Increasing Stocking Density Research Articles

Effects of light intensity, stocking density, feeding frequency and salinity on the growth of sub-adult seahorses Hippocampus erectus Perry, 1810

This investigation examined the effects of light intensity, stocking density, feeding frequency and salinity on the growth of sub-adult seahorses, Hippocampus erectus and the development of the brood pouch in male seahorses. During the 8-week study, seahorses cultured at a light intensity of 1000 lx had higher incremental wet weight and standard length than those at 100 lx and 2500 lx. Seahorse growth rate decreased with increasing stocking density (0.25, 0.5, 1 and 1.5 inds/L, respectively) during the 10-week study. Male seahorses grew much faster than females, with incremental wet weights of male and female seahorses of 6.64 ± 1.601 g and 5.87 ± 1.173 g, respectively, in the 0.25 inds/L treatment. The brood pouches of the males emerged earlier, and the ratio between the pouch length and standard length was higher at the higher stocking densities (1 and 1.5 inds/L). The final body weight, weight gain (WG) and specific growth rate (SGR) of the male and female seahorses that were fed 4 times per day were the highest, while those fed 3 times per day had the highest standard length after 10 weeks of culture. The ratio of the length of male brood pouch to standard length was the highest in the low feeding frequency treatment (fed once a day). The incremental wet weight and standard length of sub-adult seahorses differed significantly among the different salinities (35, 33, 31, 29 and 27‰) after 8 weeks of culture ( F 4,60 = 18.950, F 4,60 = 9.225, P < 0.05) with greatest growth at 31–33‰. Results demonstrated that appropriate light intensity, stocking density, feeding frequency and salinity can improve the growth rate of the sub-adult seahorses and affect the development of the brood pouch in male seahorses.

Stocking density for the intensive rearing of juvenile crayfish, Pacifastacus leniusculus (Astacidae), using Artemia nauplii to supplement a dry diet from the onset of exogenous feeding

Recent advances in intensive rearing of astacid juvenile crayfish have greatly improved the results. This challenges the current application possibilities of the studies performed previously, and new research on density is required. A 100-day experiment was carried out under controlled conditions to evaluate density effects on survival and growth rates of juvenile crayfish in optimal conditions of feeding. Juvenile stage 2 Pacifastacus leniusculus were stocked in fibreglass tanks (1 m2, 200 l water) at 20 ± 1°C and fed a dry diet for salmonids supplemented with restricted amounts of Artemia nauplii. Stocking densities were 100, 300, 600 and 1,000 crayfish m−2. Mean survival rate was reduced significantly with increased stocking density, ranging from 86.33% (100 m−2) to 39.13% (1,000 m−2). All checks showed that at the lowest initial density (100 m−2) animals grew significantly faster those at higher densities, recording a final carapace length of 15.28 mm and weight of 1.08 g. Among the treatments of 300, 600 and 1,000 m−2 no differences were found either in carapace length or in weight throughout the experimental period, with a final mean growth of 14 mm carapace length and 0.72 g weight. The final proportion of animals with chelae autotomy rose significantly with increasing stocking density, ranging from 14.44% (100 m−2) to 41.45% (1,000 m−2). This study shows that diet is a decisive factor for stocking successfully high densities under controlled conditions and provides useful information to set adequate densities in accordance with the production objectives.

The Effect of Understocking Density of Channel Catfish Stockers in Multiple-Batch Production

A multiple-batch study was conducted using stocker catfish (0.09 kg/fish) and carryover fish (0.39 kg/fish) to look at the effects of different stocker densities on fish production. Twelve 0.1-ha ponds were stocked with 7,400; 11,120; or 14,825 stockers/ha, and equal weights of carryover fish (2,268 kg/ha). Fish were fed once daily to apparent satiation with a 32% protein floating feed and aerated with a single 0.37-kW electric paddlewheel aerator. No significant differences were detected for gross, net, and net daily yields, growth (g/d), or survival. Sub-marketable yield (<0.57 kg) increased as stocking density increased. However, marketable yields (≥0.57 kg) were not affected by density. Carryover fish in high-density ponds had a significantly lower (P < 0.05) mean weight at harvest, but mean stocker weight was not different across densities. Economic analysis found breakeven prices increased and net returns decreased with increased stocking density when sub-marketable fish were not considered as revenue. The study indicated the possibility that stockers compete with large carryover fish, particularly at higher densities.

