•We model intensive production of shrimp considering partial harvesting strategies.•Improving management can increase production from 2690 to 3524kgha−1.•Reduction in variability is obtained by ...improving management and increasing farm size.•Final weight of shrimp, and length of daily aeration are the most important factors.
Partial harvesting is an alternative for managing cash flow of aquaculture farms. We use deterministic and stochastic models to analyze zootechnical, water quality and management factors influencing intensive production of shrimp when incorporating partial harvesting strategies. Data from a commercial farm in the State of Nayarit, Mexico were used for modeling. The main factors affecting shrimp production and its variability were: final weight and growth rate of shrimp, water temperature, pond size, length of daily aeration, and the time when the first partial harvest is conducted. Using the largest pond size (4.0ha), minimum length of aeration (7.5h), and first harvesting at 8.5 weeks resulted in a minimum total harvest of 2690kgha−1 (partial and final harvests of 643, 269, 1075, and 703kgha−1). Using the smallest pond size (1.0ha), maximum length of aeration (7.9h), and first harvesting at 11.5 weeks resulted in a maximum total harvest of 3524kgha−1 (partial and final harvests of 1111, 234, 997, and 1182kgha−1). The increase in shrimp production from improved management was 31%. The stochastic model showed that increasing farm size from 1 to 40ha diminished the variability of shrimp production by 84.0%, meaning a reduction of 2.2% per hectare as size increased. Sensitivity analysis indicated that, overall, final weight of shrimp and length of aeration are the most important factors determining production. The models can be used to determine, in future research, the optimum harvesting strategy, using a bioeconomic approach.
The nutritional response of
Litopenaeus schmitti larvae to substitution of
Chaetoceros muelleri by
Spirulina platensis meal (SPM) was evaluated. The substitution levels (S) were 0%, 25%, 50%, 75% and ...100%, dry weight basis. Final larval length (FL) ranged from 1.98 to 3.16 mm for the different substitution levels. There was a significant relationship between S and FL, described by the following quadratic equation: FL
=
2.853
+
0.01598
S
−
0.000233
S
2. The substitution level (
S) yielding maximum FL was 34.2%. Development index (DI) values ranged from 2.84 to 3.93 and were dependent on substitution level. The corresponding equation was DI
=
3.799
+
0.00945
S
−
0.000189
S
2 (
P
<
0.01). Maximum DI was obtained at 25.0% substitution. Survival was high (82–87%) and no significant differences were found between treatments. Protein digestibility of either microalgae was high, with 92% for SPM and 94% for
C. muelleri, with no significant differences between them. The results in this study indicate that an adequate balance of nutrients in relation to the requirements of the species is critical. To simultaneously improve FL and DI, a 30% substitution of
C. muelleri by SPM is suggested. This is equivalent to feeding 0.15 mg larvae
−
1
day
−
1
dry weight basis of a 70%
C. muelleri/30% SPM diet, representing 0.078 mg protein larvae
−
1
day
−
1
, 0.026 mg lipids larvae
−
1
day
−
1
and 2.732 J larvae
−
1
day
−
1
.
The effect of dietary protein level on spawning and egg quality was evaluated for female Cherax quadricarinatus. Diets containing four different levels of crude protein were evaluated (22, 27, 32, ...and 37%). After 100 days, no significant effects of protein level were found on survival (78.6–84.5%), final weight (41.0–43.1g), or fecundity (8.5–9.2 eggs/g female). The percentage of spawning females ranged from 19.7 to 27.3%, and a significant fit, using a quadratic equation estimated maximum spawning to occur at 30% crude protein. Significantly greater egg area (3.90 mm2), volume (39.3 mm3), weight (5.44 μg), and diameter (2.27 mm) were observed at 32% crude protein. There were no significant differences in mean egg protein (2227.1±445.0 μg/egg), lipid (430.9±85.2 μg/egg) and carbohydrate (73.9±10.6 μg/egg) contents, and energy (13.3±2.1 kcal/egg) in relation to dietary protein level. High statistical power indicated that biochemical composition was not affected by dietary protein level. We conclude that a dietary crude protein content of 32% is recommended for reproduction of female redclaw crayfish.
Our objective was to assess the quality of eggs and juvenile of Nile tilapia (Oreochromis niloticus) from broodstock of three commercial hatcheries (H1, H2, and H3). Larval weight was significantly ...higher for H2 and H3 hatcheries (P < 0.05). After 45-day growth, weight of juveniles of H2 was higher, while specific growth rate was significantly higher for H1 and H2 (P < 0.05). After the ammonia stress test, no significant differences in mortality were found among larvae from the three hatcheries, although a positive relationship between carbohydrate content in eggs and juvenile mortality was observed (P < 0.05). After the salinity stress test, the lowest and highest mortality (P < 0.05) occurred respectively in tilapia larvae from the H1 (24.2%) and H3 (57.8%) hatcheries. We concluded that egg quality was not affected by tilapia broodstock from the three hatcheries studied, but differences were obtained for growth performance, carbohydrate content, and survival of juveniles when exposed to the salinity stress test. These three indexes should be considered as potential juvenile quality criteria for tilapia.
•We used a stock model, multivariate analysis and a stochastic approach to predict shrimp biomass.•Our analysis allowed studying the relationships between production parameters, water quality, and ...management variables.•We conclude that the approach is useful for studying the variability of semi-intensive shrimp production.
