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Fish stress induced by handlingand poor feeding practices is acommon cause of cage cultureproblems. Handling stress occurswhenever fish are captured,moved, or confined. Handlingstress is usually associated withseining, holding, hauling, orstocking of fish. Problems associ-ated with incorrect feeding prac-tices are particularly acute incages since no natural foods areusually available to the caged fish,

and water quality deteriorationfrom waste feed has a more directeffect on confined fish. Feedingproblems common in cage cultureinclude poor quality feed, incom-plete feed, inadequate feeding orunderfeeding, overfeeding andfeeding at the wrong time of theday. Many of these problems haveno simple solution and somedegree of stress will occur. In mostcases the management goal mustsimply be to reduce the totalstress placed on the fish by han-dling and feeding practices.

Handling

Caged fish are confined at highdensities in a small area. It should

be obvious, therefore, that thecaged fish are in a situation where

frequent stresses are likely tooccur.

Most cage culturists do not startout producing their own finger-lings. If fingerlings are purchasedfrom outside sources, it is possiblethat they may have already beenstressed in handling.

Common handling stressors dur-ing harvest, holding and transportfrom fingerling ponds to the cul-ture pond include heat or cold

shock, oxygen deficiencies, expo-sure to disease, high ammonia ornitrite levels, pH, shock, over-crowding and rough handling.The first encounter the fish cultur-ist usually has with the fingerlingsis at purchase. Therefore, it is atpurchase that the culturist mustmake a determination of the fin-gerlings health (i.e., quality).Stocking quality fingerlings thatare free of disease and of uniformsize is essential to successful cageproduction.

Purchase fish from a reputableproducer who will guarantee hisproduct. If possible, the finger-lings should be inspected by a cer-tified fish disease specialist. If thatis not possible look for signs ofdisease and stress, such as:

s skin abrasions or discol-orations, thin bodies and varia-tion of skin color within thegroup;

s condition of the fins and gills,frayed fins or pale, swollen anderoded gills;

s odd behavior, weak or erraticswimming, piping and lack ofnet avoidance.

All of these are indicators of prob-lems. Starting with stressed or dis-eased fish will probably lead todisaster and not make cage cul-ture a positive experience.

Stocking into the cage is alwaysstressful on the fish. Appropriateequipment and experience areimportant in transporting fish.Transport the fish in a well oxy-genated container with water thesame temperature as the water thefish were in when purchased. Toreduce stress and remove certainparasites during transport, addsalt to the hauling container (seeSRAC publications 390,Transportation of Warmwater FishEquipment and Guidelines; 392,Transportation of Warmwater FishProcedures and Loading Rates; and393, Transportation of WarmwaterFishLoading Rates and Tips bySpecies). Stock at pond tempera-tures which will not stress the fish(see SRAC Publication No. 163,Species Suitable for Cage Culture). Ifthe temperatures of the pond andthe hauling water differ by morethan a few degrees, temper thefish by slowly adding pond water

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VIPR

January 1997Revised

SRAC Publication No. 164

Cage Culture

Handling and Feeding Caged Fish

Michael P. Masser*

*Auburn University


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to equalize the temperature. Await of at least 20 minutes isneeded for a 10oF change in watertemperature. Failure to properlyadjust the temperature can lead toimmediate death or can lower thefingerlings ability to resist infec-tions and lead to secondary dis-

eases or parasites. Finally, do notfeed the fish for 1 or 2 days afterstocking. Let the fish recover fromthe haul and adjust to the cage.

Problems which occur immediate-ly after stocking were either

brought in with the fingerlings,occurred during stocking, or arean indication of severe pondproblems. A cage culturist shouldknow his pond and its waterquality before stocking, and notstock fish into a pond with prob-

lems. (See SRAC Publication No.161, Cage CultureSite Selectionand Water Quality.)

During the growing season thefish should be disturbed as littleas possible. Moving the cage, lift-ing the cage to look at the fish,netting the fish, swimming orfishing near the cage, or placingthe cage where it is disturbed byother animals can stress the fish.Stress can lead to reduced feedconsumption (i.e., reducedgrowth) and increased incidence

of disease.

Feeding practices

Nutritional stress is common incage culture. In fact, most of thefailures of both research and com-mercial cage culture prior to 1975can be related to feed quality.Today the science of fish nutritionhas progressed to the point that

balanced and complete diets canbe formulated for the importantcommercial species. These com-

plete diets are available fromcommercial feed mills and areessential to the health and growthof caged fish. Caged fish in mostcases will receive no natural foodand, therefore, must have a nutri-tionally complete diet which hasadequate protein and energy lev-els, is balanced in amino acidsand in essential fatty acids, and issupplemented with a complete

array of vitamins and minerals.Many commercial feed mills man-ufacture both supplemental andcomplete diets. The cage producermust be sure he is purchasing acomplete dietone that is suit-able for the species being cul-tured.

