Bulletin of the Japanese Society of Scientific Fisheries Vol. 36, No. 4, Studies on the Mouth Size of Fish Larvae Akihiko SHIROTA* Studies on

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1 Bulletin of the Japanese Society of Scientific Fisheries Vol. 36, No. 4, Studies on the Mouth Size of Fish Larvae Akihiko SHIROTA* Studies on the mouth size of larval fishes have not yet been fully made. The author measured the mouth size of various larval fishes which had absorbed yolk and just begin to take natural live food, and studied the relationship among mouth size, food size and growth of fish. Total body length of the material fishes ranged from 10 to 20mm. The results obtained are as follows. 1. No definite relationship was found between the mouth size and the total body length at the time of commencement of feeding. 2. The mouth size of various larval fishes at the time of commencement of feeding ranged from 200ƒÊ to 1.000ƒÊ and was observed to have a close relationship to the size of their natural foods: That is, larval fishes having small mouth sizes, such as Hypomesus, Plecoglossus, Ammodytes, Sillago, Konosirus and Oplegnathus take only phytoplankton, pro tozoa and the nauplii of small copepods, but larval fishes having big mouth sizes, such as Thunnus, Katsuwonus, Seriola, Girella, Mugil, Lateolabrax and Clupea were found to easily take large copepods at the time of commencement of feeding. 3. Although the body size at the time of commencement of feeding, in fishes of rapid growth such as Thunnus, Katsuwonus, Seriola and Scomber, was much smaller (about 1/2) than that of Clupea, their mouth size was equal to or larger than that of Clupea. 4. It was made clear that the quicker the growth of fish, the greater is the mouth size at the time of commencement of feeding.

3 i Table 1. The total length and the mouth size of larval fishes in the time of commencement of feeding. Time Body size of larval Egg size Size of from fish in the time of No. Species of fish (mm} hatched larva absorption hatch to commencement feeding of (mm) of yolk Total length Mouth size (days) (mm) (p) 1 Cyprinus carpio 1.2~ Carassius auratus Hypomesus olidus 0.5~ Salmo gairdneri-irideus Plecoglossus altivelis 0.9~ Rhinogobius similis 1.4~ : Mugil cephalus Lateolabrax japonicus ; Oncorhynchus kisutch Ammodytes personatus Konosirus punctatus Etrumeus micropus ( Engraulis japonica Sardinops melanosticta L5~ Spratelloides japonicus i O Clupea pallasi j Harengula zunasi Ilisha elongata Tylosurus melanotus Cololabis saira Hemiramphus sajori 2.1 ~ Trachurus japonicus Scomber japonicus Seriola aureovittata Seriola quinqueradiata Seriola purpurascens Sillago sihama ~ Girella punctata Siganus fuscescens 0, Oplegnathus fasciatus Mylio macrocepoalus Chrysophrys major Katsuwonus pelamis 0.80~ ~ Thunnus albacares Thunnus thynnus Fugu rublipes Platycephalus indices Chelidonichthys kumu ; Gadus macrocephalus Eopsitta grigorjewi ~4.6 I 368

4 Fig. 2. The relationship between the egg size and the total length of fish in the time of commencement of feeding. Figures indicate the species of the fishes given in Table 1. Fig. 3. The relationship between the total length of newly hatched larva and the total length of fish in the time of commencement of feeding. Figures indicate the species of the fi shes given in Table 1.

5 Fig. 4. The relationship between the total length of fish in the time of commencement of feeding and the mouth size. Figures indicate the species of the fishes given in Table 1.

6 Fig. 5. The relationship between the mouth size and the total length of larval fishes in the time of commencement of feeding.

7 Fig. 6. Relationship between the total length of larval fishes and the mouth sizes. Figures indicate the species of the fishes given in Table 1.

8 Table 2. The mouth size of larval fish at different body sizes. Total length of fish * 10 mm 15 mm 20 mm Mouth size Mouth size Species JMouth size' Species Mouth size No. Species of fish ---(mm), of fish (mm) of fish (mm) 1 Thunnus albacares , Katsuwonus pelamis Seriola quinqueradiata Scomber japonicus Seriola purpurascens ~ Lateolabrax japonicus Trachurus japonicas Gadus macrocephalus Chrysophrys major Girella punctata i Mylio macrocephalus , Engraulis japonica Fugu rublipes Harengula zunasi Sardinops melanosticta 426 0, ,5 16 Konosirus punctata Clupea pallasi Cololabis saira X Plecoglossus altivelis * Larval fish in the time of commencement of feeding.

10 Table 3. Species and the size of natural live foods for larval fishes. Fresh-water live foods Species Size Chlorella ellipsoidea 5-3 li x p C. vulgaris 5-10/t Scenedesmus bijuga 4-7 p x 7-18 p S. dimorphus 3-6px16-22p S. armatus 4--8px7-14p S. obliquus I 3-9 p x p S. quadricauda p x u Microcystis incerta 3-4p (colony 100 x 300 p) M. aeruginasa 0.5-4p (colony 5 x 200 p) Euglena oxyuris p x p E. terricola 8-17px68.93p E. rostrifera 18-48px90-140p E. minima 10.15px25-v40p E. retronata 9-15pxl8-34p Daphnia rosea mmx mm D. pulex mmxl.1-2.3mm Ceriodaphnia megops mmx mm C. regaudi 0.25'0.3 mm x mm Bosmina coregonitypica 0.4 mm x 0.45 mm B. longirostris mm x mm Moina dubia 0.11 mm x 0.38 mm M. macrocopa mm x mm M. affinis mmx0.7-1.Omm Glaucoma scintillans 40-50px60p Tetrahymena faurei 40 p x 60 p T. pyriformis 40 p x 55 p Colpidium striatum 4565 px, p Anguillula situsiae 8 p x 0.17 mm x 2.3 mm Limnodrilus gotoii mm x 7-10 cm Chironomus dorsalis 0.13 x 0.7 mm-1.28 mm x 1.3 cm Marine-water live foods Species Size Thalassiosira condensata p x p (max. 5 cells) Skeletonema costatum p x p Chaetoceros compressus px & C. brevis ,x u C. lorenzianus p x C. sp p x p (max. 4-5 cells) C. simplex 3-4px5-10p Trichodesmium thieboutii 5-16 p x 500~600 p T. erytheraeum 5-20 px 100 p Brachionus plicatilis 72 x 96 p-165 x 236 p Eucyclops sp mm x mm Artemia salina 0.19 x 0.46 mm -1.6 mm x mm

12 Fig. 9. The growth of fishes given by various authors.

13 Table 4. The comparison of the mouth size of each larval fish with that of Thunnus albacares in different sizes. Total length of fish 10 mm 15 mm 20 mm Species of fish Percentage (%) Thunnus albacares Katsuwonus pelamis Seriola quinqueradiata Scomber japonicas Seriola purpurascens Lateolabrax japonicas Trachurus japonicus Gadus macrocephalus Chryshphrys major Girella punctata Mylio macrocephalus Engraulis japonica Fugu rublipes Harengula zunasi Sardinops melanosticta Konosirus punctatus I Clupea pallasi Cololabis saira Plecoglossus altivelis

14 Fig. 10. The relationship between the mouth size of larval fish 1 ` 20mm in total length and the growth in one year 1. Thunnus albacares 7. Fugu rublipes. 2. Katsuwonus pelamis 8. Mylio macrocephalus 3. Seriola quinqueradiata 9. Sardinops melanosticta 4. Scomber japonicus 10. Clupea pallasi 5. Trachurus japonicus 11. Cololabis saira 6. Chrysophrys major