Effect of stocking density on the short-term behavioural responses of dairy cows

The objective of this research was to measure the effects of increased stocking density of stalls and headlocks on the short-term behavioural responses of lactating Holstein cows. Multiparous ( n = 92) and primiparous ( n = 44) cows were assigned to four pens of 34 cows each and stocking densities (100, 113, 131, or 142%) were imposed in a 4 × 4 Latin square design with 7-d periods. Stocking density was adjusted by altering access to free stalls and headlocks. Activity of the cows was recorded continuously with digital video cameras for the last 2 d at each stocking density and time spent as well as mean percentage of cows engaged in lying, standing, and feeding at each 10 min scan sample was determined. Mean percentage of cows feeding over a 24-h period was approximately 20.5% and cows spent approximately 5 h/d feeding, but the percentage of cows feeding during the first 60 min following return from the milking parlour declined ( P < 0.009) with increasing stocking density (67.2, 60.4, 55.0, and 54.8% for 100, 113, 131, and 142% stocking density, respectively). Time spent standing in stalls decreased ( P < 0.01; 2.5, 2.3, 2.2, and 2.1 h) whereas time spent standing idly in an alley increased ( P < 0.001; 1.7, 1.9, 2.6, and 3.1 h) as stocking density increased above 113%. A linear relationship was observed between stocking density and the percentage of cows lying, standing, and idly standing in an alley. The results of this short-term study indicate that stocking densities of stalls and headlocks greater than 100–113% altered the behaviour of lactating dairy cows.

The effect of stocking density on certain broiler welfare parameters

In broiler production, stocking density, i.e. floor surface per chicken, is very important welfare factor which directly and indirectly influences and determines the level of growth of chicken body weight, but it is also related to other welfare indicators. Objective of the paper was to define the broiler welfare in different stocking densities by evaluation of their walking ability (gait score), feathering, incidence and degree of hock burns, foot pad lesions, and by determination of the biochemical blood parameters (glucose concentration, total cholesterol concentration), as indicators of condition of stress. One day old chickens of Hubbard genotype were housed in boxes in floor rearing system, in 3 stocking densities and 5 repetitions of each treatment. Treatment A scored stocking density of 10 birds/m2; treatment B, 13 birds/m2 and treatment C, 16 birds/m2. Results of the trial indicate absence of significance of differences between trial groups of broilers in regard to their walking ability, condition of skin and legs, and stress indicators. In general, broiler welfare in all trial groups was satisfactory. However, determined tendencies of worsening of the condition of litter, increase of the frequency of lower scores for walking ability (gait score), hock burns and foot pad lesions which occur with increase of stocking density, indicate the importance of this rearing factor and need to define limiting stocking densities from the aspect of broiler welfare but also economical efficiency of production. .

Culture of juvenile Murray cod, trout cod and Macquarie perch (Percichthyidae) in fertilised earthen ponds

