Raul H. Piedrahita

Reducing the potential environmental impact of tank aquaculture effluents through intensification and recirculation

Abstract Aquaculture effluents may contain a variety of constituents that could cause negative impacts when released into the environment. The constituents include dissolved or particulate organics, nutrients, and specific organic or inorganic compounds. Their impact on the environment depends on the total amount or concentration released and the assimilative capacity of the environment for the particular constituent. In this paper, the different types of constituents will be reviewed as they relate to a current trend in the aquaculture industry: intensification of production and recirculation systems. Although most water treatment methods used in intensive or recirculating aquaculture systems result in a relocation of nutrients and organic matter and not in an overall reduction in discharges, this relocation makes it possible to reduce potential environmental impacts by facilitating effluent treatment. For example, solids removal operations produce a stream with high concentration of solids (the sludge removed from the flow) that is also rich in nutrients and organic matter, while reducing the concentrations of these parameters in the culture water. The stream with a high concentration of solids could be treated prior to disposal using techniques appropriate for high strength wastes and sludge. The fate of constituents will be examined for a variety of water treatment operations. The impacts of a number of treatment methods on these constituents will be discussed from the standpoint of overall mass discharges and concentration of the constituents in the discharge flow.

Ontogenetic development of the digestive system in California halibut (Paralichthys californicus) with notes on feeding practices

Abstract The development of the digestive tract and accessory glands in California halibut (Paralichthys californicus) is described from hatching to metamorphosis (42 days post-hatch, dph) at 18 °C. Differentiation of the alimentary canal into the buccopharynx, esophagus, pre- and postvalvular intestine, and rectum was complete by 3 dph (2.7±0.1 mm standard length, SL) coinciding with the time of first feeding. Zymogen granules (pancreatic enzyme precursors) were detected in the exocrine pancreas 1 day before the onset of exogenous feeding and their number increased after first feeding, confirming the importance of pancreatic secretions during the agastric period of larval development and their genetically rather than dietarily induced secretion. The stomach was morphologically differentiated at 27–30 dph (7.2–7.5 mm SL) coinciding with the onset of eye migration. At this stage, gastric glands were abundant in the fundic region and cardiac and pyloric regions were also clearly distinguishable. Supranuclear bodies were observed in the postvalvular intestine throughout the study period, although the number decreased as the stomach differentiated and extracellular digestion took place. The reduction of supranuclear bodies might be due to a change in the protein digestion mechanism. Histological observations showed that Artemia-fed larvae had almost intact nauplii in the postvalvular intestinal lumen and rectum, suggesting a fast intestinal transit in California halibut larvae, and a limited availability of nutrients from brine shrimp nauplii. Special attention might be required in rearing tanks during the first week of exogenous feeding, since the desquamation of the esophageal epithelium and the absence of mucous secretion due to the lack of functional goblet cells may promote bacterial infections under poor water quality conditions.

Oxygenation and carbon dioxide control in water reuse systems.

Control of dissolved gases, especially oxygen and carbon dioxide, is an essential component of intensive water reuse systems. Control of both dissolved oxygen and carbon dioxide concentrations is typically carried out by means of gas transfer processes, although chemical processes are also used to control carbon dioxide concentration. Theoretical and practical considerations of oxygenation and carbon dioxide removal are reviewed in this paper. The theory of gas transfer is presented in general terms, followed by a more detailed description of the basis for a new calculation procedure for carbon dioxide degassing processes. Equipment used for oxygen injection is described, and a new method for estimating packed column degassing parameters is introduced.

Modelling temperature variation and thermal stratification in shallow aquaculture ponds

Abstract A mathematical model to stimulate thermal stratification in shallow aquaculture ponds is described. The dynamic, mechanistic model was developed to simulate the water column of ponds in discrete, completely mixed, horizontal volume elements. Energy exchanges between the ponds surface and atmosphere were calculated with theoretical and empirical relationships commonly applied to heat balance calculations in lakes, reservoirs and waste treatment ponds. Energy transfer between the volume elements caused by turbulent mixing were simulated as functions of the temperature gradient in the water column and a diffusion coefficient. The value of the diffusion coefficient was calculated in each time step as a function of wind speed, depth, and the water column density gradient. The model was implemented using a dynamics simulation language (STELLA™) using an Apple Macintosh™ microcomputer. Also described are the model calibration and verification procedure and results.

Settling velocity characterization of aquacultural solids

A top-loading settling column is described and used to characterize the settling properties of the solids in the discharge water from a commercial rainbow trout production facility. Mass-based and phosphorus-based settling curves are presented. The median settling velocity on a mass-basis for the settleable solids was 1.7 cm s 1 . The median settling velocity for the settleable phosphorus was 1.15 cm s 1 . Manually stripping fecal material from rainbow trout resulted in settleable solids with a median settling velocity of 0.7 cm s 1 . Examination of the settling velocity curves show that halving the overflow rate (OFR) from 2 to 1 cm s 1 changes the removal efficiency from 0.61 to 0.73, an increase of about 20%. Halving the OFR again to 0.5 cm s 1 increases the removal efficiency to 0.81, an improvement of about 11%. Settling characteristics of aquacultural solids will vary from facility to facility. The methods described in this paper can be used to perform a similar type of analysis at other aquacultural sites, which may be growing other species under different management regimes.

