preparatory season. In prespawning phase, the lowest dose of 0.05 μg/g BW of E 2 was stimulatory and the higher doses were inhibitory to MAO activity. In postspawning season, lower doses (0.05 and 0.10 μg/g BW) of E 2 failed to elicit any significant change in enzyme activity whereas the higher doses (0.5 and 1.0 μg/g BW) elevated it significantly. Administration of clomid (5, 10, and 20 μg/g BW) inhibited MAO activity in a dose-dependent manner during all the three seasons. The results show that E 2 may participate in feedback control of gonadotropin secretion by modifying monoaminergic activity at the level of oxidative deamination by MAO.

Seasonal effects of administration of melatonin and 5‐methoxytryptophol on ovarian activity in the catfish Heteropneustes fossilis (Bloch)

In Heteropneustes fossilis, effects of intraperitoneal administration (25 micrograms/fish, alternate days for a month 1 hr before the onset of dark phase) of melatonin (MEL) and 5-methoxytryptophol (5-MTL) on ovarian activity were investigated during different seasons of the annual reproductive cycle under natural photothermal conditions. The gonadosomatic index (GSI) had decreased significantly by MEL during preparatory and prespawning seasons, and by 5-MTL in all but the spawning season. Both MEL and 5-MTL administrations arrested vitellogenesis during the gonadal recrudescence phase. As a result, stage I previtellogenic oocytes showed a significant increase in the MEL group in the preparatory and prespawning seasons, and in the 5-MTL group only in the prespawning season. Almost the same trend was noticed in the percentage distribution of stage 2 and 3 oocytes. The percentage distribution of stage 4 postvitellogenic oocytes decreased significantly during the preparatory and prespawning seasons, but not in the spawning season. The indole treatment resulted in a highly significant increase in the percentage distribution of atretic oocytes during prespawning, spawning, and post-spawning phases. Total protein content of the ovary was significantly lower in all seasons after MEL treatment, and only in the preparatory and prespawning seasons following 5-MTL treatment. The ovarian glycogen level was significantly lower in the preparatory and prespawning seasons (MEL group), and in the 5-MTL group only in the prespawning phase. Ascorbic acid level was inhibited by the indole treatment in all seasons except in the 5-MTL group during the post-spawning season. The results show that both MEL and 5-MTL are effective in inhibiting ovarian vitellogenesis and inducing atresia in the catfish.

Effects of temperatures during winter on gonadal recrudescence in spring in the rose bitterling Rhodeus ocellatus ocellatus.

The rose bitterling Rhodeus ocellatus ocellatus, Cyprinidae, a spring and summer breeder, were captured in out of the breeding season (early November). They were divided into three temperature groups (5, 10, and 15°C), and reared under a short photoperiod (1OL-14D) for 60 days. Then each group was divided into two photoperiod groups; a long (14L-10D) and the short (continued) photo-period group, and all the groups were kept at 15°C for another 37 days. In females gonadal re-crudescence did not occur in any temperature group during first 60 days. However at the end of the experiment (late February), gonadosomatic indices (GSIs) of ovaries had significantly increased in all the long photoperiod groups. On the other hand, only the females pre-treated by warmer temperatures (10 and 15°C) for 60 days showed some gonadal recrudescence under the short photo-period. Male bitterling represented almost the same pattern of the change of GSIs during the experiment, but some individuals had attained the spermiogenesis in all the groups at the end of the experiment. These results indicate that in the post spawning season, the photoperiodism in-volved in maturation of the rose bitterling declines under natural temperatures of late autumn (10-15°C). Low temperatures of winter do not seem to be essential for the gonadal maturation in spring during the annual reproductive cycles of this species.

Changes in hypothalamic catecholamine levels in relation to season, ovariectomy, and 17β-estradiol replacement in the catfish, Clarias batrachus (L.)

In female Clarias batrachus, hypothalamic levels of noradrenaline (NA) and dopamine (DA) exhibited seasonal changes during different phases of the annual reproductive cycle. The NA level was high during gonadal recrudescence (prespawning and spawning phases) and low during gonadal quiescence (postspawning and resting phases). A reverse trend was noticed in the DA level. After 3 weeks of ovariectomy (Ovx), the catecholamine (CA) levels were elevated significantly in the preparatory, prespawning, and spawning phases and were unaltered in the postspawning season. Administration of 17β-estradiol (E 2, 1.0 μg/g BW) to 3-week Ovx fish resulted in both seasonal and differential effects on the CA levels. The NA level was significantly elevated in the preparatory phase, decreased in the prespawning and spawning phases, and remained unaltered in the postspawning season. The DA level was restored by the steroid treatment in the preparatory phase, but registered a significant elevation in the prespawning and spawning phases. In the prespawning phase, Ovx induced a significant elevation of the hypothalamic NA level after 2, 3, and 4 weeks, but was significantly low after 5 weeks. The DA level registered a significant increase after 2, 3, and 5 weeks of Ovx. Administration of E 2 to 3-week Ovx fish elicited dose-dependent responses on CA levels. The administration of a low dose of E 2 (0.05 μg) caused a significant elevation of the NA level, while the 0.1 μg dose did not alter the amine level in comparison to that of the Ovx vehicle group. The higher doses (0.5 and 1.0 μg) of E 2, however, decreased the NA level significantly below that of the sham vehicle and Ovx vehicle groups. The DA level was unchanged in the 0.05-μg group and registered a significant increase at 0.1, 0.5, and 1.0 μg/g doses of E 2. The results suggest that changes in the circulating level of E 2 may influence hypothalamic CA which, in turn, may modulate the secretion of gonadotropin from the pituitary.