Juvenile Murray cod ( Maccullochella peelii peelii), trout cod ( Maccullochella macquariensis), and Macquarie perch ( Macquaria australasica) (family Percichthyidae) are reared in fertilised earthen ponds to produce fingerlings for aquaculture and stock enhancement purposes to support recreational fisheries and conservation efforts in south eastern Australia. A total of 102 pond stocking trials were conducted over 13 production seasons to quantify growth, survival, condition and yield of juvenile percichthyids and to explore interactions between these variables and a range of biotic and abiotic factors. Water chemistry and zooplankton within ponds fluctuated widely from 1 week to the next and varied considerably between ponds. Zooplankton was composed of rotifers, cladocerans (mainly Moina and Daphnia), calanoids and cyclopoids. Fish Length-weight, length-age and weight-age relationships are described. Specific growth rates (SGRs) were negatively correlated with both size-at-stocking and stocking biomass for all species. SGRs and fish condition were highest in the weeks immediately following stocking, but declined in latter weeks. Survival rates were variable (0.2‑99%), but generally increased and became less variable over the 13 seasons. Increasing stocking density reduced the growth and condition of fish, but did not affect survival. Significant correlations were detected between various fish production indicators (growth, survival and yield) and several water chemistry and biota parameters (prey abundance), but none were consistent for all three species of fish. Some water chemistry parameters reached levels that may have stressed fish and reduced growth and survival. Declines in growth and condition at higher densities, and in latter weeks following stocking, were attributed to a reduction in the availability of preferred prey due to overgrazing by fish. The influence of percichthyid fish on plankton communities in nursery ponds depends largely on fish biomass and size-selective predation. This study has contributed significantly to the knowledge of nursery pond ecosystems, and led to improved pond management and increased reliability of the production of fingerling percichthyids in Australia.

Effect of temperature, stocking density and fish size on the ammonia excretion in palmetto bass (Morone saxatilis×M. chrysops)

Three temperature levels (18, 23 and 28 °C), three stocking density levels (0.72, 1.42 and 2.84 kg m−3) and two sizes of groups (averaging 104 and 173 g respectively) were used to conduct experiments on the effect of temperature, stocking density and fish size on the ammonia excretion (AE) of palmetto bass (Morone saxatilis×M. chrysops). The AE increased with the increase in temperatures by a significant degree (P<0.05) among different temperature groups. There appeared to be a tendency towards increase of the AE with increased stocking densities, and significant differences (P<0.05) were found among stocking groups. The AE of smaller size-group was significantly higher than that of the larger size-group. Diurnal variation of AE in palmetto bass showed that the AE rose greatly to reach a peak at about 4 h after feeding, and to the lowest values at about 24 h post feeding in all of the experimental groups.

Effects of stocking density of freshwater prawn Macrobrachium rosenbergii and addition of different levels of tilapia Oreochromis niloticus on production in C/N controlled periphyton based system

An on-station trial was conducted to evaluate the effect of stocking density of freshwater prawn and addition of different levels of tilapia on production in carbon/nitrogen (C/N) controlled periphyton based system. The experiment had a 2 × 3 factorial design, in which two levels of prawn stocking density (2 and 3 juveniles m − 2 ) were investigated in 40 m 2 earthen ponds with three levels of tilapia density (0, 0.5 and 1 juveniles m − 2 ). A locally formulated and prepared feed containing 30% crude protein with C/N ratio close to 10 was applied considering the body weight of prawn only. Additionally, tapioca starch was applied to the water column in all ponds to increase C/N ratio from 10 (as in feed) to 20. Increasing stocking density of tilapia decreased the chlorophyll a concentration in water and total nitrogen in sediment, and increased the bottom dissolved oxygen. The concentrations of inorganic nitrogenous species (NH 3–N, NO 2–N and NO 3–N) were low due to maintaining a high C/N ratio (20) in all treatment ponds. Increasing prawn density decreased periphyton biomass (dry matter, ash free dry matter, chlorophyll a) by 3–6% whereas tilapia produced a much stronger effect. Increasing stocking density of freshwater prawn increased the total heterotrophic bacterial (THB) load of water and sediment whereas tilapia addition decreased the THB load of periphyton. Both increasing densities of prawn and tilapia increased the value of FCR. Increasing prawn density increased gross and net prawn production (independent of tilapia density). Adding 0.5 tilapia m − 2 on average reduced prawn production by 12–13%, and tilapia addition at 1 individual m − 2 produced a further 5% reduction (independent of prawn density). The net yield of tilapia was similar between 0.5 and 1 tilapia m − 2 treatments and increased by 8.5% with increasing stocking density of prawn. The combined net yield increased significantly with increasing stocking density of prawn and tilapia addition. The significantly highest benefit cost ratio (BCR) was observed in 0.5 tilapia m − 2 treatment but freshwater prawn density had no effect on it. Therefore, both stocking densities (2 and 3 juveniles m − 2 ) of prawn with the addition of 0.5 tilapia m − 2 resulted in higher fish production, good environmental condition and economic return and hence, polyculture of prawn and tilapia in C/N controlled periphyton based system is a promising options for ecological and sustainable aquaculture.

