Arlo W. Fast

Size and feed dependent cannibalism with juvenile snakehead Channa striatus.

Abstract A linear regression model was developed to predict cannibalism in juvenile snakehead Channa striatus . Based on morphological measurements of mouth width, head width and body length, the model relates maximum prey length (TL; mm) to predator TL (TL prey = 26.168 + 0.278 TL predator ). This model was verified with a set of independent data, indicating an underestimate of maximum prey size for a certain predator size. The revised model should be: TL prey = 25.809 + 0.405 TL predator (mm). Size differences substantially increased the rate of cannibalism, but prey: predator TL ratios decreased with increased predator TL. Cannibalism rate was 100% during a 5 day trial when the TL ratio of smaller fish to larger fish was 0.35; but the cannibalism rate decreased to 43% when the TL ratio of smaller fish to larger ones increased to 0.64. Increased availability of formulated feed also reduced cannibalism. With no feed offered, cannibalism was 83%; but decreased to 43% when daily feeding rate was 15% of the larger fishs body weight. Our results indicate that cannibalism is unavoidable with this species, but can be greatly reduced among juvenile fish by size grading and ad libitum feeding.

Growth and survival of larval snakehead (Channa striatus) fed different diets

Abstract Culture performance of larval snakehead ( Channa striatus ) was examined in a three-phase feeding experiment. During Phase I, diet treatments included: no food (NF); formulated feed only (FF); live Artemia nauplii and decapsulated Artemia cysts (LA); decapsulated Artemia cysts only (DC); formulated feed plus live Artemia nauplii (FA); and formulated feed plus Artemia cysts (FC). Fish survivals during Phase I were, respectively, 82% (FA), 78% (LA), 46% (FC), 30% (DC), and 0% (NF, FF). Fish fed DC were longer and heavier than fish in the other treatments. Phase II was a transition period to wean fish onto formulated diets. During Phase III, only formulated feed was provided. Fish previously fed LA had significantly greater ( P Artemia nauplii supplemented with formulated feed for 30 days, then gradually eliminate live food over a 7- to 10-day period; or (2) feed larval snakehead exclusively with live Artemia nauplii for 30 days, followed by 7 to 10 days mixed feeding with both live Artemia and formulated feed, then switch completely to formulated feed.

Some Recent Issues and Innovations in Marine Shrimp Pond Culture

World cultured shrimp production increased from 0.4 million metric tons (MMT) in 1990 to about 0.8 MMT in 1999, or about 25 to 30% of total shrimp supply. Increased production was well below 1.2 MMT predicted 10 years earlier. The primary reason for this shortfall was shrimp disease, which effected shrimp yields worldwide. The most serious diseases were viral, for which there are still few certain solutions. As a result of shrimp disease problems, pond culture practices changed to reduce disease incidence. These changes included: use of specific pathogen free (SPF) and specific pathogen resistant (SPR) shrimp seed; reduced or zero water exchange during pond growout; shrimp culture at inland locations away from coastal influences; use of water recycling and reuse growout systems; development of biosecure systems to prevent disease access during shrimps entire culture cycle; development of probiotics and immunostimulants to reduce disease susceptibility; and genetic selection and improvements through closed, life-cycle culture. In addition, environmental awareness and concerns about shrimp culture sustainability became increasingly important with the informed public during the 1990s. This included concerns about habitat degradation and destruction, reduced biodiversity, and exotic shrimp introductions. Herein we review developments with these culture innovations and environmental issues that have occurred during the last 10 years.

Growout performance of diploid and triploid Chinese catfish Clarias fuscus

Abstract Culture performance of diploid and triploid Chinese catfish Clarias fuscus was evaluated at two temperatures (21.5 and 25.0°C), and with two feed formulations. New Age Pacific (NAP) feed (49% crude protein and 18% crude lipid) and Catfish No. 2 (C2) feed (36% crude protein and 23% crude lipid) were provided once daily at 5% body weight. After 175 days, triploid fish gained more weight than diploids. Both diploids and triploids grew faster at 25°C than at 21.5°C. At the lower temperature, C2 feed enhanced fish growth compared with NAP feed in both ploidies, while triploid fish gained more weight than diploids only with C2 feed. Male C. fuscus grew faster than females regardless of ploidy. Neither fish survival nor condition factor differed among treatments, but the condition factor in diploid males was lower than others. If our results apply to commercial scale, culture of triploids at temperatures >25°C could improve total yield and profitability.

