Human Food Safety and Environmental Assessment of the Use of 17α-Methyltestosterone to Produce Male Tilapia in the United States

Sex reversal of early life stage tilapia (approximately 7–12 d post-hatch, total length averaging 9–11 mm, and total weight averaging 10–15 mg) is used commonly to produce populations of fish comprised of > 5% phenotypic females. The synthetic androgen, 17α-methyl testosterone (MT), is used to effect sex reversal in tilapia. This paper evaluates environmental impact and human food safety aspects of MT use for tilapia sex reversal based on a review of the scientific literature and on dilution models of farm discharge.
Effect of MT treatment on human food safety was evaluated by regression analysis of radioactivity depletion data and by dilution through growth analysis. Results show that the proposed use of MT for sex reversal of early life stage tilapia presents no negative effects on human food safety. Regression analysis of available depletion data from tilapia shows that whole-body concentrations of MT and metabolites in tilapia attain levels of <100 pg/g after 8 to 40 d of withdrawal, and that achievement of <10 pg/g of MT and metabolites in carcass tissue occurs after 6 to 50 d of withdrawal. These concentrations are attained well before completion of the FDA-required 120-d withdrawal period following MT treatment.
Standardized calculations were made to estimate MT concentration in effluents based on stocking rate and water exchange. Guidelines are provided for management of farms to ensure that effluent MT concentration remains < 1 μg/L. Given the expected concentration of MT in any farm effluents, the rapid dilution of effluent MT to very low levels in receiving waters, the sensitivity of MT to photo-oxidation, the expected rapid bacterial degradation of MT, and the limited total use of MT in the United States, we concluded that the use of MT-treated feed according to the proposed protocol will not cause significant adverse environmental effects.     

Influence of marine reserve size and boundary length on the initial response of exploited reef fishes in the Florida Keys National Marine Sanctuary,USA

We examine the influence of reserve size and boundary length on the relative rate of fish density change in reserves versus fished reference reefs for three exploitable-sized reef fish categories: (1) combined fish (34 species of Haemulidae, Lutjanidae, Serranidae, and hogfish Lachnolaimus maximus); (2) Haemulidae (13 species); and (3) Lutjanidae (9 species). If reef habitat boundaries are highly permeable to fish movements then fish recovery within a reserve would be inversely proportional to: reserve perimeter (RP)/total reserve area (RA) (RP/RA). If, however, reef habitat boundaries are relatively impermeable barriers to fish movements, recovery within the reserve would be inversely proportional to: reserve boundary that intersects reef habitat (HI)/reef habitat area within the reserve (HA) (HI/HA). From 1994 to 2001 we monitored reef fishes within and outside of no-take marine reserves established in 1997 in the Florida Keys, USA. A significant majority of reserves had greater rates of density change than reference reefs for Lutjanidae and combined fish (22 of 24 reserves for both categories). Significantly higher rates of density change were found in ten reserves for Lutjanidae, two reserves for combined fish, and one reserve for Haemulidae. Reserves appeared to promote an increased density of exploitable fishes. A significant, negative, but weakly correlated relationship was found between the relative rate of density change (RDC) for combined fish and the HI/HA ratio. Reserve size and placement appeared to have a minimal effect upon RDC.

     

A way to measure the spread of plants from a focus

The relative frequency of occurrence of plants (or plant parts) is determined at increasing distances from a focus, where the relative frequency is unity. The area under the resulting frequency/distance curve is determined, as a measure of spread. Effect of treatments on spread can be compared by comparing these areas. A rate‐of‐spread index can be calculated from areas determined at successive times.

A model is proposed which enables the area under the curve to be estimated from only three (or even two) frequency determinations. The amount of field work is thereby much reduced.

Use of the model is illustrated by comparing the spread of Pennisetum clandestinum (kikuyu) and several Cynodon cullivars in a nursery.     