Caged fish should be fed a float-ing pelleted feed. Floating feed istrapped inside the feeding ringand will allow the fish farmer theopportunity to observe the fish.Sinking feed will fall through thecage (unless the cage has a bot-tom) and not be eaten by the fish.In general, warmwater speciessuch as catfish, tilapia, bluegilland carp can be successfullyreared from large-sized finger-lings on 32 percent protein com-

plete diets although many fishfarmers prefer 36 percent. Reddrum and striped bass (and itshybrids) need diets with 38 to 42percent protein. Coldwater speciessuch as trout need a higher pro-tein diet of 40 to 42 percent. Pelletsizes normally available include1/8, 3/16, and 1/4-inch diameters.Usually large fingerlings canaccept 1/4-inch pellets. Small fin-gerlings and species with smallmouths (e.g., bluegill) may needto be started on 1/8-inch pellets.

Fish will feed most aggressivelynear their preferred or optimumtemperature and when oxygenlevels are high (i.e., above 60 per-cent of saturation). Oxygen is usu-ally at acceptable levels (unlessheavily overcast) between midmorning and late afternoon. Froma temperature standpoint, warm-water fish such as catfish will feed

better as the temperature rises inlate afternoon in the spring, butprefer mid morning during theheat of the summer. Generally fish

will adapt to any feeding time aslong as it is consistent. Changes inthe feeding schedule should bemade gradually (e.g., not chang-ing more than 30 minutes perday). Most studies have shownthat fish will grow faster and have

better feed conversion if theirdaily feed ration is divided intotwo feedings given at least 6hours apart. This is particularly

true of small catfish, trout, tilapiaand bluegill.

Recent research on cage culture ofcatfish has shown that dusk feed-ing can increase growth andimprove feed efficiency. Dusk isthe natural feeding time for many

species of fish. Dusk feeding can-not be practiced without a meansof nighttime aeration. (See SRACPublication No. 162, CageCultureCage Construction,Placement, and Aeration.) Duskfeeding can begin within 1 hour ofsunset and can continue for anhour or more after sunset. The keyto dusk feeding is not to overfeed(see page 3). If mechanical aera-tion is not available, do not con-sider dusk feeding.

Correctly feeding the proper

amount of feed is extremelyimportant. Overfeeding wastesfeed and money, and can causewater quality deterioration lead-ing to stress and increased inci-dence of disease. Underfeedingreduces the growth rate, total pro-duction and profit. A general ruleof thumb for most warmwaterfish is to feed fish all they will eatin 10 to 30 minutes when thewater temperature is above 70oF.Caged fish, particularly catfish,are sometimes shy and may not

start feeding immediately. Also,when fish are first stocked into acage they usually adjust slowly tofeeding. Keeping good feedingrecords is essential to becoming asuccessful fish producer.

It is a good practice to offer cagedfish one-half of the amount offeed they consumed the previousday, so as not to overfeed if thereis a weather, water quality or dis-ease problem that reduces con-sumption. After adding feed

observe the feeding response,adding more feed as needed at 20-to 30-minute intervals. If the fishhave not consumed the feed after20 to 30 minutes, do not add morefeed. Many producers andresearchers have found that cat-fish will continue to consume feedfor several hours if fed at dusk.The key is to get as much feedinto the fish as they want to eat(satiation) without leaving or


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wasting feed. The more feed eatenthe more fish produced!

Demand feeders have been usedsuccessfully with caged fish. Theproblems with demand feedersare:

1) the fish must be trained to use

the feeders,2) the feeders need frequent

adjustment, and

3) the producer must observefeeding behavior of the fish tohead off water quality and dis-ease problems.

Demand feeders should only beused by experienced producerswho have produced fish usinghand-feeding and feel they knowhow to observe fish behavior.

Demand feeders should be filleddaily at the time when feedingnormally begins, so that feeding

behavior can be observed immedi-ately. Since species like catfishtend to feed on demand feeders atdusk or after dark, it is best to fillthese at dusk. Again, dusk feed-ing (and demand feeding ofspecies that feed at night) shouldnot be practiced unless nighttimeaeration is available!

Fish in cages should be fed atleast 6 days a week, unless pre-

cluded by bad weather, poorwater quality, or disease. Thedaily amount of feed fed will needto be increased as the fish grow.Feeding should be discontinuedduring periods of heavy overcastweather (unless aeration is avail-able) and if water temperaturesexceed 95oF.

Feeding rates

Feeding rates for fish are calculat-ed on a percent of body weight

per day basis, based on the fishsize and water temperature. Smallfish consume a larger percentageof their body weight than largerfish, and all fish increase con-sumption as water temperaturesapproach optimum temperaturerange. Small fingerlings will usu-ally eat 4 to 5 percent of their

consumed each day for the firstweek.