Differential effects of photoperiod and temperature on hypothalamic monoaminergic activity in the teleost Channa punctatus (Bloch)

In Channa punctatus maintained under ambient photothermal conditions (10.5L:13.5D; 13 ± 2°C) in the postspawning season, hypothalamic dopamine (DA) and norepinephrine (NE) content varied diurnally, but serotonin (5-HT) and monoamine oxidase (MAO) did not. Exposure of the fish to high temperature (25 ± 2°C), with or without altering the photopheriod, increased the NE and DA content, and NE turnover but decreased DA turnover. Increasing the photoperiod (16L:8D) alone had no significant effect on catecholaminergic (CA) content or activity. When the fish were exposed to long photoperiod, with or without altering the temperature, a day-night variation in 5-HT content and activity was induced in the postspawning season. An increase in temperature alone had no significant effect on 5-HT content or activity. Hypothalamic MAO activity was elevated in fish exposed to high temperature alone, or in combination with long photoperiod, but was not affected significantly by long photoperiod treatment. These results indicate that CA activity is influenced largely by ambient high temperature, whereas serotonergic activity is controlled primarily by photoperiod, with high temperature having an additive effect. MAO activity seems to be influenced by both temperature and photoperiod in this species.

Effects of Season, Pinealectomy, and Blinding, Alone and in Combination, on Hypothalamic Monoaminergic Activity in the Teleost Channa punctatus (Bloch)

In Channa punctatus, day-night variations in hypothalamic 5-HT (serotonin) and monoamine oxidase (MAO) activity were noticed in preparatory but not other phases (prespawning and postspawning) of the annual reproductive cycle. Hypothalamic MAO, 5-HT, and norepinephrine (NE) activity was found to be high in the prespawning phase and low in the postspawning phase. Dopamine (DA) activity, on the other hand, was high in the postspawning season and low in the prespawning phase. Pinealectomy caused season-dependent effects on hypothalamic monoaminergic activity, with a significant increase in serotonergic activity and a significant reduction in MAO activity at midscotophase during the preparatory phase (March) but not in the prespawning (May-June) or postspawning (September) phases. Hypothalamic catecholaminergic (CA) activity was not influenced by pinealectomy during any of the seasons. To determine whether or not the photoperiodic influences on daily variations of 5-HT and MAO in the preparatory phase are mediated via pineal and/or lateral eyes, fish were pinealectomized and/or blinded in January, when there is no rhythm, and sacrificed in February, when a day-night variation normally sets in. The day-night difference in 5-HT content and activity and MAO activity was not abolished by pinealectomy or blinding alone; but the combination (pinealectomy + blinding) obliterated the daily variation only in 5-HT content and in MAO activity. However, pinealectomy and blinding, alone or in combination, caused a significant elevation of 5-HT activity (not its level) and a significant decrease in MAO activity at midscotophase, with the combination having an additive effect. Hypothalamic CA content or activity was not affected by these regimes. The results show that photoperiodic influence on the daily pattern of 5-HT and MAO activity is mediated through and by the interaction of the pineal and lateral eyes.

Annual reproductive cycle of the topmouth gudgeon Pseudorasbora parva in the Tama River.

Adult topmouth gudgeon Pseudorasbora parva (Cyprinid) were collected monthly for a year in the midstream of the Tama River, Tokyo. Gonadosomatic indices (GSI) and gonadal histology were used as criteria of gonadal maturation. During March and April male and female GSIs in-creased rapidly with the accumulation of yolk globules and active spermatogenesis, respectively. GSIs stayed high during April, May, and June, but decreased drastically in July showing the end of their spawning season. In the post spawning season (August) the ovaries and the testes were filled with yolkless oocytes and proliferating spermatogonia, respectively. During autumn and winter a gradual gonadal recrudescence which was represented by the accumulation of yolk vesicles or meiosis of spermatocytes occurred. These results indicate that the spawning season of P. parva extends from the end of March to the end of June in this sampling area. A possible environ-mental control on the annual reproductive cycles of this species was discussed.

Radiomanganese distribution to female and male of Haliotis discus at the post-spawning stage.

