Condition-dependent responses of fish to motorboats.

Anthropogenic noise is a pollutant of global concern that has been shown to have a wide range of detrimental effects on multiple taxa. However, most noise studies to-date consider only overall population means, ignoring the potential for intraspecific variation in responses. Here, we used field experiments on Australia's Great Barrier Reef to assess condition-dependent responses of blue-green damselfish (Chromis viridis) to real motorboats. Despite finding no effect of motorboats on a physiological measure (opercular beat rate; OBR), we found a condition-dependent effect on anti-predator behaviour. In ambient conditions, startle responses to a looming stimulus were equivalent for relatively poor- and good-condition fish, but when motorboats were passing, poorer-condition fish startled at significantly shorter distances to the looming stimulus than better-condition fish. This greater susceptibility to motorboats in poorer-condition fish may be the result of generally more elevated stress levels, as poorer-condition fish had a higher pre-testing OBR than those in better condition. Considering intraspecific variation in responses is important to avoid misrepresenting potential effects of anthropogenic noise and to ensure the best management and mitigation of this pervasive pollutant.

Fishes in a changing world: learning from the past to promote sustainability of fish populations.

Populations of fishes provide valuable services for billions of people, but face diverse and interacting threats that jeopardize their sustainability. Human population growth and intensifying resource use for food, water, energy and goods are compromising fish populations through a variety of mechanisms, including overfishing, habitat degradation and declines in water quality. The important challenges raised by these issues have been recognized and have led to considerable advances over past decades in managing and mitigating threats to fishes worldwide. In this review, we identify the major threats faced by fish populations alongside recent advances that are helping to address these issues. There are very significant efforts worldwide directed towards ensuring a sustainable future for the world's fishes and fisheries and those who rely on them. Although considerable challenges remain, by drawing attention to successful mitigation of threats to fish and fisheries we hope to provide the encouragement and direction that will allow these challenges to be overcome in the future.

Spermatogenesis and synaptonemal complexes of hybrid Petrogale (Marsupialia).

Fertility, synaptonemal complexes (SCs) and spermiogenesis were examined in hybrids bred from four chromosomally different species of rock wallaby. Each of the four male hybrids had different forms of chromosomal heterozygosity (i.e., a trivalent, a quadrivalent, a pentavalent, and a trivalent plus two centric shifts). Testes and seminiferous tubules of each hybrid were smaller than those of full-bloods, and no hybrid produced young when paired with parous females. The degree of chromosomal heterozygosity in the hybrids was associated with the degrees of asynapsis, XY-autosome associations, and disruption of spermatogenesis. In only one hybrid were all stages of spermiogenesis commonly seen, and in this animal, sperm abnormalities were common. SC formation was consistent with that expected from the G-banded karyotypes, except that in one hybrid the chromosomes involved in the presumed centric shifts did not pair as expected but instead formed heteropycnotic masses. In addition, the studies demonstrated the links between the nonpairing X and Y chromosome and revealed an array of patterns of abnormalities at the ultrastructural level in spermiogenesis of hybrid marsupials.

Glucocorticoid/antiinflammatory activities of nonsteroidal phenylpyrazoles in the rat.

Six nonsteroidal phenylpyrazoles are described that have significant glucocorticoid and antiinflammatory activities. These agents competed with dexamethasone for the glucocorticoid receptor from the rat thymus, suppressed adrenal weight when administered orally to intact female rats, produced liver glycogen deposition and thymolysis when administered orally to adrenalectomized male rats, and reduced cotton granuloma formation when administered in the cotton pellet. In addition, in the latter model, no systemic activity (thymolysis or reduced body weight gain) was seen with doses up to 500 to 5000 times the dose which reduced granuloma formation. At least one compound was more potent than methylprednisolone in three of the four rat assay systems used. The compounds described are structurally different from conventional steroidal glucocorticoids but possessed potent glucocorticoid activities. However, they exhibited antiinflammatory activity without evidence of systemic activity when administered locally.

Inhibition of furosemide-induced kaliuresis in the rat by trilostane, an inhibitor of adrenal steroidogenesis.

In rats treated with furosemide, urinary losses of water, sodium and potassium were accompanied by increased circulating levels of aldosterone. Trilostane, an inhibitor of adrenal 3 beta-hydroxysteroid dehydrogenase activity, prevented furosemide-induced hyperaldosteronism which resulted in a partial inhibition of diuretic-induced kaliuresis without a change in sodium and water excretion. Spironolactone, an antagonist of mineralocorticoid action with inherent diuretic activity, produced qualitatively similar effects to those of trilostane on urinary electrolyte excretion in furosemide-treated intact rats. However, mineralocorticoid-induced potassium loss in adrenalectomized rats was not altered by trilostane but was prevented by spironolactone reflecting the direct effect of spironolactone on the kidney. In addition, furosemide-induced kaliuresis in adrenalectomized rats was not prevented by trilostane. Therefore, although both trilostane and spironolactone reduce diuretic-induced potassium loss, spironolactone acts by competing with aldosterone for the mineralocorticoid receptor while trilostane appears to act exclusively by preventing secondary hyperaldosteronism.

Nivazol: a glucocorticoid in rats with only hypothalamic-pituitary-adrenal-inhibiting activity in primates.

