Serge I. Doroshov

Observations on the reproductive cycle of cultured white sturgeon, Acipenser transmontanus

Males and females of cultured white sturgeon, Acipenser transmontanus, mature at an average age of 4 and 8 years, respectively. However, the onset of ovarian vitellogenesis and puberty are highly asynchronous in the female stock. Gonadal cycles are annual in males and biennial in females, and gametogenesis is influenced by season. Neuroendocrine regulation of reproduction appears to involve a dual gonadotropin system controlling gonadal development and spawning. Labile puberty and sex-specific duration of the gonadal cycle are distinct characteristics of cultured and wild sturgeon. Photoperiod and temperature play a significant role in environmental regulation of the reproductive cycle, but further studies are necessary to elucidate the roles of endogenousand environmental factors in sturgeon reproduction which is critically important for both aquaculture and conservationof endangered wildstocks.

Observations on the reproductive cycle of cultures white sturgeon, Acipenser transmontanus

Males and females of cultured white sturgeon, Acipenser transmontanus, mature at an average age of 4 and 8 years, respectively. However, the onset of ovarian vitellogenesis and puberty are highly asynchronous in the female stock. Gonadal cycles are annual in males and biennial in females, and gametogenesis is influenced by season. Neuroendocrine regulation of reproduction appears to involve a dual gonadotropin system controlling gonadal development and spawning. Labile puberty and sex-specific duration of the gonadal cycle are distinct characteristics of cultured and wild sturgeon. Photoperiod and temperature play a significant role in environmental regulation of the reproductive cycle, but further studies are necessary to elucidate the roles of endogenous and environmental factors in sturgeon reproduction which is critically important for both aquaculture and conservation of endangered wild stocks.

Reproductive conditions of the Atlantic sturgeon (Acipenser oxyrinchus) in the Hudson River

Ninety-four prespawning adult Atlantic sturgeon (Acipenser oxyrinchus) were sampled in the Hudson River for age, sex, body size, gonad weight, fecundity, mature oocyte size, and plasma concentrations of gonadotropins, sex steroids, and vitellogenin during the spring spawning migrations in 1992 and 1993. In males, the age and total length ranged from 12 yr to 19 yr and from 133 cm to 204 cm and in females from 14 yr to 36 yr and from 197 cm to 254 cm. The majority of males were 13–16 yr old, and females were 16–20 yr old. Some females had residual atretic ovarian bodies, presumably remaining from a previous spawning and indicating iteroparity. Pre-ovulatory condition was recognized by migration of the germinal vesicle or by germinal vesicle breakdown and by significantly elevated plasma gonadotropins, progesterone, and vitellogenin. All pre-ovulatory females were captured upriver from Hudson River kilometer 136. Individual fecundity ranged from 0.4 million to 2.0 million eggs and oocyte diameter from 2.4 mm to 2.9 mm, and both characters exhibited a significant (p<0.05) positive relationship with female body size. Iteroparous females, tentatively identified by the presence of atretic bodies remaining in the ovary from a previous spawning, had significantly (p<0.05) higher fecundity and produced larger eggs, compared with females spawning presumably for the first time.

Enhanced survival in striped bass fingerlings after maternal triiodothyronine treatment.

Elevation of the triiodothyronine (T3) content of striped bass (Morone saxatilis) eggs by maternal T3 injection confirms the uptake of T3 by oocytes. The resulting offspring were influenced favorably by the T3, as seen in quantitative indices of development. As reported previously, larvae from T3-supplemented eggs raised under laboratory conditions exhibited increased body area, length, dry weight, and rates of swimbladder inflation and survival, compared to controls. Also, the T3 content of unfertilized oocytes correlated positively and highly significantly with survival to two weeks of age within individual cohorts (Brownet al., 1988). In the present study, the survival of experimental and control striped bass was monitored through the fingerling stage, under hatchery production conditions. The rate of recovery of maternally T3-treated cohorts from pond-culture was approximately fourfold that of controls. The striking effects of T3 enrichment of eggs on offspring indicate the potential contribution of maternal hormones in striped bass development, and suggest possible applications in aquaculture.

Artificial propagation of the white sturgeon, Acipenser transmontanus Richardson

Abstract The first successful reproduction of white sturgeon in captivity was conducted from February to May 1980. Ovulation and spermiation were induced in wild-caught broodstock with injections of pituitary glands from sturgeon and common carp. Eggs were incubated and hatched in MacDonald jars. Larvae and fingerlings were reared in large numbers using a variety of intensive and extensive techniques. The procedures and preliminary results of this work are described.

Gonadotropin-releasing hormone (GnRH) in bony fish that are phylogenetically ancient: Reedfish (Calamoichthys calabaricus), sturgeon (Acipenser transmontanus), and alligator gar (Lepisosteus spatula)

Three species of fish that are phylogenetically older than other members of the bony fish lineage were selected to determine if gonadotropin-releasing hormone (GnRH) is present in their brains. Brain extracts were prepared from each species and found to contain immunoreactive (ir) GnRH. To further characterize the molecular forms of GnRH in each species, the extracts were injected into a high pressure liquid chromatograph (HPLC). The elution time of each GnRH-like form was compared to those of the synthetic forms of the five known GnRHs. Several antisera were used to detect both the synthetic and unknown GnRHs in the HPLC fractions. All three species of fish had two forms of GnRH: a dominant form that is mammalian GnRH-like (mGnRH), and a minor form of irGnRH material that is similar to chicken GnRH-II (cGnRH-II). The other known forms of GnRH (salmon, lamprey, and chicken-I) were not detected. The appearance in these ancient bony fish of a mammalian-like form of GnRH, which has not been found in the jawless or cartilaginous fish studied to date, suggests that mGnRH arose in a common phylogenetic ancestor of the bony fish and tetrapods. This mGnRH-like molecule is known to have been conserved in the amphibian and mammalian lineage, but not in the reptilian or avian line. In addition, the presence of a cGnRH-II-like molecule in the bony fish examined here, and in the cartilaginous fish studied earlier, implies that this form of GnRH may have been present in an ancestor common to both of these classes of fish.

