Southeast Asian Fisheries Development Center Aquaculture Department
SEAFDEC/AQD Institutional Repository http://repository.seafdec.org.ph
Institutional Reports Quarterly Research Reports
1979
Occurrence of milkfish, Chanos chanos
(Forsskal) eggs around Panay Island, Philippines
Senta, Tetsushi
Aquaculture Department, Southeast Asian Fisheries Development Center
Senta, T., Kumagai, S., & Castillo, N. (1979). Occurrence of milkfish, Chanos chanos (Forsskal) eggs around Panay Island, Philippines. SEAFDEC Aquaculture Department Quarterly Research Report, 3(2), 19–22.
http://hdl.handle.net/10862/2349
Downloaded from http://repository.seafdec.org.ph, SEAFDEC/AQD's Institutional Repository
O c c u r r e n c e o f m i lk f is h , C h a n o s c h a n o s (F o r s s k a l) eggs a r o u n d P a n a y Is la n d , P h ilip p in e s
Tetsushi Senta*, Shigeru Kumagai and Nelson Castillo
On three occasions during his numerous cruises in the Java Sea, Delsman (1926, 1929) found 15 pelagic fish eggs w hich had th e fo llo w in g characteristics: a diam eter o f 1.2 mm, a fin e ly segmented and slightly yellow ish y o lk , no special structures on the chorion, and no oil globules.
Believing these to be o f m ilkfish , he described and illustrated the eggs and the larvae fro m just after hatching up to the fo u rth day. His id e n tific a tio n was proven correct b y the recent success in the a rtific ia l insemination o f m ilkfish eggs b y Vanstone et al., (1977) and Chaudhuri et al., (1977, 1978).
During the four-year period fro m A p ril 1976 to June 1979, the present authors have made a to ta l o f 1,663 larval net tows in th e waters around Panay Island (Fig. 1), 1304 in C uyo East Pass, 171 in Panay G ulf, 114 in the Visayan Sea, 58 in the Sibuyan Sea and 16 around th e Cagayan Islands. Larval net operations were m ost extensive in C uyo East Pass fo r tw o reasons: (1) A n tiq u e is one o f the most productive fry grounds in the Philippines, and (2) th e firs t m ilk fis h eggs ever recorded fro m Philippine waters were fo u n d around Batbatan Island in A p ril 1976. E ffo rts to collect eggs were more extensive in March, A p ril, May and June since the main spawning season o f m ilkfish falls on these months.
A to ta l o f 551 m ilkfish eggs was collected during th e study period: 89 in 1976, 198 in 1977, 82 in 1978 and 182 in 1979. Table 1 compares th e occurrence o f m ilk fis h eggs in th e five areas in March, 1976 — June, 1979 inclusive.
Most of the eggs, 545 o u t o f 551, were obtained fro m C uyo East Pass. In m ost cases, the eggs occurred in small numbers, ten or less in a to w . The m axim um number so far obtained in a single to w was 33 eggs. These figures seem to be very small when th e tw o facts are considered:
(1) m ilkfish has a high fe cu n d ity, 3.1-5.7 m illio n eggs (Schuster, 1960), and (2) A n tiq u e is one o f the best fr y grounds in the co u n try. It is either th a t the areas surveyed did n o t cover the main spawning grounds o f m ilkfish o r th a t m ilk fis h do not spawn in large schools, b u t in pairs, o r at most, in small schools distributed sporadically over a vast sea. In the la tte r case, th e popu la tio n density o f the eggs in a given area at a given tim e w ould n o t be very high and th e d is trib u tio n o f eggs w ould be very patchy.
Table 2 shows the m o n th ly occurrence o f m ilkfish eggs in this area; the greatest mean number o f eggs per to w (0.73) was in A p ril. It is remarkable th a t th is peak o f egg occurrence is about a m onth ahead o f the peak o f fry occurrence in A n tiq u e w hich is in May. V ery o fte n the eggs occurred in shallow waters around islands o r islets such as Batbatan, Seco, Maralison and Maniguin (Fig. 1). Some larval net tow s at stations close to the A n tiq u e coast, such as o f f Pucio P oint, o ff Pandan and o ff H am tic, also yielded some eggs. Furtherm ore, eggs were also fo und at tw o locations q uite rem ote fro m land (12.4 km and 23.4 km away) and rather deep (380 m and 900 m, respectively).
*Visiting JICA Scientist from Nagasaki University, Japan
1 9
The waters around the Cagayan Islands were surveyed only in June 1977, w ith 16 tow s at 14 locations and 5 m ilkfish eggs were found fro m 2 locations. In the Sibuyan Sea, a single m ilkfish egg was recovered near Zapato Island. No m ilkfish eggs were obtained fro m either Panay G u lf or the Visayan Sea, despite rather extensive larval net operations in these areas, particularly in the waters o ff the southwestern coast o f Guimaras and o ff Estancia.
