Weeks In Freshwater Research Articles

Changes in plasma growth hormone and various metabolic factors during smoltification of coho salmon, Oncorhynchus kisutch

Plasma and tissue samples were collected weekly from juvenile coho salmon during the parr-smolt transformation as well as for an additional 12 weeks in freshwater during desmoltification. The parameters measured were: plasma growth hormone, muscle glycogen, liver glycogen, liver glucose, muscle protein, muscle amino acid nitrogen, and individual plasma saturated and unsaturated free fatty acids. Plasma levels of growth hormone increased over the sampling period. Muscle and liver glycogen decreased during smoltification but increased again over desmoltification. Liver free glucose was unchanged over the sampling period except for low levels seen over a 3-week period immediately following normal release from the hatchery. The ratio of liver free glucose to glycogen increased during smoltification and then decreased. Muscle protein levels were fairly stable over both smoltification and desmoltification. Amino acid nitrogen content of the muscle fluctuated weekly but generally increased over the latter weeks of the study. Both the saturated and unsaturated plasma free fatty acids remained stable initially, but increased dramatically near the end of the study. Correlations between the various parameters and plasma growth hormone are examined to ascertain possible roles of growth hormone in the physiology of the smoltification and desmoltification processes.

Effects of dietary trimethylamine on the concentration of trimethylamine oxide in various tissues of the chum salmon, Oncorhynchus keta, in freshwater and sea-water environments

1. 1. Young chum salmon were given one or other of three diets that differed in TMA contents for 4 weeks in freshwater and for 3 weeks in sea-water after 2 weeks adaptation for sea-water. 2. 2. The growth of fish fed on the TMA I diet (TMA 17 mg/100 g) was greater than that of fish fed on the TMA II diet (TMA 171 mg/100 g). 3. 3. TMA and TMO concentrations in the various tissues of the fish were determined. The concentrations of TMA and TMO in the various tissues were influenced by the dietary TMA level and environmental sea-water. 4. 4. The freshwater, fish fed on the TMA I diet had higher TMA and TMO levels in the whole body, muscle and kidney than fish fed on the basal diet or the TMA II diet. 5. 5. Also, in sea-water, the TMA I diet enhanced the accumulation of TMA and TMO in the whole body, muscle, liver and kidney. 6. 6. The levels of TMO in the tissues such as the liver and kidney were increased by feeding TMA I diet, and those increases were higher in sea-water than in the freshwater environment. 7. 7. NPN levels in either freshwater or sea-water fish did not differ greatly between the diets. Except for the whole body and muscle slightly higher values were found in sea-water than in freshwater fish.

Electrolyte balance in hypophysectomized goldfish, Carassius auratus L

Hypophysectomized goldfish ( Carassius auratus L.) kept for 3 weeks in fresh water show a sharp decrease (35% or more) in plasma Na and Cl concentrations. Due to expansion of the apparent Na space, however, total exchangeable Na drops only about 20%. Flux analyses, using 22Na, show that hypophysectomized fish are in strongly negative Na balance. Urinary Na concentration rises but urine flow decreases to about 55% of normal. The rate of urinary Na loss is not significantly greater than that of intact or sham-operated fish. Negative Na balance is thus due to increased extrarenal Na loss. Repeated injections of sheep prolactin partially prevent the decline in plasma electrolyte concentrations. ACTH injections are ineffective in this respect. Survival of hypophysectomized goldfish in fresh water for long periods appears to be due largely to their ability to withstand dilution of the internal medium.

A bioassay for fish prolactin (paralactin)

A procedure is described for assay of the content of fish prolactin (paralactin) in pituitary homogenates, in which the end-point is the elevation of plasma sodium induced by the hormone in hypophysectomized Poecilia latipinna in freshwater. Plasma sodium level in this procedure is linearly related to log dose of three sources of prolactin (1) ovine prolactin (standard) and, in parallel, homogenates of (2) frog pars distalis and (3) P. latipinna pituitary. The assay is statistically satisfactory, with a good index of precision (mean λ for 5 assays was 0.07, range 0.06–0.08). Application of the assay to P. latipinna pituitary homogenates showed that the fish prolactin content of the pituitary gland doubled during the 72 hours after transfer from dilute seawater to freshwater, and was still elevated after 4 weeks in freshwater. The assay was also used to determine the prolactin content in female frog ( Rona teniporaria) pars distalis.