A new estimate should be recalcu-lated each week, based on esti-mated growth. Estimated growthis calculated by multiplying thetotal amount of feed (in pounds)fed during the week by the esti-mated feed conversion ratio (FCR)of 1.0/1.8 (1 pound of gain foreach 1.8 pounds of feed eaten or0.556). This estimated growthweight is added to the totalweight at the beginning of theweek. This new total weight isdivided by the number of fish(less any deaths) to get a newweight of individual fish. UseTable 1 to get the estimated per-cent body weight the fish shouldnow consume and multiply this

by the total cage weight. This isthe new amount of feed thatshould be fed daily for the nextweek. This sounds complicated

but with a little practice itbecomes easy. The formulas andexample which follow shouldhelp.

In this example, the fish wereaveraging 1/2 pound (0.5) each atweek 10 and there had been nodeaths; therefore, 300 fish x 0.5 =150 pounds = total cage weight.At that cage weight they were

consuming 3.75 pounds of feedeach day for 6 days or 22.5pounds of feed during the week.

body weight. After they reachadvanced fingerling size the ratewill decrease to 3 percent andnearing harvest size will drop toonly 2 percent or less (see Table1).

Experienced cage culturists preferto estimate feeding rates. Thereare two methods commonly usedto determine proper feedamounts. One method estimatesgrowth based on feed conversionand adjusts feeding rates weeklyto this estimate. The secondmethod estimates growth basedon a sample of fish from the cageand adjusts feeding rates basedon this sample.

Feed conversion method

This method requires that the ini-

tial weight of the fish stocked beknown and that records be kepton the total weight of feed fedeach week.

For the first week start by deter-mining the average individualstocking weight of the fish (totalweight of fish stocked in poundsdivided by number of fishstocked). Use Table 1 to find thepercent body weight which fishthat size should consume.Multiply the percent body weight

by the total weight of fish stockedinto the cage. This gives theamount of feed that should be

Table 1. Estimated consumption by various sizes of channel catfish*when water temperature is above 70 degrees F.

Average weight/ length per fish % Body weight consumed

(pounds/inches)

0.02 / 4 5.00

0.04 / 5 4.00

0.06 / 6 3.00

0.25 / 9.5 2.75

0.50 / 12 2.50

0.75 / 13.5 2.25

1.00 / 15 2.00

1.50 / 17 1.75

*Applicable to most warmwater species.


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Winter feeding

Many species of warmwater fishcan be overwintered in cages.Tilapia are the exception and willdie as water temperatures reachabout 55oF. Caged fish can be fedduring the winter at a reduced

feeding level. Table 2 gives gener-al guidelines for feeding catfishduring the winter in cages. Float-ing feed can continue to be fedthroughout the winter in theSoutheast. Feeding is usuallymost successful if done on warm,sunny afternoons. Research hasshown that catfish can gain 10 to20 percent of their body weightover the winter if fed, but feedconversion is poor (>3.0).Research has also shown that cat-fish can survive the winter with-

out being fed and may be moreresistant to bacterial diseases ifdeprived of feed.

Finally, probably the most impor-tant aspect of feeding: Do notover-feed the pond. The pondmust decompose and detoxify allorganic matter it receives.Included in this organic matterare plant materials from insideand outside the pond, runoff ofnutrients from fields and pastures(possibly including livestockwastes), all fish wastes and uneat-en feed. Dumping pound afterpound of feed into the pond putsa tremendous burden on thesenatural decomposition systemswhich use oxygen. If the systemsare overloaded the pond will

become depleted of oxygen andthe fish will die. Unless livestockor fertilizer runoff is a problem,the greatest organic load placedon the pond is from the fish feed.

In general, the recommendedmaximum pond feeding rate is

not more than 35 pounds of feedper surface acre of pond per day(35 pounds/acre/day). Even atthis feeding rate problems mayoccur in some ponds. MotherNature is unpredictable andunforgiving! At this feeding ratethe greatest number of pounds offish which should be cultured incages would be 1,750 pounds/acre, calculating that a 1-pound

Consuming 22.5 pounds of feedwith a feed conversion of 1.0/1.8(or 0.556) gives an estimatedweight gain of 12.5 pounds dur-ing week 10. Adding this 12.5pounds of weight gain to the 150pounds of fish (estimated) in thecage at the start of week 10 gives

a new total cage weight of 162.5pounds. Since 300 fish weigh162.5 pounds, or 0.54 poundseach, they will eat 2.5 percent (or2.5/100 percent = 0.025) of their

body weight according to Table 1.Therefore, the new feeding rate(pounds) is 162.5 x 0.025 or 4.1pounds of feed daily. This amountshould be fed each day for sixdays the next week.