The m ilk fis h eggs were found in waters o f a wide range o f depth, fro m as shallow as 10 m to as deep as 900 m, although m o t o f them were fro m waters dow n to 200 m deep. M a jo rity o f the eggs was fo u n d w ith in a few kilom eters fro m land, except the tw o cases previously mentioned.
The w ater temperatures and salinities at locations o f egg recovery ranged fro m 26.7°C to 30.8° C, and fro m 32.9 p p t to 34.5 ppt, respectively.
The feature th a t Schuster (1960) noted to be characteristic o f m ilkfish spawning grounds locations w ith clear, shallow w ater and sandy or coralline b o ttom , situated at distances not more than 30 km fro m shore — apply well to most o f the locations where the m a jo rity o f the eggs in the present study were found. S till, considerable number o f eggs (24) were found at locations deeper than 200 m. Whether such eggs have been d rifte d fro m shallow spawning grounds, or m ilkfish also spawn in such deep water remains unclear.
Sim ultaneous horizontal tows at the surface and subsurface w ater layers up to 20 m deep showed th a t m ilk fis h eggs are rather evenly distributed fro m th e surface dow n to at least 20 m.
Here may lie some o f the answers to the problem on the mechanism o f larval transport and movement.
A ll preserved m ilkfish were examined fo r th e ir developmental stages. A lthough a considerable number o f larval net tow ings were made at night (2300H to 0200H ), besides extensive daytim e operations, m ilkfish eggs were obtained only between 0400H and 1800H. The eggs found in the early m orning collections were in the early stages o f development; those found later in the day were more advanced. A lm o st all the eggs brought back alive to the laboratory hatched at about 1900-2000H. Based on th e developmental stages o f the recovered eggs and the tim e o f collection, it seems reasonable to conclude th a t spawning in the w ild takes place at m id n ig h t and th a t the incubation period is about 20 hours, a little shorter than th a t in the laboratory.
Lite ra tu re cited
Chaudhuri, H., J. V. Juario, J. H. Primavera, R. Samson and R. Mateo, 1978. Observations on a rtific ia l fe rtiliz a tio n o f eggs and the em bryonic and larval development o f m ilkfish , Chanos chanos (Forsskal). A quaculture 13:95-113.
C haudhuri, H., J. V. Juario, J. H. Primavera, R. Mateo, R. Samson, E. Cruz, E. Jarabejo and J. Canto, Jr., 1977. A rtific ia l fe rtiliz a tio n o f eggs and early development o f m ilk fis h , Chanos chanos (Forsskal). SEAFDEC A quaculture Dept., Tech. Rep. (3 ):21 -28.
Delsman, H. C., 1926. Fish eggs and larvae fro m the Java Sea. 13. Chanos chanos (Forsk).
Treubia 11:281-286.
Schuster, W. H., 1960. Synopsis o f biological data on m ilkfish , Chanos chanos (Forsskal), 1775.
FAO Fish. Biol. Synop. (4): 64 pp.
Vanstone, W. E., L. B. T iro , Jr., A . C. V illa lu z, D. C. Ramsingh, S. Kumagai, P. J. D ulduco, M. L.
Barnes and C. E. Duenas, 1977. Breeding and larval rearing o f the m ilkfish Chanos chanos (Pisces: Chanidae). SEAFDEC Aquaculture Dept., Tech. Rep., (3) :3-17.
F ig . 1 . T h e areas co v e re d b y th e m ilk fis h egg c o lle c tio n su rv e y s in th e P h ilip p in e s , 1 9 7 6 -1 9 7 9 .
2 1
A re a s
C u y o E ast Pass
C a g a y a n c illo w a te rs
P a n a y G u lf
V is a y a n Sea
S ib u y a n Sea
T o ta l
N o . o f eggs 5 4 4 5 0 0 1 5 5 0
N o . o f to w s 1 2 4 0 16 16 8 1 0 5 5 8 1 5 8 7
N o . o f eggs
p e r t o w (% ) 0 .4 4 0 .3 1 0 0 0 .0 2 0 . 3 5
M o n th F M A M J J A S O N T o t a l
N o . o f eggs 0 7 2 3 2 3 1 2 3 2 6 0 0 0 1 0 5 4 5
N o . o f to w s 2 5 1 6 0 4 4 3 4 1 6 1 9 6 4 2 2 1 0 2 3 5 1 3 0 4
N o . o f eggs
p e r t o w ( % ) 0 0 . 4 5 0 .7 3 0 .2 9 0 . 1 3 0 0 0 0 . 0 4 0 0 . 4 2
T a b le . 1 . T h e n u m b e r o f m ilk f is h eggs c o lle c te d in M a rc h -J u n e , 1 9 7 6 - 1 9 7 9 , b y areas.
T a b le 2 . T h e m o n t h ly o c c u rre n c e o f m ilk f is h eggs in C u y o E a s t Pass f r o m 1 9 7 6 t o 1 9 7 9 .
2 2