We use a stock model, multivariate analysis, and a stochastic approach to predict shrimp production under commercial semi-intensive conditions as a function of water quality and alternative management schemes. Larger final weight of shrimp was obtained when temperature and duration of cultivation increased. Increases in the mortality of shrimp were associated with lower dissolved oxygen levels, shorter durations of cultivation, and higher stocking densities. There was a direct relationship between temperature and stoking density, while dissolved oxygen was inversely related with stocking density and duration of cultivation. Stocking density was inversely correlated with pond size and directly correlated with duration of cultivation. The lowest yields were predicted, using the lowest stocking densities and shortest duration of cultivation; the highest yields were predicted using the highest stocking densities and longest duration of cultivation. Yields increased from 938 to 2326kgha−1 (spring production cycle), and from 982 to 1907kgha−1 (summer production cycle). Improved management resulted in increased shrimp production and diminished variability. Sensitivity analysis indicates that final weight of shrimp and stocking density were the major factors affecting variability of shrimp yields. We conclude that stock models, multivariate analysis, and a stochastic approach constitute an effective method for studying the relationships between production parameters, water quality, and management variables, and, for analyzing variability of semi-intensive shrimp production.
A dynamic stock model was used for quantification of shrimp production and analysis of alternative management schemes of stocking density, pond size, starting time of aeration, and duration of ...cultivation for intensive commercial production of the shrimp
Litopenaeus vannamei. Databases from Mexican farms were used to calibrate the model. Multiple linear regression models were employed to establish relationships between parameters of the stock model and the management variables. Water quality variables (dissolved oxygen, temperature, and salinity) were complementarily analyzed. The final weight of shrimp was directly related to duration of cultivation and dissolved oxygen, and inversely related to stocking density, pond size, and salinity. There were inverse relationships between the growth coefficient and temperature and dissolved oxygen and between mortality rate and temperature. Dissolved oxygen was significantly related to starting time of aeration. Simple linear regression and an equivalence test indicated that biomass at harvest (after 13 weeks in winter, and 20 weeks in summer) was adequately predicted by using the stock model and the multiple regression models. The highest production (winter, 6900
kg
ha
−1; summer, 12,600
kg
ha
−1) were predicted using 60
postlarvae
m
−2, small ponds (2
ha), and starting aeration at the first week of cultivation; while the lowest yields (winter, 2600
kg
ha
−1; summer, 6000
kg
ha
−1) were obtained using 40
postlarvae
m
−2, large ponds (8
ha), and delaying the start of aeration until the fifth week of cultivation. The lowest production was 38% (winter) and 48% (summer) of the highest yield. Using small ponds could be particularly important during winter cycles to increase production, while stocking density and starting time of aeration contributed less. In contrast, pond size played a minor role during summer cycles and stocking density was the most sensitive variable.
► We used a stochastic approach to study the variability of shrimp production. ► Improving management increased mean annual production from 6300
kg
ha
−1 to 16,800
kg
ha
−1. ► White spot disease, ...dissolved oxygen and pond size were major factors determining variability of production. ► The results call for studies on improving aeration management to reduce variability of dissolved oxygen among ponds.
We investigated the variability of shrimp
Litopenaeus vannamei production by incorporating stochastic elements into deterministic stock models and determined the contribution that white spot disease, zootechnical parameters, water quality, and alternative management strategies have on variability. The model was calibrated for intensive shrimp cultivation in the State of Nayarit, Mexico. Mean annual production increased as a consequence of improved management from 8000
kg
ha
−1 to 22,000
kg
ha
−1 when cultivation was not affected by the disease and from 3200
kg
ha
−1 to 10,400
kg
ha
−1 when the disease affected production. When simultaneously considering both cases, mean annual production increased from 6300
kg
ha
−1 to 16,800
kg
ha
−1. White spot disease was a major factor determining variability of production. Shrimp production was particularly sensitive to levels of dissolved oxygen when management was inadequate, while final weight and mortality rate of shrimp were more sensitive when management improved. Water temperature and salinity had intermediate importance, and mortality caused by the disease and the time when mortality occurred had intermediate or low relevance. Improving management increased shrimp production and diminished variability. The duration of cultivation and stocking density were the most important management variables controlling variability of production when cultivation was affected by the white spot disease. When the disease was not present, pond size and duration of cultivation were the main factors affecting production. Starting time of aeration had relatively lower importance in determining variability, while the stochastic values of dissolved oxygen, in contrast, became most important. These results call for studies on improving aeration management to reduce variability of dissolved oxygen in ponds.
Illegal catch of abalone and lobster along the west coast of the Baja California Peninsula (Mexico) was estimated from surveys conducted among fishers and data of custom duties on live lobster ...exported to the USA. We estimated that illegal catch of abalone amounts to 62 t yr–1 (27% of the commercial catch) and illegal catch of lobster amounts to 64 t yr–1 (5% of the commercial catch). The two methods used in this study to estimate the illegal lobster catch yielded similar and consistent results (4.7% of the legal catch when using survey data and 4.5% when using data on custom duties for 1989–2002). We conclude that the methods of estimation are useful and reliable because they are based on direct sources of information. The methods could be used for a bottom-up approach to estimate illegal catch.
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