Cage culture of the Pacific white shrimpLitopenaeus vannamei(Boone, 1931) at different stocking densities in a shallow eutrophic lake

Postlarvae of Litopenaeus vannamei were acclimated and stocked in lake-based cages at the following stocking densities: 10, 20, 30 and 40 shrimp m−2. Another set of shrimp was stocked in concrete tanks as reference samples at 30 shrimp m−2. Significant differences were observed among stocking densities throughout the 95-day culture. The final weight at harvest decreased with increasing stocking density: mean weights of 23.3, 15.8, 13.0, 10.9 and 14.6 g for the 10, 20, 30, 40 shrimp m−2 and reference tanks were observed respectively. There were no significant differences in survival throughout the culture period, ranging between 69% and 77%. Daily growth rates (range: 0.11–0.24 g day−1) and specific growth rates (range: 3.54–4.34%) also differed significantly among stocking densities, both increasing with decreasing stocking density. The feed conversion ratio in the cages did not differ among the stocking densities, ranging from 1.53 to 1.65. The relationship between stocking density and mean individual weight at harvest followed the equation y=81.06x−0.54 (R2=0.938) and that of stocking density and production (in g m−2) is y=58.01x−0.46 (R2=0.834).

Effect of stocking density on the growth performance and yield of Nile tilapia [Oreochromis niloticus(L., 1758)] in a cage culture system in Lake Kuriftu, Ethiopia

This research was conducted to investigate the effect of stocking density on the growth performance and yield of Oreochromis niloticus in cage culture in Lake Kuriftu. The treatments had stocking densities of 50 (50F), 100 (100F), 150 (150F), and 200 (200F) fish per m−3. All treatments were in duplicate. Juveniles with an average weight of 45. 76±0.25 g were stocked in the treatments. The fish were fed a composite mixture of mill sweeping, cotton seed, and Bora food complex at 2% of their body weight twice per day using feeding trays for 150 days in powdered form. The growth performance of O. niloticus was density dependent. The final mean weight of O. niloticus ranged 147.76±0.28–219.71±1.42 g and the mean daily weight gain was 0.69±0.01–1.15±0.02 g day−1. Fish held in cages with lower density were heavier than the ones held at higher densities, and showed higher weight gain and daily weight gain. The most effective stocking density, in terms of growth parameters, was 50 fish m−3. The gross yield (4.5–20.55 kg cage−1) showed a significant difference with increasing stocking density (P<0.05). Moreover, the apparent food conversion ratio (2.48–7.22) was significantly affected by stocking density (P<0.05). However, survival rate was not affected by stocking density (P>0.05). It can be concluded that the most effective stocking densities were at 50 fish m−3 cage for larger size fish demand in a short period and 200 fish m−3 for higher gross production with supplementary feed.