Measured growth estimate

This method calculates feedingrates based on the weight of asample of fish from the cage. Thisshould be done at 2-week inter-vals and usually requires that atleast 10 fish be weighed from eachcage. The total weight of the sam-ple of fish is divided by the num-

ber of fish sampled, to get theaverage individual fish weight.This weight is used with Table 1to estimate the percent body

weight consumed. The averagefish weight is multiplied by thenumber of fish in the cage to getthe total cage weight, which isthen multiplied by the percent

body weight consumed to get thenew daily feeding rate. The for-mulas and example which followshould aid understanding.

In this example the fish were aver-aging more than a half pound(0.54) each at week 10 and therehad been no deaths; therefore, 300fish x 0.54 = 162.5 pounds = totalcage weight. At 0.54 pounds eachof the fish should be consuming2.5 percent (or 2.5 divided by 100percent = 0.025) of their bodyweight per day (Table 1). There-fore, the new feeding rate(pounds) is 162.5 x 0.025 or 4.1

pounds of feed daily. This amountshould be fed each day for thenext 2 weeks.

Handling is stressful on the fish,not only those handled but theother fish in the cage trying toavoid capture. During periods ofquestionable water quality orextremely hot weather conditionsit may be best to avoid handlingthe fish and estimate the weightgain.

Sampling Method:

Avg of individual fish = wt of 10 fish/10

New total cage wt = average wt of individual fish x number in cage

New daily feed wt = new total cage wt x % body wt consumed (Tbl 1)

Example for week 10, cage of 300 fish:

Avg wt of individual fish = 5.4/10 - 0.54 (pounds)

New total cage wt = 0.54 x 300 = 162.5

New daily feed wt = 162.5 x 0.025 = 4.1

Feed Conversion Method:

Estimated wt gain = total pounds of feed consumed x 0.556 (FCR)

New total cage wt = estimated wt gain + last weeks total cage wt

Avg wt of individual fish = new total cage wt/total no. of fish in cage

New daily feed wt = new total cage wt x % body wt consumed (Tbl 1)

Example for week 10, cage of 300 fish, feed 6 days per week:

Estimated wt gain (wk 10) = 22.5 x 0.556 = 12.5 poundsNew total cage wt (wk 11) = 12.5 + 150 pounds = 162.5 pounds

Avg wt of individual fish = 162.5/300 = 0.54 pounds

New daily feed wt = 162.5 x 0.025 (2.5/100%) = 4.1 pounds


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fish will eat 2 percent of its bodyweight daily (1,750 x 0.02 = 35).

Recommended pond feeding lev-els can be increased if aeration isavailable. Aeration can helpmaintain dissolved oxygen con-

centrations and support higherdecomposition rates, or at least,keep the fish alive during times oflow oxygen. The recommendedmaximum feeding rate with aera-tion is 60 pounds/acre/day. At

this rate the greatest number ofpounds of fish which should becultured in cages would be 3,000pounds/acre (3,000 x 0.02 = 60).

Feeding rates above these levelsare practiced by many experi-enced cage producers. The key

word is experienced. Beginningcage producers should not pushtheir ponds until they have gainedexperience in water quality andfish management. Unfortunately,much of this experience is usuallygained by killing fish.

Table 2. Winter feeding schedule for caged fish.

Temperature % of Total fishoF weight to feed Feeding frequency

66 - 70 2.0 every other day



51 - 55 1.0 twice per week

45 - 50 0.5 once per week

1. Observation of the fish at feeding time is vital.Feeding behavior is the best index of overallhealth. Actively feeding fish indicate everything isall right, for the moment. Poor feeding behaviorshould always be viewed with suspicion (seeSRAC Publication No. 165, Cage Culture Problems).

2. Reduce feeding levels when water temperaturesdrop below 60o or above 90oF.

3. Reduce or stop feeding on heavily overcast andwindless days. These weather conditions reduceoxygen production and diffusion, particularly ifsequential, and can lead to low dissolved oxygen.Feeding will only complicate the problem. Runaeration if available.

4. Feed quality must be excellent. Purchase feedwhich is known to be complete and keep it storedin a very dry, cool place. Feed should be fed with-in 90 days of the manufacture date.

5. Never feed moldy or discolored feed.

6. Automatic or demand feeders are not recommend-ed for most warmwater species because of theneed to observe the fish feeding (except for experi-enced producers with aeration systems).

7. Keep accurate records on the amount of feed fed.

8. Never feed more than 35 pounds of feed/acre/daywithout aeration or 60 pounds of feed/acre/daywith aeration.

Guidelines on feeds and feeding


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The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No. 94-38500-0045 fromthe United States Department of Agriculture.

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