No abstract

Puberty is the period during which full sexual development occurs and the capacity to reproduce is acquired. Despite its importance, our understanding of the endocrine regulation of puberty in lower vertebrates is still limited. The objective of the present study was to describe the changes in gonadal development and plasma steroid levels in a relatively late maturing species, the striped bass, during the first four years of life. In about 65% of the females, puberty was initiated during the third year. Although gonadosomatic index (GSI) and oocyte diameter increased during this year, this first cycle was characterized by a heterogeneous population of developing oocytes, a relatively low mean maximum oocyte diameter, and an absence of yolk granules in the oocytes. Plasma 17β‐estradiol (E2) levels were low in all three‐year‐old fish, suggesting that an insufficient stimulation of vitellogenin production by E2 may underlie the lack of vitellogenin incorporation into developing oocytes. All monitored parameters increased during the fourth year, but were still below the values attained by older females. In about 60% of the males, puberty was initiated during the first year and all males were mature by the third year. During the first two years, several immature males initiated spermatogenesis without reaching full maturity. In mature males, mean GSI, plasma testosterone, and 11‐ketotestosterone levels increased simultaneously, reaching higher values each subsequent year. Our results indicate that, similar to the situation in mammals, more than one reproductive cycle is required in striped bass before complete adulthood is reached. J. Exp. Zool. 286:49–63, 2000. © 2000 Wiley‐Liss, Inc.

In most vertebrates, the development of a mature gonadotropin-releasing hormone (GnRH) secretory system is pivotal for the onset of puberty. The role of the three native GnRH forms, seabream (sb) GnRH, chicken (c) GnRH-II and salmon GnRH, in striped bass puberty remains elusive. This study examined the changes in pituitary GnRH levels throughout juvenile and pubertal development, a period encompassing 3 to 4 years. The levels of the two most abundant forms in the pituitary, sbGnRH and cGnRH-II (10:1), increased during the Fall and peaked prior to (cGnRH-II) or during (sbGnRH) the natural breeding season in March to May. In most cases, sbGnRH and cGnRH-II levels of maturing fish correlated to changes in oocyte diameter, gonadosomatic index and LH pituitary content. Interestingly, pituitaries of immature and maturing 2-and 3-year-old males and females contained similar amounts of all three GnRH forms. Additionally, pituitary sbGnRH and cGnRH-II levels in juvenile fish were relatively high and GnRH profiles showed a clear seasonality, similar to those of older, mature fish. These findings suggest a role for both sbGnRH and cGnRH-II in the regulation of gonadal development and indicate that, unlike some mammalian species, the timing of puberty in striped bass is not limited by a low activity of the GnRH system.

No abstract

The description of the heterotrophic dinoflagellate Pfiesteria piscicida as the causative agent of fish lesions and deaths along the mid-Atlantic estuaries has revealed the need for bioassays to assess its potential toxigenicity. We designed a bioassay in which fish are exposed to clonal dinoflagellate strains or environmental consortia (e.g. environmental water or sediment samples) in 750-mL culture flasks, and examined the relationships among dinoflagellate proliferation profiles, the presence of P. piscicida and fish deaths. Assay development and characterization were accomplished with dinoflagellate clonal cultures (P. piscicida, Karlodinium micrum, Prorocentrum minimum, CCMP1828, CCMP1829, and CCMP1834) co-incubated with sets of two young adult sheepshead minnows (Cyprinodon variegatus). Variables characterized included water quality (pH, dissolved oxygen, ammonia, nitrate and nitrite concentrations), the effect of the presence of fish on the proliferation and compositions of protist (dinoflagellate, protozoa, diatom) and bacterial populations, and time of fish death. The presence of fish in experimental flasks induced proliferation of P. piscicida and Cryptoperidiniopsis sp. (but not K. micrum or P. minimum) with populations rising between days 6 and 10, and declining 4 to 5 days later. Some fish deaths occurred when or soon after P. piscicida cell numbers were maximal. We conclude that this assay enables the assessment of acute effects of ichthyocidal dinoflagellates on fish during the first 10 days (Stage A) of the experimental course. Fish deaths during the subsequent 10 to 20 days (Stage B) may be attributed to the proliferation of ichthyocidal dinoflagellates, pathogenic bacteria and/or deteriorating water quality, whereas those beyond a period of approximately three weeks (Stage C) can be most certainly attributed to deteriorated water quality. Application of the flask assay to environmental samples [n=53] yielded fish deaths in all three stages: A, 78%; B, 11%, and C, 2%, with fish still living in 9% of the sample waters tested at the conclusion of the experiment beyond three weeks. The majority of samples that resulted in fish death in stage A tested positive for P. piscicida by PCR. If implemented with cautious interpretation, this assay should prove useful in monitoring blooms for the presence of P. piscicida and other dinoflagellate species potentially harmful to fish.