Short Communication: Effect of Stocking Density on Indices of Cow Comfort

The objective of this study was to evaluate the effects of increasing stocking density on indices of cow comfort measured over a 24-h period, during peak lying time (0000 to 0400h), and 1h after the afternoon milking. Holstein cows (n=136) were assigned to 1 of 4 pens, and stocking densities of 100, 113, 131, and 142% were applied in a 4×4 Latin square. Video data were recorded continuously for 2 d after 5 d of acclimation to stocking density and analyzed with 10-min scan samples for the percentage of cows lying in a stall, standing in a stall, standing in the alley, and eating at the manger. Percentage of cows standing idly in the alley increased as stocking density increased above 113% (10.9, 12.0, 14.4, and 16.5% for 100, 113, 131, and 142% stocking density, respectively). Cow comfort index (CCI; cows lying down/cows contacting stalls) and stall standing index (SSI; cows standing in stall/cows contacting stalls) differed little as stocking density increased, but stall use index (SUI; cows lying in stall/cows in pen not eating) decreased beyond 113% stocking density (70.1, 70.2, 68.6, and 66.3 for 100, 113, 131, and 142% stocking density, respectively). During peak lying time, SUI decreased with increasing (80.3, 79.5, 74.8, and 69.6 for 100, 113, 131, and 142% stocking density, respectively) stocking density above 113%, whereas CCI and SSI showed little response. None of the indices varied by stocking density when they were assessed at 1h after milking. These results suggest that more than 1 index of cow comfort may be needed at higher stocking densities to assess both stall usage and cows standing idly in an alley. At higher stocking densities, SUI was reduced, because it reflected not only stall usage but the number of cows standing idly in an alley and not actively feeding and unable to access a stall. The CCI and SSI appear to assess actual stall usage (% cows lying or standing) across the range of stocking densities evaluated in this study.

THIS ARTICLE HAS BEEN RETRACTED: Effects of diet, stocking density and environmental factors on growth, survival and metamorphosis of clam, Paphia malabarica (Chemnitz) larvae

A series of experiments were conducted to evaluate the effects of diet, stocking density and environmental factors on the growth, survival and metamorphosis of short neck clam Paphia malabarica larvae. These experiments examined the following factors: diet [Isochrysis galbana, Nannochloropsis salina and a mixture of I. galbana and N. salina (1:1 w/w)], stocking density (1, 3, 5 and 7 larvae mL−1), light intensity (unshaded, partially shaded and fully shaded) and water filtration (unfiltered and sand filtered). Results indicated that N. salina could replace 50% of I. galbana as a food source for the clam larvae with an increase in growth, survival (47.2%), metamorphosis (33.5%) and early settlement. Larval growth decreased significantly with increasing stocking density. A density of 1–3 larvae mL−1 appeared to be optimal for normal growth of clam larvae. Neither diet nor stocking density used in the study had a significant effect on larval survival. Under partially shaded (light intensity=1000–5000 lx) and fully shaded (light intensity <1000 lx) conditions, larval growth was significantly faster than under direct sunlight (unshaded). Larvae grew significantly faster in the unfiltered water than in the filtered water.

Structural heterogeneity and productivity of a tall fescue pasture grazed rotationally by cattle at four stocking densities

AbstractThe spatial heterogeneity in the structure and the productivity of the vegetation was examined in a tall fescue (Festuca arundinacea Schreb.) pasture rotationally grazed at four stocking densities in the Pampean region of Argentina. The examined pasture was grazed at the stocking densities of 3.6, 4.6, 5.6 and 6.6 animals ha−1 with a two‐paddock 14‐day rotational grazing system. Spatial distribution of plant height was examined as well as the percentages of short patch area (heavily utilized patches) or tall patch area (areas ungrazed or lightly defoliated). In addition, biomass, growth rate and relative growth rate were assessed for both short and tall patches. Grazing generated patchiness in vegetation structure and growth at all stocking densities. Increased stocking density caused an increase in the percentage of the short patch area in the paddocks. Short patches had relatively less live biomass than tall ones, but their relative growth rate was 31% higher than that of tall patches (0.021 ± 0.007 vs 0.016 ± 0.005 g DM g DM−1 day−1). The increase in stocking density enlarged the proportion of short patch areas with higher relative growth rate. The relative growth rate (average between short and tall patches) of the two highest stocking densities was 61.7% higher than that of the low stocking density treatments (0.023 ± 0.006 vs 0.014 ± 0.004 g DM g DM−1 day−1). Although the growth rate of the short patches did not exceed the value of the tall patches, the high value of relative growth rate appeared to indicate a higher photosynthetic capacity of the short patches. Moreover, live biomass did not decrease during the experimental period even in the short patch areas showing that, in the particular conditions of our study, overgrazing did not occur at the range of the stocking density examined.

