How Much to Feed your Milkfish ("Bangus") - Use Samples

How Much to Feed your Milkfish (“Bangus”) - Use Samples 

How to tell if bangus being grown in the pond are ready for harvest? How big and heavy are they? What is the range of sizes to date? Pieces per kilo? Number of sacks of feeds still needed? Number of weeks/days to go before harvest? How many kilos are needed per day?

For a bangus grower, these questions always crop up, as they affect operating costs and profits. So it's best to address them based on facts on the ground and not on estimates or guesswork.

Visual check of the fish in the pond is often not effective. A better way is actual sampling of the bangus’ current size, weight, and condition. This is where the use of bangus trap for sampling purposes comes in.

To be sure, there are other ways of getting sample bangus from the pond. But this is how we do it in our bangus farm.

How to Rig up a Bangus Sampling Trap

a. Prepare the following items: large sorting net (“saplar” in Pangasinense) – looks like an inverted mosquito net, 3 bamboo poles or stakes ("tulos" or “onoon”), 2 sets of pulling rope, a scoop net (“tapigo”).

b. Choose the best spot in the grow-out pond wherein to rig up the trap. Usually it’s the feeding area where the bangus have gotten used to being fed commercial feeds and where they tend to flock.

c. Set up two bamboo poles where one end of the sorting net is to be attached. Distance between the two poles should be at least the width of the net.

Trap net (blue) being set up at the feeding area; worker burying one end of pole; black net to the left is the feeding area perimeter net

d. Tie one corner of the net to one stake. Tie the other corner to the second pole. For greater stability, anchor a third pole in between the two stakes; tie the middle part of the net to this third pole.

One corner of net being tied to a pole

Far end of trap net (blue) tied to three poles

e. Extend the sorting net lengthwise toward the side of the pond bounded by the earth dikes. Lay the loose ends of the net on the ground.

f. Attach pulling ropes at each corner of the net. Tie them up temporarily to a stake on the ground or to a tree trunk, or ask a pond helper to hold the rope. 

A pulling rope being attached to one corner of the net near the earth dike

Holding a pulling rope attached to the left corner of the net 

g. When the net is fully extended, depress the net by foot to the pond bottom except the portion attached to the bamboo poles at the far end. Do this until almost all portions of the net are hidden at the bottom.

Net being buried at the pond bottom starting from far end

Pond worker continues to depress net by foot to pond bottom

Trap net almost completely on pond bottom; only the far end of net is visible

h. Cast floater feeds in the area above the hidden submerged net. Out of habit, the bangus will gradually be attracted to the floater feeds.

Floater feeds being thrown in the area above the hidden trap net; see the bangus in feeding frenzy

i. Assign two persons to man the pulling ropes at the side of the pond (one person for each rope) (in this case it's my overseer and assistant caretaker).

Two persons needed to hold a pulling rope at each corner of the trap net

j. When enough bangus flock to and start feeding in the area above the lowered net, pull both ropes simultaneously. Both sides of the net will be pulled up from the bottom as a result. Those caught feeding at the middle will be trapped inside the net.

Two persons pulling the rope attached to the trap net

Trap net after being completely pulled up; see trapped bangus inside

k. Fold the net starting from the bamboo poles at the far end, so that the net’s area is gradually reduced. The trapped bangus will tend to move to one side of the net. Continue folding and tightening the net until all the trapped bangus are retained in a small area.

Net being folded and tightened until all bangus trapped inside are confined in a small space

l. Randomly pick bangus by hand, say 10 to 15 pieces, from the entire catch inside the net and transfer them to a scoop net (“tapigo”). Return the rest of the trapped bangus to the pond. 

Holding a scooping net ("tapigo") where selected bangus samples are placed

m. Sort the randomly picked sample by size (such as market size, size 8, size 10, 12, etc).

13 bangus samples taken from one grow-out pond (Main Pond)

9 bangus samples taken from an adjacent grow-out pond (East Pond) following the same procedure

 n. Weigh the fish by size then divide by the quantity to get the average body weight per fish. Compute the number of pieces per kilo for each size. Get other dimensions: body width, body length including tail, body length except tail.

Below are the results of our actual samples (Note: we conducted sampling using the trap in two grow-out ponds - the Main Pond and East Pond.)

a. Main Pond

Size	Sample Qty	Total Weight (kg.)	Ave. Body Wt/Pc. (gms)	Pcs./ Kilo	Body Width (in.)	Body Length (in.)	Body Length (w/ tail)(in.)
Market size	7	1.5	214	4.7	2.5	9.5	11.75
Size 8	3	.375	125	8	2	8	10
Size 12 (plus)	3	.2	67	15	1.5	6.5	8.25

b. East Pond

Size	Sample Qty	Total Weight (kg.)	Ave. Body Wt/Pc. (gms)	Pcs./ Kilo	Body Width (in.)	Body Length (in.)	Body Length (w/ tail)(in.)
Market size	1	.2	200	5	2.5	8.5	10.5
Size 8	3	.4	133	7.5	2	7.5	9.75
Size 10 (plus)	2	.2	100	10	1.75	6.6	8.375
Size 12 (plus)	2	.15	75	13.3	1.5	6	8
Size 12	1	.05	50	20	1.25	5.5	6.5

Growth of bangus in the Main Pond is more advanced than those in the East Pond (this is as expected because stocking was done a month earlier in the Main Pond). 

As I see it, partial harvest can already be scheduled for the Main Pond in two to three weeks. Based on the table above, more than half of the sample taken were already market sized, i.e., 7 of 13 bangus samples.

As fish farmer, doing partial harvest in, say, two to three weeks will give me the following advantages:

1. provide cash for working capital – such as for buying more commercial feeds for the still undersized bangus

2. reduce the stocking density in the Main Pond and allow faster growth of remaining bangus

3. take advantage of the still favorable pond condition (which is expected to worsen in a few months due to the onset of El Nino in January 2015).

4. take advantage of good timing and expected higher demand and prices for bangus (Christmas season was nearing).

Regarding feeds requirement, see the average body weight per piece of the bangus samples (in grams) in the table above. Determine the amount of feeds to be applied daily (average body weight in grams x feeding rate x stocking density). From this, you can compute the total number of kilos that you will need per day as well as the estimated total number of sacks (each sack contains 25 kilos) until harvest time.

For example, if you have 4,000 pieces of size 12 juveniles, average weight of which is 50 grams apiece. Assume feeding rate of 4% of body weight. This means you need to feed the bangus 2 grams of feeds a day. Multiply by 4,000 pieces, and your total feeds required for the day would be 8,000 grams or 8 kilos.

In our case, we feed 3 times a day. So divide 8 kilos by 3 and you get 2.6 kilos per feeding, 3 times a day. In estimating the number of sacks till harvest time, you need to use a higher average body weight over the next weeks or so, as the bangus grow bigger.

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