Evaluation of a Dairy Herd Improvement Association test to report chronic intramammary infections in dairy cattle

This study evaluated the accuracy of a Dairy Herd Improvement Association test compared with bacterial culture to report the prevalence of chronic intramammary infections in dairy cattle. The Association classification considers a cow to have a chronic intramammary infection when her linear score is 4 or greater for more than one test in a lactation. The threshold level of linear score 6 minimized the sum of the misclassification errors. The Association test was not sensitive or specific enough compared with bacterial culture to classify individual cows accurately.     

Pasture residue amount and sowing method effects on establishment of overseeded cool‐season grasses and on total annual production of herbage

Warm‐season pasture residue may create problems for no‐till overseeding with cool‐season grasses in the USA Southern Plains. Removal of residue to facilitate overseeding, however, represents additional cost and labour that may not be available on small livestock farms. Field experiments were undertaken to assess the effects of above‐surface residues of warm‐season pasture averaging 1·62, 2·48 or 3·36 t DM ha^?1 on establishment and herbage production of Italian ryegrass (Lolium multiflorum) or tall fescue (Festuca arundinacea) overseeded by broadcasting or by no‐till drilling into dormant warm‐season pasture. On average, no‐till drilling was more effective than broadcasting in establishing both grass species, but it was no more effective than broadcasting when used with the greatest amount of residue. Cool‐season grass production was increased by 0·16 when no‐till drilled, but combined yearly total herbage production of cool‐ and warm‐season grasses was increased by 0·07 when cool‐season grasses were established by broadcasting. Amount of residue at sowing did not significantly affect herbage yield of cool‐season grass, but increased residue in autumn resulted in a 0·16 increase in total herbage production in the year following sowing. Residue amount did not affect over‐winter survival of grass seedlings, and productivity benefits of increased residue are small compared with reduced harvest arising from underutilization of warm‐season pasture residue in autumn.     

Effect of stocking biomass on solids,phytoplankton communities,common off‐flavors,and production parameters in a channel catfish biofloc technology production system

The effect of initial channel catfish (Ictalurus punctatus, Rafinesque, 1818) fingerling biomass (1.4, 1.8, or 2.3 kg m^?3) on phytoplankton communities, common off‐flavours and stocker catfish production parameters was evaluated in biofloc technology production tanks. Stocker catfish size (145.5–172.6 g fish^?1) at harvest did not differ among treatments, but net yield increased linearly as initial biomass increased (R² = 0.633). Mean total feed consumption increased linearly with initial catfish biomass (R² = 0.656) and ranged from 10.7 to 15.8 kg m^?3. Total suspended solids (TSS) in all treatments increased linearly with total feed addition, and high TSS appeared to impact negatively daily feed consumption. Initial phytoplankton populations were dominated by small colonial green algae and diatoms, and later transitioned to populations dominated by a small, filamentous cyanobacteria and diatoms. Low, variable concentrations of 2‐methylisoborneol and geosmin were present in biofloc tank water during most of the study and two tanks yielded catfish with 2‐methylisoborneol or geosmin concentrations that might be classified as off‐flavour. One isolate of actinomycete was isolated sporadically from some biofloc tanks, but its abundance was not correlated with 2‐methylisoborneol concentration in tank waters. The microbial sources of 2‐methylisoborneol and geosmin in biofloc tanks remain unidentified.     

Effects of solids removal on water quality and channel catfish production in a biofloc technology production system

Total suspended solids control was evaluated in a channel catfish (Ictalurus punctatus) biofloc technology production system. Settling chamber flow rates were 0.9 (LO) or 2.9 (HI) L/min to reduce total suspended solids to 300 mg/L; solids were not removed from control tanks. Channel catfish yields (7.6–8.7 kg/m³) were not affected significantly, but control fish were skewed toward smaller size classes. Control treatment channel catfish tolerated 1,410 mg/L total suspended solids without adverse effects. LO- and HI-treatment fillet geosmin concentrations were high enough to be designated as off-flavor. Water quality results suggested that nitrification was affected by solids removal.