The effect of mussel seed density on tunicate settlement and growth for the cultured mussel, Mytilus edulis

Anecdotal reports from mussel growers suggest that increased stocking density decreases the settlement and growth of the fouling organisms Styela clava (clubbed tunicate) and Ciona intestinalis (vase tunicate). To evaluate this hypothesis, 15 mussel socks of low (90 mussels per 30 cm), medium (250 mussels per 30 cm) and high (500 mussels per 30 cm) densities were placed on three longlines in the Brudenell estuary in the fall 2005 and in the spring 2006. Sampling was conducted in June, August and October of 2006 to determine the effect of different stocking densities and socking time on mussel productivity and C. intestinalis recruitment and growth. Mussel Condition Index and shell length were not significantly different between the three stocking densities by the end of the field trial in October. In August, the mean length of C. intestinalis was significantly lower on the medium and high density socks and C. intestinalis weight was less on medium and high density socks from the fall socking period (no difference within spring socked densities), however, by the October sampling there was no biologically significant difference in the weight of C. intestinalis between stocking density treatments. Time of socking did not appear to have any significant effect on the results, although the abundance of C. intestinalis was marginally higher in August on the socks deployed in December, 2005. Mussel loss was between 50 and 60% for all treatments, with no clear pattern being evident.

The effect of stocking density of Chinese mitten crab Eriocheir sinensis on rice and crab seed yields in rice–crab culture systems

Normally Chinese mitten crab Eriocheir sinensis were cultured for 2 years, 1 year is cultured from crab larvae to seeds or button sized crab in ponds, tanks or rice fields, the another year is cultured from seeds to market size in ponds, reservoirs or other waters. The present study was conducted to determine the effect of stocking density (0, 3.75, 15, 30 and 60 inds. per m2, respectively) of Chinese mitten crab larvae on rice and crab seed yields in rice–crab culture systems using land-based enclosures (4 m×7 m, with three replicates for each stocking density) at the Panjin Guanghe Fisheries Co. Ltd, in the Liaohe Delta, China. Zoobenthos biomass, production of crab and rice paddy, and economical profit among the treatments were determined. The experiment showed that zoobenthos biomass in rice–crab culture systems was relatively variant and not significantly correlated to these stocking density. The biomass of aquatic plant declined significantly with increasing stocking density. Specific growth rates (SGR) and survival rates of the crab were significantly higher at the lower stocking density (P<0.05); in addition, the ratio of precocious crab and total crab significantly increased with the stocking density increasing (P<0.05); There were not significant effect of presence of crab on yields of rice straw and rice paddy (P>0.05). Net crab yield and net profit were the highest at the 15 treatment (P<0.05), however, the net profits among 3.75, 15 and 30 treatments did not show significant difference (P>0.05) economically. Based on the observations above, a stocking density of 3.75 to 30 inds. per m2 was considered reasonable in rice–crab culture system.

