Spawning Stage Research Articles

Ultrastructural changes in the hepatocytes of juvenile rainbow trout and mature brown trout exposed to copper or zinc

AbstractMorphological changes in hepatocytes of mature brown trout (Salmo trutta Linnaeus) and juvenile rainbow trout (Salmo gairdneri Richardson), accompanying chronic exposures to copper and zinc, were examined by transmission electron microscopy. At a concentration of copper not inhibitory to the final stages of gonadal development or spawning of brown trout, structural alterations included contraction of mitochondria and a tendency for nuclei to be slightly enlarged. Concentrations of copper or zinc lethal to a small fraction (10% and 4%, respectively) of a population of juvenile rainbow trout exposed for 42 d during larval and early juvenile development caused hepatocyte changes in survivors indicative of a reduction in ability to maintain intracellular water and cation balance and possible intranuclear metal sequestering. Specific structural alterations included increased vesiculation of rough endoplasmic reticulum, an increase in the abundance of electron‐dense particles in the nucleus, increases in the numbers of multilaminar and globular inclusions, pooling of glycogen, increased autophagocytic activity and an increase in the number of necrotic cells. At advanced stages of toxicosis (concentrations of copper or zinc lethal to approximately 50% of the juveniles exposed for 42 d during development), loss in integrity of mitochondrial membranes, rupturing of plasma and nuclear membranes, separation of granular and fibrillar nuclear components, fragmentation of endoplasmic reticulum, and extensive autophagic vacuolization were significant features of hepatocytes of surviving juvenile rainbow trout.

ULTRASTRUCTURAL CHANGES IN THE HEPATOCYTES OF JUVENILE RAINBOW TROUT AND MATURE BROWN TROUT EXPOSED TO COPPER OR ZINC

Morphological changes in hepatocytes of mature brown trout (Salmo trutta Linnaeus) and juvenile rainbow trout (Salmo gairdneri Richardson), accompanying chronic exposures to copper and zinc, were examined by transmission electron microscopy. At a concentration of copper not inhibitory to the final stages of gonadal development or spawning of brown trout, structural alterations included contraction of mitochondria and a tendency for nuclei to be slightly enlarged. Concentrations of copper or zinc lethal to a small fraction (10% and 4%, respectively) of a population of juvenile rainbow trout exposed for 42 d during larval and early juvenile development caused hepatocyte changes in survivors indicative of a reduction in ability to maintain intracellular water and cation balance and possible intranuclear metal sequestering. Specific structural alterations included increased vesiculation of rough endoplasmic reticulum, an increase in the abundance of electron-dense particles in the nucleus, increases in the numbers of multilaminar and globular inclusions, pooling of glycogen, increased autophagocytic activity and an increase in the number of necrotic cells. At advanced stages of toxicosis (concentrations of copper or zinc lethal to approximately 50% of the juveniles exposed for 42 d during development), loss in integrity of mitochondrial membranes, rupturing of plasma and nuclear membranes, separation of granular and fibrillar nuclear components, fragmentation of endoplasmic reticulum, and extensive autophagic vacuolization were significant features of hepatocytes of surviving juvenile rainbow trout.

Giant choroidal cells in the lamprey eye ( Petromyzon marinus L.)

The vascular choroid of the anadromous sea lamprey eye has been examined during both the parasitic and spawning stages of these animals. It was found to be thickest at the posterior pole of the eye, where in young parasites it measures from 350 to 400 μm, while in mature spawning animals it may exceed 1 mm in thickness. The choroid is composed internally of the choriocapillaris, while large venous sinuses are restricted to the outer scleral border in younger animals but are found throughout the epichoroidal region in older spawners. Melanocytes, fibroblasts and some sparse collagen fibers are found within the choroid but the majority of this layer is filled with giant choroidal cells with diameters ranging from 60 to 75 μm. In young parasitic animals the giant choroidal cells contain large quantities of glycogen and lipid, while in mature spawning animals, the presence of these substances in minimal. These metabolic stores are often observed in close association with such cytoplasmic organelles as mitochondria and smooth endoplasmic reticulum, while pinocytotic vesicles are a common feature of the cell surface membrane, especially in older spawning animals. The functional significance of these unique glycogen-filled cells and their similarity to cells within the meninges of the lamprey central nervous system is discussed.

Ascorbic acid and the reproductive cycle of ovaries in cod ( Gadus morrhua)

1. 1. The total ascorbic acid was determined in samples from different stages of the reproductive cycle in ovaries from cod ( Gadus morrhua). 2. 2. During the early juvenile stage of development ascorbic acid showed an increase from about 150 to about 450 μg/g ovarian tissue. 3. 3. In the maturing stages the ascorbic acid decreased to about 100 μg/g at the stage of spawning. 4. 4. The findings indicate an importance of ascorbic acid in the reproductive cycle, related to growth and oogenesis.

Reproduction of Penaeus kerathurus using eyestalk ablation

In a preliminary experiment on the induction of sexual maturity in Penaeus kerathurus by unilateral eyestalk ablation, spawning was obtained in 94% of the females treated. The time necessary to reach the spawning stage appeared to be closely related to the stage of natural physiological development of the gonads and the length of the photoperiod, the period between ablation and spawning decreasing from 69 days for females treated in November to about 10 days for females treated at the beginning of their natural reproductive period in May/June. Spawning after treatment was repeated up to eight times, sometimes at intervals of less than 10 days, without showing a decrease in the amount of fertile spawn. The mean number of fertile eggs per spawn was 78.400, which is not significantly different from the corresponding mean obtained previously after thermal stimulation of almost mature breeders; the hatching percentage, 67%, was also similar. Often only the anterior and median lobes of the ovaries are included in the spawning process. The discharged spawn is nearly always completely free of matrix material. It is anticipated that induction by eyestalk ablation could allow a considerable extension of the growing season and of the area suitable for culture.

