A series of experiments were conducted to determine the toxicity, behavior, blood glucose stress response, and disease susceptibility in Nile tilapia Oreochromis niloticus following un‐ionized ammonia (UIA) exposure. The acute toxicity of un‐ionized ammonia to Nile tilapia was measured in a 96‐h static test. The median lethal concentration (LC50) was 1.46 mg/L UIA at 24 and 48 h postexposure, 1.33 mg/L at 72 h postexposure, and 0.98 mg/L at 96 h postexposure. No mortalities were noted in unexposed (0 mg/L) control fish or fish exposed to 0.5 mg/L UIA. However, 93–100% mortalities were observed within 24 h among fish exposed to 2.0, 3.0, or 4.0 mg/L UIA. In additional UIA exposure experiments, Nile tilapia were exposed to sublethal concentrations (0.32–0.37 mg/L UIA) for 24 h and then administered an intraperitoneal injection with 750 colony‐forming units (CFU) of Streptococcus agalactiae per fish. Mortalities of UIA‐exposed and control fish were not significantly different 21 d postchallenge. Blood glucose levels were not significantly different between exposed and control fish 24 h after the beginning of UIA exposure or between preexposure fish and 24‐h postexposure fish. Glucose levels in both groups increased significantly after UIA exposure and subsequent bacterial challenge, suggesting that Nile tilapia experienced handling or infection stress and not necessarily UIA exposure stress alone. During a time course study with 24‐h UIA exposure, sequential blood glucose samples indicated acute stress responses 1–4 h postexposure that decreased by 24 h postexposure. The results of this study indicate that exposure to increased UIA concentrations alone had acute, transient effects on stress responses in Nile tilapia and that 24‐h exposure to sublethal UIA concentrations up to 0.37 mg/L did not increase susceptibility to S. agalactiae.
Summary Clove oil can be used as an anaesthetic in the handling of marine and freshwater fish. Few studies report on its use for periods up to 48 h, for example, under long‐distance transport conditions. This study tested the effect of different clove oil concentrations for 1–48 h on recovery and survival of the cichlid Haplochromis obliquidens, an ornamental fish species endemic to Lake Victoria. Haplochromis obliquidens were anaesthetized for 1 h using 5–25 μl L−1 clove oil. There was no correlation between clove oil concentration and post‐anaesthesia recovery time (P = 0.15). On average, fish recovered within 9.5 ± 2 min, and no fish died within 24 h after recovery. Results from exposure of fish to 18–20 μl L−1 clove oil for up to 48 h suggested a narrow margin of safety as this concentration range induced mortality. At 18 μl L−1 recovery times ranged from 3 to 43 min between 24 and 36 h exposure, while fish exposed longer than 36 h recovered within 1–10 min, or within 1–2 min after 44–48 h. At the end of a 48‐h transport experiment total ammonia levels were higher in transport water containing anaesthetized fish than for non‐anaesthetized fish (1.65 ± 0.19 and 0.54 ± 0.08 mg L−1 NH + NH3, respectively). The combined use of clove oil and the selective ammonium ion exchanger zeolite was considered feasible as ammonia levels could be reduced by up to 82% compared to control bags without zeolite.
Illegal fishing activities are reported to be on the increase in South Africa, including in its marine protected areas (MPAs). Research is presented on the nature and the scale of illegal fishing in Table Mountain National Park (TMNP) by analysing the numbers of abalone Haliotis midae and West Coast rock lobster Jasus lalandii confiscated from fishers operating in the park's marine protected area between 2000 and 2009. Data were collected from offence logbooks maintained by South African National Parks rangers and managers, the South African Police Services, and interviews with alleged or self-confessed illegal fishers. The research findings indicate that the annual numbers of illegally fished abalone and rock lobsters have increased significantly over time. Spatial analysis suggests that confiscations of abalone occur predominantly on the east coast of the park, whereas higher confiscations of illegally fished rock lobsters occur on the west coast. It is clear from this research that new and more efficient approaches will need to be designed and implemented to minimise illegal fishing in the TMNP MPA. Contextspecific conservation targets that acknowledge and integrate social as well as developmental needs are required, and may be essential for limiting biodiversity loss in the longer term, which will ultimately ensure the success of fisheries management and conservation in TMNP.
Harvesting of non-timber forest products is an integral component of rural livelihoods throughout the developing world. At times this is at odds with conservation objectives. Reconciliation of the two requires examination of local level contexts and needs. This paper reports on the harvesting needs for Ischyrolepis by a rural community in South Africa, against the setting that they had recently been prohibited from harvesting by the local conservation officials. Interviews were conducted with conservation officials to understand the reasoning for the prohibition. Local demand for Ischyrolepis was assessed by household surveys, as well as in-depth interviews with traders. The density and size class distribution of Ischyrolepis was determined using transects. The total annual demand for Ischyrolepis was determined to be approximately only 2.7% of the standing crop. The bulk of the annual demand was for small-scale trade, the income from which was a primary source of income for the few harvesters. Very little evidence could be found indicating that harvesting was damaging the resource or its habitat, and local knowledge suggested that the abundance of the species was stimulated by harvesting. Even if market demand were to increase, the size of the shoots required means that less than 20% of the standing crop could be harvested annually. Current regulations around harvesting are in a state of revision, and hence confusion prevails regarding if harvesting is permissible, and if so, under what conditions, which is detrimental to both conservation and livelihoods.
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