Effects of stocking density on the survival, growth, size variation and condition index of juvenile rabbitfish Siganus rivulatus

Spinefoot rabbitfish, Siganus rivulatus, is an economically important species of herbivorous fish that is relatively easy to rear and thus considered to be suitable for aquaculture. Juveniles are generally reared in nursery systems before being stocked into growout cages or ponds. We report here our evaluation of the effects of stocking density on the survival, growth, feed efficiency and condition index of S. rivulatus juveniles in nursery tanks. The experiment was conducted in a recirculating system of twelve 52-l aquaria connected to a biological filter and a sand filter. Juvenile fish (average weight 6.5 g) were stocked into aquaria at four stocking densities (10, 20, 30, and 40 fish/aquarium) with three replicate aquaria per treatment. Diet was provided at 3% body weight daily divided into two feedings. Fish were weighed weekly for 8 weeks and the diet increased accordingly. Survival was greater than 95% in all treatments, with no significant differences observed among treatments. There were also no differences in specific growth rate (SGR 2.12-2.27) of the fish among treatments. Growth rate was linear during the 8 weeks in all treatments, and harvested biomass increased propor- tionally to stocking density (198, 401, 600 and 785 g per increasing stocking density, respectively). Feed efficiency (FE 0.67-0.71) of the fish did not vary significantly among treatments. The coefficient of variation was high (35-41%) among the harvested fish, but it also did not differ significantly among treatments. The final condition indices of the fish in all treatments were similar to each other but significantly greater than the initial values (P \ 0.05). The results suggest that there is no apparent effect of stocking density at the levels tested on the survival and growth of juvenile rabbitfish.

Grow-out of sandfish Holothuria scabra in ponds shows that co-culture with shrimp Litopenaeus stylirostris is not viable

We examined the potential for producing the large numbers of sandfish (Holothuria scabra) needed for restocking programmes by co-culturing juveniles with the shrimp Litopenaeus stylirostris in earthen ponds. Our experiments in hapas within shrimp ponds were designed to detect any deleterious effects of sandfish on shrimp, and vice versa. These experiments showed that a high stocking density of juvenile sandfish had no significant effects on growth and survival of shrimp. However, survival and growth of sandfish reared with shrimp for 3 weeks were significantly lower than for sandfish reared alone. Increased stocking density of shrimp also had a significant negative effect on survival and/or growth of sandfish. A grow-out trial of juvenile sandfish in 0.2-ha earthen ponds stocked with 20 shrimp post-larvae m−2, and densities of sandfish between 0.8 and 1.6 individuals m−2, confirmed that co-culture is not viable. All sandfish reared in co-culture were dead or moribund after a month. However, sandfish stocked alone into 0.2-ha earthen ponds survived well and grew to mean weights of ∼400 g within 12 months without addition of food. The grow-out trial demonstrated that there is potential for profitable pond farming of sandfish in monoculture. Further research is now needed to identify the optimal size of juveniles, stocking densities and pond management regimes.

Effects of stocking density on growth, yield and profitability of farming Nile tilapia, Oreochromis niloticus L., fed Azolla diet, in earthen ponds

Two consecutive experiments were conducted to study the effects of stocking density on growth, food utilization, production and farming profitability of Nile tilapia (Oreochromis niloticus) fingerlings (initial mean weight: 16.2 ± 0.2 g) fed Azolla, as a main component in diet. In experiment 1, fish were hand-fed twice daily with three isonitrogenous (28.5% crude protein) and isocaloric (14.5 kJ g−1) diets A30, A35 and A40 containing 30%, 35% and 40%Azolla, respectively, for 90 days. Diets were formulated by mixing Azolla with locally available by-products. No significant differences were found in growth parameters and production (P>0.05). Total investment cost was significantly higher with A30 (P 0.05). In experiment 2, three stocking densities, 1, 3 and 5 m−2, were assigned to three treatments T1, T2 and T3 respectively. Fish were hand-fed twice daily with diet A40. The final mean weight (89.53–115.12 g), the mean weight gain (0.81–1.10 g day−1), the specific growth rate (1.90–2.20% day−1) and the apparent food conversion ratio (1.29–1.58) were affected by stocking density, with significant difference (P 0.05). Yield and annual production increased with increasing stocking density, ranging from 7.10 ± 0.90 to 25.01 ± 1.84 kg are−1 and 28.79 ± 3.66 to 101.42 ± 7.48 kg are−1 year−1, respectively, with significant differences between all densities (P<0.05). Higher stocking density resulted in higher gross return and lower cost of fish production, with significant variations (P<0.05). The net return increased with increasing stocking density (P<0.05). However, both densities of 3 and 5 m−2 produced the same profitability values. On the basis of growth values and economic return, it was concluded that Nile tilapia could be raised at a density of 3 fish m−2 with A40 to improve production and generate profit for nutritional security and poverty alleviation in rural areas.