New data on the reproduction of Macrourids (Teleostei, Gadiformes)

Abstract The reproduction of deep-sea fishes is still poorly known, when it is not a total mystery. This is true in the case of those belonging to one of the most important bathybenthic families, the Macrouridae. During several research expeditions conducted by the Institut scientifique et technique des pêches maritimes aboard the oceanographic vessels Thalassa and Cryos, the stages of sexual maturity of two important species, Macrourus berglaxand Coryphaenoides rupestris, were studied. The individuals examined came from trawl catches made on the Iceland-Faroe Ridge and the Rockall and Hatton Banks in spring 1975 and 1976 and on the continental slope off the Labrador and Newfoundland coasts in summer 1975 and winter 1976. In the light of the observations made, it was possible to determine the time of spawning, especially for Coryphaenoides rupestris in the North-East Atlantic. Both males and females of this species were at the spawning stage in mid-April 1975, while a month later, they had all reached the post-spawning stage. These observations were confirmed in 1976.

Sperm Density During Active Spawning of Pacific Herring (Clupea harengus pallasi)

Discharge of milt by spawning Pacific herring (Clupea harengus pallasi) produces a milky discoloration in the water which is readily observed under favorable conditions of weather and light. Echo-sounder tracings showed that only the inshore part of a spawning school that was in contact with the bottom participated in the early stages of spawning. Sperm densities at the surface for two spawnings averaged 148 and 129 sperm/ml (range 80–210 for 16 subsamples). This density is considered more than ample for high fertilization success but is only one-tenth that normally used for artificial fertilization in the laboratory at Nanaimo.

A study of some properties of chromatin and spectrum of histones in the liver cells of spawning Oncorhynchus gorbusha (Walb.)

1. 1. The process of andromous spawing migration of the Pacific salmon O. gorbusha (Walb.) was accompanied by pronounced changes in the properties of the chromatin isolated from the liver cells. 2. 2. The chromatin from the liver of sexually mature and post-spawing animals did not precipitate in 0,3M NaCl. 3. 3. A study of the u.v.-spectrum showed the ratio E 260/E 230 to increase from 1·25 in the first stage to 1·48 in the third stage of spawning. 4. 4. The quantity of basic proteins decreased by 27 and 17% in males and females, respectively; the content of non-histone proteins by 27% in males and RNA by 50 and 40% in males and females, respectively. 5. 5. Five main fractions of histones similar to rat liver histones were revealed by electrophoresis in polyacrylamide gel of basic proteins from the liver of immature animals. 6. 6. In the liver of sexually mature animals the fraction of lysine-rich histones (F 1) disappeared. 7. 7. By the end of spawing the basic proteins of chromatins were represented by heterogenous proteins differing from typical histones in electrophoretic mobility. 8. 8. It is suggested that the changes observed are connected with enzymic degradation of the main chromatin components, particularly histones.

Identification and quantification of the major androgens in testicular and peripheral plasma of Atlantic salmon ( Salmo salar) during sexual maturation

Testicular and peripheral blood was removed from male Atlantic salmon ( Salmo salar) during two histologically distinct stages of their sexual development. Histological examination showed the earlier fish to be in an advanced maturing stage, as sperm cells at all stages of development were present in the testis lobules, and the later fish in the fully mature spawning stage. Testosterone, 11β-hydroxytestosterone and 11-ketotestosterone were quantified in the plasma by a double isotope derivative assay procedure. 11-Ketotestosterone was the major androgen in both testicular and peripheral plasma and the concentration increased substantially as maturation advanced. Testosterone levels, in peripheral plasma, remained comparatively stable but there was a trend toward increased levels in testicular plasma. The quantities of 11-ketotestosterone and testosterone were greater in the testicular than in the peripheral plasma, indicating that the testis is the primary site of their production. In addition, substantial amounts of 11-ketotestosterone, testosterone, and 11β-hydroxytestosterone were present as glucuronosides. That the concentration of glucuronosides was generally higher in testicular than peripheral plasma is direct evidence that these conjugates are produced in the testes. The concentration of 11-ketotestosterone and 11β-hydroxytestosterone glucuronosides was high in the more mature fish, but testosterone glucuronoside changed very little in concentration. 11β-Hydroxytestosterone was isolated and identified in Atlantic salmon plasma for the first time. Its concentration in testicular plasma increased in the late stages of maturation; this observation is consistent with the conclusion based on in vitro incubations that 11β-hydroxytestosterone is a precursor of 11-ketotestosterone in testis.

REPRODUCTIVE CYCLE IN CYPRINA ISLANDICA

1. The main period of gametogenesis in both sexes of Cyprina islandica occurs in late fall and early winter. In December or January the gonads of some clams present a morphologically ripe appearance, such individuals constituting approximately 20 per cent by March 15. Gametogenesis is slowed down but not entirely arrested during late winter and is resumed at a rapid rate with the spring increase in temperature.2. Spawning begins near the end of June or early in July when the water temperature is approximately 13.5° C.3. The dates when 50 per cent of the clam population should be expected to enter the stage of being ripe but not having begun to spawn, the stage of partial spawning, and the stage of completed spawning should fall within ± 3 days of June 4, August 13 and October 6 respectively.4. In adult C. islandica the sexes are separate and well defined even immediately after spawning, thus indicating that sex reversal is uncommon.5. The eggs of C. islandica cannot be artificially fertilized.