Effects of short-term management stress and ACTH injections on plasma cortisol levels in cultured white sturgeon, Acipenser transmontanus

Abstract General management practices including capture, handling and transportation in fish hatcheries can induce a stress response indicated by a plasma cortisol increase in many species. However, this phenomenon is not well established in cultured white sturgeon ( Acipenser transmontanus ). We determined resting levels of cortisol and the cortisol responses to two management stressors and to exogenous adrenocorticotropic hormone (ACTH 1–24 ) injections in cannulated mature male white sturgeon. Mean resting cortisol level was 8.6 ng/ml and ranged over 5.8–12.8 ng/ml through a 22-h period. Water reduction and transportation+handling stressors elicited significant cortisol increases above pre-stress and post-stress levels. Exogenous ACTH 1–24 injections of 0.5 and 5.0 μM caused dose-dependent peak cortisol increases above those produced by either the water reduction or transportation+handling stressors.

Dietary effects on tissue composition, oogenesis and the reproductive performance of female rainbow trout (Oncorhynchus mykiss).

Washburn, B.S., Frye, D.J., Hung, S.S.O., Doroshov, S.I. and Conte, F.S., 1990. Dietary effects on tissue composition, oogenesis and the reproductive performance of female rainbow trout (Oncorhynchus mykiss). Aquaculture, 90: 179-195. One hundred and eighty 2-year-old female rainbow trout brood&h were fed a low protein, high carbohydrate (LP), intermediate protein and carbohydrate (IP), or a high protein, low carbohydrate (HP) diet for 9 months to determine the effect of the diets on ovarian development, body proximate composition, and reproductive performance. Dietary treatment did not have any effect on the histomorphology of ovarian development. However, during vitellogenesis (July until November), fish fed different diets had significantly different body and carcass weights, plasma glucose, and plasma vitellogenin levels. Although there were some differences between the three treatments in the proximate composition of gonads, liver, and gastrointestinal tract during the reproductive cycle, no consistent pattern was seen. At spawning, LP fish retained a higher amount of lipid in the ovaries and gastrointestinal tract than the other two groups. Although the egg proximate composition was the same regardless of diet, eggs from fish fed the LP and IP diets had significantly higher survival (P-z 0.05 ) to the eye-up stage, hatchability, and relative fecundity than HP fish.

Preliminary observations on the effects of holding temperature on reproductive performance of female white sturgeon, Acipenser transmontanus Richardson

Abstract Commercial sturgeon farms in California have observed poor spawning performance and ovarian regression in fish maintained at constant 16–20°C water temperatures. The effects of the pre-spawning thermal regime on oocyte germinal vesicle migration (GVM), in vitro maturation (GVBD), plasma concentrations of reproductive hormones, and hormonally-induced ovulation in white sturgeon females were examined. Gravid females were exposed to three temperature treatments (seasonal 10–15°C, constant 15°C, and constant 18°C), and ovulation was induced when females reached the responsive stage. While all females ( n =5 per treatment) in the seasonal temperature treatment ovulated and produced fertile eggs, oocyte development (GVM) and ovulation were inhibited in the constant temperature treatments, and follicular atresia ensued in three out of five females exposed to 18°C water temperature. Temperature treatment did not have a significant effect on plasma hormone concentrations throughout the pre-spawning and spawning periods, but plasma concentrations of androgens and oestradiol declined in females that experienced developmental arrest and atresia. The spawning results provided empirical evidence for the negative effects of elevated temperatures on ovulatory response and egg quality. The pre-spawning thermal regime appears to be an important environmental factor for normal ovarian development in cultured white sturgeon and should be considered in management of wild stocks reproducing in rivers with regulated water flows.

Histology of the developing digestive system and the effect of food deprivation in larval green sturgeon (Acipenser medirostris)

Abstract The histological development of the digestive tract in hatchery-reared green sturgeon ( Acipenser medirostris ) larvae and the effects of food deprivation on the digestive system organization were studied from hatching until 31 days post-hatching (dph). At hatching, the larval digestive system consisted of two rudiments: a large endodermal yolk sac and a primordial hind-gut. During the endogenous feeding phase, the wall of the yolk sac differentiated into the stomach (glandular and non-glandular regions) and the anterior and intermediate intestine, while the hind-gut primordium differentiated into the spiral valve and rectum. At the onset of exogenous feeding (15 dph at 16 °C), the organization and cytoarchitecture of the digestive system in green sturgeon larvae was generally similar to those of juveniles and adults. Larvae deprived of food exhibited a progressive deterioration, with subtle pathological changes observed after 5-d starvation: shrinkage of digestive epithelia, tissue degeneration, and necrosis were observed at 10–15 d of starvation (30 dph). No changes were observed in the mucous secretion of different regions of the digestive tract of food-deprived larvae. The histological analysis of the larval digestive system may be used to evaluate the nutritional condition of larval green sturgeon in their nursery habitats in spawning rivers, which are affected by dams and flow diversions.