The Effects of Breeding Systems and Stocking Density on Some Blood Parameters of Rock Partridges (Alectoris graeca)

In this study, the effects of breeding systems and stocking density on some blood parameters of rock partridges [total protein, total cholesterol, triglyceride, urea, glucose, calcium, phosphorus, alkaline phosphatase (ALP), sodium, chlorine, potassium, aspartate amino transferase (AST), and alanine amino transferase (ALT)] were investigated. For this purpose, blood samples of 18-wk-old male rock partridges, which were bred on the ground and in cages with 3 different stocking densities (group I: 15 partridges/m(2); group II: 20 partridges/m(2); and group III: 25 partridges/m(2)) were examined. Breeding method of rock partridges was found to have significant effects on blood total protein, (P < 0.05), total cholesterol (P < 0.05), triglyceride (P < 0.01), urea (P < 0.01), glucose (P < 0.05), calcium (P < 0.05), phosphorus (P < 0.01), ALP (P < 0.05), sodium (P < 0.01), chlorine (P < 0.05), and potassium (P < 0.01) levels, whereas it was found to have no significant effect on blood AST and ALT levels (P > 0.05). Stocking density of rock partridges was also found to affect significantly the levels of blood total protein, total cholesterol, triglyceride, urea, glucose, calcium, phosphorus, ALP, sodium, chlorine, and potassium (P < 0.05), whereas it did not have a significant effect on blood AST and ALT levels (P > 0.05). When the breeding method of the partridges was changed from the ground to the cages and the stocking density was increased, it was observed that the levels of blood total cholesterol, triglyceride, urea, glucose, sodium, and chlorine increased, whereas total protein, calcium, phosphorus, ALP, and potassium levels decreased. It was understood that the reactions of partridges toward breeding systems and stocking density were different and passing from ground system to cage system, and the increase in stocking density caused significant changes in blood parameters.

Assessing the effect of interventions on the risk of cattle and sheep carrying Escherichia coli O157:H7 to the abattoir using a stochastic model

Escherichia coli O157:H7 persists in being a threat to food safety. The mechanisms behind the spread of E. coli O157:H7 on the farm are complex and poorly understood. The objective of this study was to apply a Monte Carlo model, constructed to simulate the propagation of E. coli O157:H7 in cattle and sheep on the farm, to both test the effect of different interventions on the risk of animals carrying E. coli O157:H7 to the abattoir and to develop understanding of the underlying processes, including the identification of areas that could benefit from further research. An overview of the model including key assumptions is given. The output statistics from batches of 100 runs of the model were collected. From the model output, a cumulative frequency distribution of the prevalence and specific shedding level for the groups of cattle or sheep being sent to the abattoir were generated. Stochastic dominance was used to compare the results of the model outputs. Using the shorthand that “risk” means the likelihood of carrying E. coli O157:H7 to the abattoir, key conclusions from the study included: mixing sheep and cattle increases the risk in both groups; merging groups of animals of the same species into larger groups increases the risk substantially; increasing stocking density increases the risk independently of group size; decreasing the group size decreases the E. coli O157:H7 prevalence independently of stocking density; a very high level of barn hygiene reduces the risk; a shorter time between spreading farmyard manure and grazing and an increased background level of E. coli O157:H7 in the model increases the risk. The background level could be influenced by the presence of wild animals carrying the organism. The parameters to which the model is most sensitive are those related to transmission from grass and enclosures to animals, pathogen survival on grass, in slurry and in barns and contact between animals.