The Relation Between Phytoplankton and Dissolved Oxygen in Fish Ponds

Abstract The relationship between phytoplankton density in fish ponds and the level of dissolved oxygen at dawn is described herein by two mathematical models: an analytical model which predicts the upper limit to oxygen production by phytoplankton, and an empirical model based on data from channel catfish ponds. With both models, intermediate densities of phytoplankton are predicted to produce higher dissolved oxygen concentrations. Sensitivity analysis of the analytical model indicates that the main factors affecting dissolved oxygen concentration at dawn are levels of nonalgal turbidity, total plankton respiration, inorganic nutrient depletion, and algal biomass. Good agreement is obtained between dissolved oxygen concentrations predicted with the two models when parameters in the general model are adjusted to values appropriate for catfish ponds. This analysis suggests that aquaculturists can raise dissolved oxygen levels by increasing algal growth, not necessarily by reducing algal biomass.

Aquaculture pond ecosystem model: temperature and dissolved oxygen prediction — mechanism and application

Accurate characterization of temperature and dissolved oxygen stratification in ponds used for aquaculture is of critical importance in understanding how these ponds may be constructed, oriented, or otherwise managed biophysically when one wishes to provide optimal environmental conditions for the organisms being cultured. While field studies can provide characterizations of water quality stratification at a single locale, to date there have been few attempts at developing reliable models which can be used at a variety of sites after initialization with appropriate local geographic and atmospheric data. In conjunction with the Pond Dynamics/Aquaculture Collaborative Research Support Program (PD/A CRSP), the authors have developed a water quality model (the Aquaculture Pond Ecosystem Model, A.P.E.M.) which predicts temperature and dissolved oxygen stratification at several sites, including Thailand, Rwanda, and Honduras. Advances in model structure and reduction of data requirements relative to previous models reflect the desire to provide for culturists the ability to predict stratification events with commonly available data, obtained either by hand or from a simple weather station located at or near the pond site. Strategies used for dealing with the reduced data sets, and the associated assumptions made, are also presented. Lastly, a series of simulation runs is performed to assess the quantitative effects on temperature and dissolved oxygen concentration generated by varying pond depth and phytoplankton density input values.

Development of California Halibut, Paralichthys californicus, Culture

Abstract In contrast to freshwater aquaculture and the culture of anadromous species such as salmon, marine fish culture is in its infancy. The small larval size of many marine species presents significant challenges to culture, however, these highly valuable fish offer considerable promise for aquaculture. A particularly attractive group for marine aquaculture is the flatfish. The California halibut, Paralichthys californicus, with a range in nature from Washington State south to Baja California Sur, Mexico is one such species. With the goal of enhancing the fishery for this species, a hatchery program was developed over a decade ago. The hatchery at Redondo Beach, California, maintains a group of adults that routinely spawn throughout most of each year. Further development of routine culture and juvenile growout techniques ultimately aimed at commercial aquaculture was initiated last year with support from the California Sea Grant College Program. Profitable commercial ventures culturing various flatfish species already exist in other parts of the world, but development of a flatfish culture industry in California confronts unique challenges. Two challenges in particular are the relatively high cost of energy and stringent environmental regulations. To meet these challenges, a culture system built around recirculation technology is being developed that would allow for an energy-efficient industrial-like approach to the culture of California halibut while minimizing environmental impacts.

Apparent ammonia-nitrogen production rates of white sturgeon (acipenser transmontanus) in commercial aquaculture systems☆

Abstract Ammonia production rates of white sturgeon (Acipenser transmontanus) were measured at three commercial farms in the Sacramento, California area. Mean daily ammonia-nitrogen production (RNH3) values ranged from 1.5 to 27.6 mg total ammonia-nitrogen (TAN) (kg fish)−1 h−1 for sturgeon ranging in size from 0.09 to 3.8 kg. Peak hourly average ammonia production rates were observed to occur 2–6 h after the consumption of a meal, reaching values as high as 1.4 times the mean daily values. Multiple regression analysis determined that 87% of the variations in the RNH3 values could be attributed to variations in protein ration, and the protein ration was the only variable considered which was significant in predicting the mean daily ammonia production rates.

Geosmin and 2-Methylisoborneol Cause Off-Flavors in Cultured Largemouth Bass and White Sturgeon Reared in Recirculating-Water Systems

Abstract Earthy and musty off-flavors were present in the fillets of largemouth bass Micropterus salmoides and white sturgeon Acipenser transmontanus grown in partial water-recirculating aquaculture systems. Solid phase microextraction–gas chromatography–mass spectrometry revealed that geosmin and 2-methylisoborneol in the flesh of these fish caused these off-flavors.