The synthetic steroid nivazol lacks three of the substituents considered to be important for glucocorticoid activity, i.e. the 3-keto, the 11-hydroxy, and the 20-keto groups. Nevertheless, in the rat, nivazol has the activity profile of a glucocorticoid. After treatment of intact female rats with nivazol , the mean weights of the adrenals and thymus were lower than those in the vehicle-treated control group. The results were qualitatively and quantitatively similar to those obtained with methylprednisolone. Thymolysis as well as liver glycogen deposition were seen in adrenalectomized rats treated with nivazol , and eosinopenia and inhibition of carrageenan edema were noted in intact rats. In the rhesus monkey, treatment with nivazol resulted in a marked reduction in circulating cortisol levels and elimination of the diurnal pattern, although a dose 10 times that needed to reduce circulating cortisol levels did not produce eosinopenia or increase fasting blood glucose levels. Both eosinopenia and higher fasting blood glucose levels were seen after treatment with methylprednisolone. Nivazol did not prevent the ACTH-induced increase in circulating cortisol levels nor did it alter circulating aldosterone levels. Therefore, suppression of ACTH is the predominant if not the sole action of nivazol in the primate. Preliminary results in clinical trials suggest a similar activity profile in humans. Therefore, nivazol elicits numerous glucocorticoid activities in the rodent, but only the inhibition of the hypothalamic-pituitary-adrenal axis was observed in the primate. It is of special interest that the inhibition of the hypothalamic-pituitary-adrenal axis occurs without altering circulating aldosterone levels and without evidence of debilitating catabolic activity.

Crystalloid inclusions in the Sertoli cell of the koala, Phascolarctos cinereus (Marsupialia).

Crystalloid inclusions are a common feature in the basal region of Sertoli cells in the koala, Phascolarctos cinereus. Generally located near the nucleus, they are non membrane-bounded, slender rectangular structures composed to tubules which are orientated at right angles to the long axis of the crystalloid and regularly arranged in rows parallel to this long axis. The tubules in adjacent rows are offset from one another at definite angles and extensively interconnected by filaments. Neither the composition nor function of the crystalloids has been determined, but their association with tonofilaments and the presence of ribosomes in the vicinity suggests that they are most likely proteinaceous.

(exo, exo)-2-Aryltropane-3-carboxylic esters, hypoglycemic agents with accompanying analgesic activity.

(exo, exo)-2-Aryltropane-3-carboxylic esters of types 6, 7, and 10 lower circulating blood glucose levels by 60--80%. This activity is accompanied by an analgesic activity roughly equal to that of codeine. Both of these activities reside in the 1R enantiomer and extensive structure-activity studies failed to separate them. The specific opioid antagonist nalorphine blocks the analgesic activity but does not diminish the hypoglycemic action. Conformational integrity afforded by the ethylene bridge is neccessary for the observed activities.

Ultrastructural changes in spermatozoa of the brush-tailed possum, Trichosurus vulpecula (Marsupialia), during epididymal transit. Part II: The acrosome.

The acrosome in spermatozoa from the caput epididymidis of the Australian Brush-tailed possum, Trichosurus vulpecula, typically forms a cup-like structure, sitting on the anterior third of the dorsal surface of the nucleus. The base of the acrosomal 'cup' is narrowly separated from the nuclear surface, while the body of the 'cup' projects voluminously away from the nucleus. During epididymal transit these pronounced marginal extensions of the acrosome are retracted towards the nucleus, and the electron dense acrosomal material undergoes a process of compaction within the plasma membrane of the head to produce the convex ovate form of the definitive acrosome. During this process a variety of bizarre forms of the acrosome are produced before its final configuration is attained.

Spermiogenesis in the brush-tailed possum, Trichosurus vulpecula (Marsupialia). The development of the acrosome.

Acrosome development in the Australian Brush-tailed possum, Trichosurus vulpecula, displays a number of extraordinary features. This is particularly evident in the later stages of spermiogenesis, when the area of the nuclear surface bounded by the nuclear ring, and covered by the acrosome, is reduced considerable. As a result, the acrosomal material becomes located over its definitive position on the anterior third of the dorsal nuclear surface; in this process it is thrown into a series of folds, and a wide subacrosomal space is formed. Further changes around the time of spermiation result in the release of a spermatozoon in which a thin layer of acrosomal material is closely applied to the nucleus over the area of the definitive location of the acrosome, whilst its margins are greatly extended and project freely away from the nucleus. The latter feature does not appear to have been reported for the sperm of other mammals.

Ultrastructural changes in spermatozoa of the brush-tailed possum, Trichosurus vulpecula (Marsupialia), during epididymal transit. Part I: The flagellum.

During epididymal transit, a fibre network and an array of vesicles develop in the posterior two-thirds of the midpiece in sperm of the Brush-tailed possum, Trichosurus vulpecula. The fibre network is developed by the time the sperm reach the corpus epididymidis, and is composed of evenly spaced, helically arranged fibres lying immediately beneath the plasma membrane. The angle of these fibrous helices is always counter to that of the underlying mitochondrial helix. Separating the fibre network from the mitochondria is a layer of granular material which develops at the same time, and over the same length of the midpiece as the fibre network. A somewhat tenuous fibre network is found between the fibrous sheath and plasma membrane in the anterior principal piece of sperm from all regions of the epididymis. The array of vesicles is developed by the time sperm reach the cauda epididymidis. The vesicles resemble pinocytotic vesicles; some appear as invaginations of the plasma membrane, and are open to the medium surrounding the spermatozoon by a narrow neck, while others are entirely enclosed within the spermatozoon, and lie at varying distances between the plasma membrane and the layer of granular material.