Maximal activities of enzymes involved in adenosine metabolism in muscle and adipose tissue of rats under conditions of variations in insulin sensitivity

The maximal activities of 5'-nucleotidase, adenosine deaminase and adenosine kinase were measured in quadriceps or soleus muscle from animals in which the sensitivity to insulin was changed. Most conditions caused no effect on the activities but exercise-training increased the activity of adenosine deaminase and cold exposure increased the activity of 5'-nucleotidase in soleus muscle: in addition, ageing decreased markedly the activities of all three enzymes in both muscles. When the activities are based on mg protein they are much higher in both white and brown adipose tissue than in muscle, suggesting that changes in adenosine concentration may be important in changing insulin sensitivity in adipose tissue whereas changes in adenosine receptor number may be more important in muscle.     

The relation between daily rings, body growth and environmental factors in plaice, Pleuronectes platessa L., juvenile otoliths

The deposition rate of sagittal otolith rings in post-metamorphosed plaice, Pleuronectes platessa , was considered in relation to body growth under three feeding levels and two photoperiod regimes. Feeding levels and photoperiods significantly influenced the number of rings; more rings were deposited at higher levels of feeding and in longer photoperiod regimes. There was also a linear relationship between fish growth and the number of rings. The results suggest that sagittal rings could be used for aging wild juvenile plaice during the period of the growing season when growth rate is greater than 0.1 mm day¹.     

An experimental study of phytoplankton feeding in three tilapiine cichlids

Three species of tilapia ( Oreochromis lidole, O. karongae and O. niloticus ) were fed on four planktonic algal diets in the laboratory. The algal concentrations were measured over a 24-h period and the ingestion rates calculated. In monocultures of large algae (average filament length=477 μm) O. niloticus had the highest ingestion rate, but on small algae (particle size <8 μm) O. lidole was the fastest, while O. karongae enhanced nanoplankton production. With algae of mixed sizes, O. niloticus was able to remove small algae quicker than the other fish species. Thus, the presence of larger algae can influence the impact of a planktivorous species on nanoplankton. O. lidole is likely to have the greatest impact on plankton communities heavily dominated by smaller algae.     

Desensitization of the isolated beta 2-adrenergic receptor by beta-adrenergic receptor kinase, cAMP-dependent protein kinase, and protein kinase C occurs via distinct molecular mechanisms.

Exposure of beta 2-adrenergic receptors (beta 2ARs) to agonists causes a rapid desensitization of the receptor-stimulated adenylyl cyclase response. Phosphorylation of the beta 2AR by several distinct kinases plays an important role in this desensitization phenomenon. In this study, we have utilized purified hamster lung beta 2AR and stimulatory guanine nucleotide binding regulatory protein (Gs), reconstituted in phospholipid vesicles, to investigate the molecular properties of this desensitization response. Purified hamster beta 2AR was phosphorylated by cAMP-dependent protein kinase (PKA), protein kinase C (PKC), or beta AR kinase (beta ARK), and receptor function was determined by measuring the beta 2AR-agonist-promoted Gs-associated GTPase activity. At physiological concentrations of Mg2+ (less than 1 mM), receptor phosphorylation inhibited coupling to Gs by 60% (PKA), 40% (PKC), and 30% (beta ARK). The desensitizing effect of phosphorylation was, however, greatly diminished when assays were performed at concentrations of Mg2+ sufficient to promote receptor-independent activation of Gs (greater than 5 mM). Addition of retinal arrestin, the light transduction component involved in the attenuation of rhodopsin function, did not enhance the uncoupling effect of beta ARK phosphorylation of beta 2AR when assayed in the presence of 0.3 mM free Mg2+. At concentrations of Mg2+ ranging between 0.5 and 5.0 mM, however, significant potentiation of beta ARK-mediated desensitization was observed upon arrestin addition. At a free Mg2+ concentration of 5 mM, arrestin did not potentiate the inhibition of receptor function observed on PKA or PKC phosphorylation. These results suggest that distinct pathways of desensitization exist for the receptor phosphorylated either by PKA or PKC or alternatively by beta ARK.     

Age determination and growth of the pollan, Coregonus autumnalis pollan Thompson, of Lough Neagh, Northern Ireland

Scales from Lough Neagh pollan display a large number of checks, making age determination difficult. Sclerite counts showed that an annual check is formed on scales in May and a second accessory check in most young fish in October. The method of ageing from scales was supported by inspection of length-frequency plots and by following the growth of pollan in their first 2 years of life. The body-scale relationship was curvilinear. Back-calculation showed that pollan of both sexes attain a fork length of 29 cm in 5 years (1 ∞=28.9 cm; k = 0.65; l ₀= -0.06 year). There is no evidence that annual growth rates have changed since 1965. Possible environmental causes of scale check formation are discussed.     

Genetic quality and offspring performance in Chinook salmon: implications for supportive breeding

Each year salmon and other fishes are caught and used for supportive breeding programs that attempt to augment natural populations that are threatened with extinction. These programs typically mate individuals randomly and as such they overlook the importance of genetic quality to offspring fitness and ultimately to ensuring population health. Here, we use Chinook salmon (Oncorhynchus tshawytscha) and a fully crossed quantitative genetic breeding design to partition genetic variance in offspring performance (growth and survival) to additive and non-additive genetic effects as well as maternal effects. We show that these three effects contribute about equally to the variation in survival, but only non-additive genetic and maternal effects contribute to variation in growth. Some of the genetic effects could be assigned to variation at the class IIB locus of the major histocompatibility complex, but the maternal effects were not associated with egg size and we found no relationship between dam phenotypic measures and offspring survival or growth. We also found no relationship between sire sexually selected characters and offspring survival or growth, which is inconsistent with a “good genes” hypothesis. Finally, we show that incorporation of genetic quality into supportive breeding programs can increase offspring growth or survival by between 3% and 19% during the endogenous feeding stage alone, and projections to adulthood suggest that survivorship could be over four fold higher. Electronic Supplementary Material  Supplementary material is available in the online version of this article at and is accessible for authorised users.