Immediately after spawning had occurred in the eazly stage of exposure experiment, the female individuals exposed to 54Mn concentrated more actively the nuclide than the males, and retained it in whole bodies at 1.70 times higher compared to the males in 100%-SW. Moreover, the biological half-life estimated from the excretion formula was 1.58 times longer in the females than in the males, i.e.54Mn in the females was eliminated more gradually than that in the males. These results differed clearly from those obtained on H. discus at the pre-spawning stage and furthermore, from stable-Mn distribution observed in females and males of Mytilus edulis at the post-spawning season presented previously elsewhere. 54Mn distributed to various soft tissues in the females were apparently higher than those in the males at the end of the exposure in 100%-SW. The concentration factor for ovary of specimens in 100%-SW raised up to 990 at the end of the exposure, while that of sperrnary was only 146. The difference between that for thc ovary and the spermary was of the highest value among tissues, and consequently a skmilar correlationship existed in absolute arnounts and concentrations. The distribution of 54Mn to ovary exhibited skmilar trend at the pre- and the post-spawning stages, but its degree differed from each other and was enhanced in concentration at the latter stage. The nuclide uptake, retention and excretion by the females were inhibited under depressed spccific gravity condition, whereas the males were not affected at all.

Condition factor ofAmblypharyngodon chakaiensis Babu and Nair in the Chakai boat channel (Trivandrum-Kerala-India)

Condition factor (K) and relative condition factor (K n ) ofAmblypharyngodon chakaiensis Babu and Nair males and females respectively have been studied in relation to the various months of the year and length groups. No significant correlation exists between the proportion of the males in the population and value of condition factor (K). On the basis ofK andK n and the various length groups in respect of males and females are arranged into three classes and their incidence in the pre-spawning, spawning and post-spawning seasons were represented. In femalesK n showed significant positive correlation with gonadosomatic index. The size at first maturity observed by direct observation of the gonads in females and males agrees with the inflexions on the curve depictingK andK n with respect to length groups. The influence of feeding intensity onK does not seem to be quite apparent inA. chakaiensis. The steady fall inK in the males seems to be related to the decrease in the percentage occurrence of males of these length group in the sample.

Estradiol-17β effects on lipid and carbohydrate metabolism and on the induction of a yolk precursor in goldfish, [formula omitted][formula omitted

The effects of estradiol-17β treatment on plasma lipid levels, liver lipid and glycogen reserves were examined during different phases of the reproductive cycle in goldfish, Carassius auratus . Estrogen therapy resulted in increased plasma and hepatic lipid levels except during the spawning season. Hepatic glycogen deposits were depleted by estradiol injections during all seasons. Treatment of fish with the estrogen antagonist, CI-628, during the spawning season caused a reduction in plasma and liver lipid levels. Electrophoretic studies conducted during the post-spawning season showed that estrogen induces the appearance of a specific lipoprotein, probably a yolk precursor, in the serum and liver of goldfish.

EFFECTS OF PHOTOPERIOD AND TEMPERATURE ON GONADAL ACTIVITY IN THE CYPRINID TELEOST, NOTEMIGONUS CRYSOLEUCAS

1. The effects of various photoperiod-temperature regimes on gonadal activity in the cyprinid teleost, Notemigonus crysoleucas, were examined during several different phases of the annual reproductive cycle.2. Regardless of the time of year when the experiment is initiated a long photoperiod-warm temperature regime stimulates gonadal development to the prespawning condition or induces spawning. Neither a warm temperature alone nor a long photoperiod alone will stimulate final gonadal maturation.3. Notemigonus is not refractory to long photoperiod-warm temperature gonadal activation during the postspawning season.4. Short photoperiods in combination with warm temperatures cause gonadal regression in this species. A low temperature-short photoperiod regime does not induce gonadal involution.5. Spermatocyte formation and proliferation as well as the early phases of vitellogenesis occur independently of environmental factors. Final gonadal maturation and the rate of gametogenesis, however, depend on specifi...

Independency of the adrenocortical cell from hypophyseal control as elucidated in hypophysectomized bullfrogs.

This paper deals with the morphological evidence of the independency of the adrenocortical cells in bullfrogs from pituitary control. Male adult bullfrogs (Rana catesbeiana) were hypophysectomized during the hibernation period. Six days after hypophysectomy atrophy of cortical cells was indistinct: the spherical summer cells of Stilling containing lots of acidophilic granules increased in number, in particular remarkably so in the deeper areas of the gland, and the polygonal possible “intermediate cells” between the summer and the lipid cell multiply simultaneously. Nine days after the removal, lipid cells were not yet profoundly degenerated, but the heavily vacuolated lipid cells were more frequently found. On the contrary, summer cells decreased in number and lost their acidophilic granules. Irrespective of hypophysectomy, mitotic cells were often detected in the immature lipid cells. When bullfrogs were hypophysectomized during the breeding period and post-spawning season, the lipid and acidophilic summer cells underwent no affections 10 days after the operation. Thus, the intrinsic seasonal variation during the breeding period and post-spawning period was not modified by hypophysectomy. The neoformation of lipid cells following hypophysectomy during the hibernation period suggested that the adrenocortical cells in bullfrogs might be less controlled by the hypophysis.