In the present study, the potential of the microalga Pavlova viridis (=Diacronema viridis) as an n-3 polyunsaturated fatty acid (PUFA) source was evaluated and compared to Nannochloropsis sp. in diets for juvenile European sea bass (Dicentrarchus labrax L.) (initial weight~12.8±1.7 g) in an 8-week feeding trial. Six different isoenergetic and isonitrogenous test diets were used: (1) fish oil diet (FO), major lipid source fish oil (100 %), (2) basal diet, 40 % fish oil and 60 % plant oil (in equal parts rapeseed, sunflower, and linseed oil), (3) Pavlova 50 % (P50), 50 % of the fish oil of the basal diet was substituted by lipid content of P. viridis meal, (4) Pavlova 100 % (P100), 100 % of the fish oil of the basal diet was substituted by lipid content of P. viridis meal, (5) Nannochloropsis 50 % (N50), 50 % of the fish oil of the basal diet was substituted by lipid content of Nannochloropsis sp. meal, and (6) Nannochloropsis 100 % (N100), 100 % of the fish oil of the basal diet was substituted by lipid content of Nannochloropsis sp. meal. The specific growth rate was highest and feed conversion ratio was lowest in the P100 group (SGR 1.77±0.10 % day −1 ; FCR 1.17±0.01), although not significantly different to the results for the FO and the other algae-groups. Furthermore, the sum of PUFA was also highest in the P100 group, followed by the P50, N100, N50, and B group (mainly due to the high content of linoleic and linolenic acids coming from plant oils and microalgal products) with the lowest levels in the FO group. The highest amounts of docosahexaenoic acid (DHA) of total fatty acids were found in the FO and B group, although not significantly higher than in groups P50 and P100. The significantly highest amount of eicosapentaenoic acid (EPA, % of total fatty acids) was in the P100 samples and the lowest amount was in samples of the basal group. The histological analyses of liver and intestine samples did not reveal any negative effects caused by the experimental treatments. Based on the basal diet, a 50 % fish oil replacement by Nannochloropsis sp. meal and a total replacement by P. viridis meal were possible without negative effects on the growth performance and nutrient utilization of juvenile sea bass.
<span>Striped mice, <em>Rhabdomys pumilio</em>, were trapped over a period of 17 months in the Thomas Baines Nature Reserve, and placed in cages, over water, until all the ticks they harboured had detached. The mice were then returned to the reserve. Four ixodid tick species were recovered from the mice of which the larvae and nymphs of <em>Rhipicephalus follis</em> and <em>Rhipicephalus simus</em> were the most numerous. Most larvae of <em>R. follis</em> detached from mice trapped from March to July, and most nymphs in March and from June to September. Most larvae of <em>R. simus</em> detached from mice trapped from December to March, and most nymphs from January to March and during May and June. Seven ixodid tick species were collected from striped mice, house rats, <em>Rattus rattus</em>, vlei rats, <em>Otomys</em> spp. and <em>Praomys</em> sp. captured in the vicinity of human dwellings or animal holding facilities in the Grahamstown district. The striped mice captured in the Thomas Baines Reserve harboured considerably larger numbers of ticks than any of the rodent species in the more urbanized localit</span>
population censuses of the main breeding population. We found that the population will continue to decline without effective intervention. Furthermore, we found that the population growth rate is most responsive to changes in survival of adult female NZSLs-the demographic group that is most threatened by fishery bycatch. Nevertheless, inferences about the efficacy of NZSL bycatch reduction measures are still imprecise. Combined, this could explain why the main population of NZSLs continues to decline. Our results emphasise that reliable data on bycatch reduction measures are needed, if they are to be shown to protect key demographic groups of marine mammals.
Gaining reliable estimates of how long fish early life stages can survive without feeding and how starvation rate and time until death are influenced by body size, temperature and species is critical to understanding processes controlling mortality in the sea. The present study is an across-species analysis of starvation-induced changes in biochemical condition in early life stages of nine marine and freshwater fishes. Data were compiled on changes in body size (dry weight, DW) and biochemical condition (standardized RNA-DNA ratio, sRD) throughout the course of starvation of yolk-sac and feeding larvae and juveniles in the laboratory. In all cases, the mean biochemical condition of groups decreased exponentially with starvation time, regardless of initial condition and endogenous yolk reserves. A starvation rate for individuals was estimated from discrete 75th percentiles of sampled populations versus time (degree-days, Dd). The 10th percentile of sRD successfully approximated the lowest, life-stage-specific biochemical condition (the edge of death). Temperature could explain 59% of the variability in time to death whereas DW had no effect. Species and life-stage-specific differences in starvation parameters suggest selective adaptation to food deprivation. Previously published, interspecific functions predicting the relationship between growth rate and sRD in feeding fish larvae do not apply to individuals experiencing prolonged food deprivation. Starvation rate, edge of death, and time to death are viable proxies for the physiological processes under food deprivation of individual fish pre-recruits in the laboratory and provide useful metrics for research on the role of starvation in the sea.
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