To migrate, or not to migrate: partial diel horizontal migration of fish in a temperate freshwater reservoir

The diel horizontal migration (DHM) of fish between the inshore and offshore zones of the ?ímov Reservoir (Czech Republic, deep, stratified, meso-eutrophic) was investigated by a combination of horizontal and vertical hydroacoustic surveys at 3-h intervals over 48 h and day/night purse seining in August 2007. An overwhelming majority of fish were aggregated within the epilimnetic layer. Considering only the horizontal surveys, cyclic diel fish movements between inshore and offshore habitats were apparent, while the total fish biomass remained constant between day and night. A higher fish biomass was detected in the offshore zone during daytime by both hydroacoustics and purse seining. In contrast, a higher fish biomass was recorded at night in the inshore zone. Bream Abramis brama, roach Rutilus rutilus, and perch Perca fluviatilis dominated the daytime offshore fish assemblage whereas bleak Alburnus alburnus prevailed at night. Bream and roach decreased in abundance at night while perch completely disappeared from the offshore habitat. The diel differences in size distributions and direct catches suggested the population-wide horizontal offshore migration of bleak and inshore migration of all perch during dusk. On the other hand, partial inshore migration of bream and roach adults was observed during dusk (52 and 80%, respectively). The different proportions of offshore residents among species and size classes suggested that differences in size, and, therefore, predation vulnerability, contributed to the observed migration patterns.     

To breed or not to breed: Physiological correlates of reproductive status in a facultatively biennial iguanid

It is unusual for seasonal breeders to frequently skip opportunities for reproduction. We investigated the relationship between physiological state and reproductive decision-making in Galápagos marine iguanas (Amblyrhynchus cristatus), a species in which females typically reproduce biennially, although the proportion of breeding individuals varies significantly across years. Nearly all adult-sized females initiated follicular development prior to the lekking period, but 38% of females resorbed all developing follicles 5-15 days before the start of copulations. Receptive and non-receptive females differed in reproductive hormones during the mate choice period. Testosterone peaked in receptive females immediately prior to copulation, indicating that testosterone or its derivative estradiol likely mediates female receptivity in Galápagos marine iguanas. Non-receptive females showed significant peaks in both testosterone and progesterone during follicular atresia, suggesting that these hormones may be involved in inhibiting vitellogenesis. Two to three weeks prior to the period of reproductive decision-making (and the onset of follicular atresia in non-receptive females) receptive females were in higher body condition, were developing larger follicles, and had lower levels of both baseline and stress-induced corticosterone. Reproduction is extremely costly in this long-lived species, and increases the likelihood of mortality in the year following breeding; females could therefore gain significant benefits from being attuned to indicators of reproductive success. We suggest that corticosterone may modulate reproductive decisions by altering individual sensitivity to both internal and external cues of the likelihood of successful reproduction.     

To treat or not to treat: a quantitative review of the effect of biofouling and control methods in shellfish aquaculture to evaluate the necessity of removal

The global growth of farmed shellfish production has resulted in considerable research investigating how biofouling compromises farm productivity. Shellfish fitness can be compared between fouled stock and stock which has undergone treatment. As treatment options are often harsh, they may deleteriously affect stock. The projected impact of biofouling may therefore be confounded by the impact of treatments. Given the substantial cost of fouling removal, some have questioned the necessity of biofouling mitigation strategies. Meta-analysis revealed that biofouling typically reduces shellfish fitness. However, the fitness of treated stock was often lower or equal to fouled control stock, indicating that many common antifouling (AF) strategies are ineffective at enhancing farm productivity. Overall, caution and diligence are required to successfully implement biofouling mitigation strategies. The need remains for increased passive prevention approaches and novel AF strategies suitable for shellfish culture, such as strategic siting of bivalve farms in areas of low biofouling larval supply.     

Exposure to female pheromones stimulates a specific type of neuronal population in the male but not female magnocellular division of the medial preoptic nucleus (MPN mag) of the Syrian hamster

The magnocellular division of the medial preoptic area (MPN mag) integrates pheromonal and hormonal signals to play a critical role in the expression of male typical sex behavior. The MPN mag contains two morphologically distinct neuronal populations; the percentage of each type within the nucleus is sex specific. Males have more neurons with a single nucleolus whereas females have more with multiple nucleoli. To determine which neuronal subtype mediates pheromonal induction of copulation, tissue from male and female hamsters exposed to female pheromones was immunolabeled for the immediate early protein (EGR-1). Subsequently the tissue was counterstained and the number of ERG-1 neurons with one or two nuclei was determined. The results indicate that pheromones stimulate neurons with single nucleoli in males but fail to stimulate either neuronal subtype in females suggesting that synaptic input to the MPN mag is sexually differentiated.