Potential benefits of low energy water circulation in Hawaiian prawn ponds

Abstract Water temperature and pond water dissolved oxygen level are two parameters that are vitally important for optimization in aquaculture production. If the dissolved oxygen level falls below about 2 mg liter−1 and the water temperature drops to less than 22°C, freshwater prawns and other warmwater species of fish and invertebrates become stressed. That stress leads to decreased growth and survival, lower quality product, increased aggression, and reduced income. Artificial circulation of pond water can reduce oxygen stresses and thermal stratification, thereby alleviating conditions of poor water quality. Circulation with low energy pond mixers can increase benthic temperatures in thermally stratified ponds, uniformly distribute phytoplankton, and increase dissolved oxygen levels at the bottom of the pond. These benefits result in less aggression and cannibalism, increased survival, increased growth, and increased production.

Effects of water depth and artificial mixing on dynamics of Philippines brackishwater shrimp ponds

Abstract The effects of pond water depth (0·5, 1·0 and 1·5 m) and artificial circulation (with/without) on certain pond dynamic processes were evaluated in a factorial design. Deep ponds had more uniform temperatures, with less rapid temperature changes, greater whole pond respiration, and greater temperature and oxygen stratification. Artificial circulation reduced thermal and oxygen stratification. Sediment respiration, which was estimated using a new technique, was more than three times greater than plankton and shrimp respiration combined, regardless of treatment combination. Shrimp yields were not significantly different for any of the six treatment combinations.

Paddlewheel aerator oxygen transfer efficiencies at three salinities

Abstract Oxygen transfer rates, or standard aeration efficiencies (SAE) were measured using seven paddlewheel impellers at three salinities (0, 11 and 22‰) and with two aeration devices (0.37 and 0.75 kW) in clean water tests. Oxygen transfer rates increased significantly at higher salinities. With the 0.37-kW aerator, mean SAE values increased 67% at 11‰ compared with freshwater (0‰), while SAE increased 46% at 11‰ with the 0.75-kW aerator. SAE values increased further at 22‰, but the increases were much less. These findings clearly demonstrated a significant salinity affect on oxygen transfer efficiencies with paddlewheel aerators.

A bioenergetics model for an air-breathing fish, Channa striatus

Food consumption, standard metabolism, and growth of juvenile snakehead, Channa striatus, a cannibalistic and air-breathing fish were measured at 24–26 °C under controlled laboratory condition. Snakehead weighing 3.2–29.5 g were evaluated, and were fed smaller snakehead. Based on our observations, we determined bioenergetics relationships between specific food consumption, metabolic rates, and body weight. These values, along with other published parameter values allowed us to construct a bioenergetics model for snakehead. We then verified our model with growth and food consumption measurements from an independent feeding trial. Predicted fish growth closely matched observed growth. Our model underestimated cumulative food consumption when a constant activity value was used, but consumption estimates improved when we used non-constant activity values (1-5 times of standard metabolism). Predicted fish maintenance ration was 1.7% of body weight per day. Food conversion efficiency was greatest (0.59) when fed 2% body weight daily, but declined when daily consumption exceeded 6% body weight. This model provides a useful approach for assessing food requirements of snakehead under controlled condition.

A new method for assessing fish feeding rhythms using demand feeders and automated data acquisition

A new approach to monitoring fish feeding rhythms and associated environmental variables is described. This system includes demand feeders attached to load cells to monitor feed consumption, and environmental probes to monitor variables such as temperature, solar radiation, barometric pressure, dissolved oxygen, turbidity, and pH. Measurements from the load cells and probes are recorded at some desired time interval on a data logger, and the data are then analyzed for correlations between feed consumption and environmental conditions. An example of feed consumption rhythms by Chinese catfish (Clarias fuscus) is given.

Seawater Maturation and Spawning of Rainbow Trout in Hawaii

Abstract Rainbow trout (Oncorhynchus mykiss) were transferred to seawater of 34.3‰ salinity and 11°C and subjected to artificial photoperiods. This resulted in successful, repeated maturations and spawnings. Egg fertilization and survival ranged from 0 to 99%.