Studies on Angiostrongylus cantonensis in Molluscan Intermediate Hosts

First-stage larvae of Angiostrongylus cantonensis from rat feces developed to infective third-stage larvae in 20 of 26 species of freshwater mollusks experimentally exposed. Numbers of larvae up to 2,000 per snail and survival of larvae for a year were observed in Biomphalaria glabrata. First-stage larvae were susceptible to drying but survived at least 3 weeks in freshwater and were infective to snails after at least 2 weeks in either freshwater or seawater. B. glabrata was routinely infected by ingestion of infected rat feces, and first-stage larvae were observed penetrating the wall of the intestine. A cellular reaction enclosed the developing larvae in tissue nodules. Isolated third-stage larvae were susceptible to drying but survived up to 11 days in B. glabrata removed from water, larvae remaining alive 4 days after death of the snails. Rats became infected by drinking water containing third-stage larvae, and larvae were observed active in freshwater for up to a week. Infected B. glabrata died a few minutes after immersion in seawater, but yielded by digestion numerous infective larvae after 4 days in seawater, and a few infective larvae after 5 days. Results suggest the potential importance of freshwater mollusks as intermediate hosts and the possibility of infection of marine hosts. The life cycle of Angiostrongylus cantonensis (Chen) Dougherty, the rat lungworm, was described by Mackerras and Sandars (1955). A. cantonensis has been suspected as the etiologic agent of eosinophilic meningoencephalitis in several Pacific Islands (Rosen et al., 1961, 1962; Horio and Alicata, 1961; Alicata, 1962a, 1962b; and Alicata and Brown, 1962). Human infections were reviewed by Rosen et al. (1962); by Weinstein et al. (1963); and by Kuntz and Myers (1964). Terrestrial mollusks, both slugs and snails, have been infected (Mackerras and Sandars, 1955; Weinstein et al., 1962; and Alicata, 1962a). Experimental infection of the freshwater snail Fossaria ollula was reported by Alicata and Brown (1962). Liat et al. (1965) found three species of freshwater snails infected in nature with A.

The ultrastructure of the eel pituitary at the elver stage with special reference to its neurosecretory innervation.

The present study deals with the development of the pituitary of the eel at the following stages: immediately after the elvers have left their marine environment and after 8 and 16 weeks in freshwater. The following results have been obtained: 1. The pars nervosa of the neuro-intermediate lobe of elvers is highly differentiated. As in adult eels, 3 types of neurosecretory fibre can be distinguished (A1 fibres: size of granules c. 1700 A; A2 fibres: c. 1200 A; B fibres: c. 750 A) and synapses between A2 fibres and pituicytes are present. 2. In the pars intermedia, 3 types of cell are present (type I, II and III). Type I and type III cells show striking changes which appear to be consistent with the view that type I cells are involved in production of MSH and that type III cells are affected by osmotic changes. 3. Already in elvers of stage I, the nerve tracts innervating the pars distalis contain an abundance of type B neurosecretory fibres and a small amount of type A fibres. In elvers of stage II, type A neurosecretion has increased and can be demonstrated also by light microscopy. 4. In the proximal pars distalis of elvers of stage I only STH cells and a few undifferentiated cells are present. In the following stages the latter ones appear to have been transformed into gonadotrophic cells. 5. In the rostral pars distalis of all stages investigated ACTH, TSH, and ‘prolactin’ cells are present. In elvers of stage I, at the level of ultrastructure, TSH cells can be demonstrated in abundance but not all of them have developed their typical staining pattern. In elvers of stage II the differentiation of the TSH cells appears to be finished. ‘Prolactin’ cells are relatively undifferentiated in elvers of stage I but are well developed and show signs of great activity in elvers of stage III. These observations are discussed in view of the possible role of a prolactin-like hormone for the adaptation to freshwater. 6. The development of intervascular channels which link neurosecretory tracts and endocrine cells is described and the possible role of neurosecretion for the function of pars distalis cells is discussed.