THE MOSQUITOFISH Gambusia affinis Adult male (above) and adu lt female (below) Cambusill affinis affinis. Courtesy of Or. L ouis .4. Krumholz . UNITED STATES DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE BUREA U OF COMMERCIAL FISHERIES Fishery Leaflet 525 ( THE MOSQUITOFISH, Gambusia affinis By Lola T. Dees Branch of Reports Divi ion of Resource Development CONTENTS Page Int roduction. • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 1 Range. • • • • • . • . • • . • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • 1 Fo reign introductions. • • • • . • • . • . • • • • • • • • • • • • • • • • • • • • • • • 2 Habitat . • . • . • • • • • • . • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 2 Li fe history. • • • • • • • • . • • • • • • • • • • • • • • • • • • • . • • • • • • • • • • • • 2 Description •••••••••••••••• •••.•••••••••••.••. 1 • • • 2 Food . • . • • • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • 3 Reproduction . • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • 3 TIle young . • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 3 Enemies . • • • • • • . • • • . • • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • 3 Cu lture. • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 3 Dealers . • . • • • • • • • • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • 4 References . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 4 INTRODUCTION Several species of GaInbusia, of t he order Cyprinodontes and the family Poe­ An insignificant-looking little fish, Cant ­ ciliidae, occur in the warm or tropical i",ir1 '1 r(ini" i s largely responsible for mak­ areas of the United States, Mexico, and ing many parts of the world livable for man. Central AInerica. The species used to con­ In 1918 the great value of Gambusia as an trol mosquitoes is Gambusia affinis (Baird and eradicator of the aquatic stages of the Girard). This species has two subspe­ mosquito was first clearly shown when cies: Gambusia a.ffi71is flffinis and Gambusia affinis these fish were used at Camp Hancock in holbrooki. They are known also as mosquito­ Augusta, Georgia. fish, because they feed on mosquito larvae, GaInbusia eat aquatic l arvae of mos­ and as topminnows , since they are shaped quitoes, including the species that cause like a minnow and feed at the surface of the malaria and yellow fever . One female, water. 2 1/ 3 inches long, ate 225 large mosquito larvae within 1 hour, and a male, 1 1/4 RANGE inches long, ate 28 larvae during the same period. At birth Gambus ia commence feed­ The natural r ange of G. a. affinis extends ing on newly hatched mosquito l arvae, which, along the Gulf of Mexico coast from the when i irst hatched, are threadlike animals mouth of the Rio G r ande as far west as a l most microscopic in size. Bay St . Louis, M i ssissippi, and through the If the r e are no aquatic plants or debris Mississippi River a nd its tributary waters (whlch furni sh hiding places for mosquito as far north as central Illinois. Introduc­ larvae) or predators, GaITlbusia will con­ tions have extended the range of G. a. affinis trol a mosquito population . Experiments northward, even into Canada. Theyhave been extending over two summers in Michigan successfully introduced into Arizona, Cali­ r evealed that Gambus i a reduced mosquito fornia , northern Illinois, Indiana, Kansas, p r oductlon 80 to 95 percent in ponds where Massachusetts, Michigan, Missouri, Ne­ natural conditlOns we r e simul ated (Krum­ vada, New Jersey, New Mexico, New York, holz. 1948b) . When introduced into a fish­ Ohio, Pennsylvania, Utah, Washington, Wis: free pond at the helght of the mosquito consin, and probably other States. breedIng season, these mosquitofish brought The other sub s p e c i e s, G. a. holbrooki, about an 80 pe rcent reduction in mosquito ranges from southern New Jersey along the rep roductlon wlthln a week. Atlantic coast to the Florida Keys and along ( 2 the Gulf of Mexico coast as far as Apa­ sewage . In this enviro nm.e nt they stayed at lachicola, Florida. It is not hardy enough the surface at all tim.es a n d appeared to b e to survive northern winters (Wascko, 1950) . respiring at the a irwate r interface. FOREIGN INTRODUCTIONS LIFE HISTORY Both subspecies have been introduced into m.any foreign lands (Hildebrand, 1931; Description Krum.holz, 1948b). In about 1920 the Inter­ national Red Cross asked the United States The two subspecies are alm.ost identical Bureau of Fisheries for brood stocks of in color, fo r m. , and s ize . While the color is Gam.busia for Italy and Spain. The ship­ usually olive o r dull s ilvery, darkest on m.ent of G. a. holbrooki from. Augusta, Georgia, the head and lightest on th e belly, it varies to Italy failed . However, the fish of the according to the cha r a cter of the habitat. sam.e species sent to Spain arrived in Individuals livin g in ditches and drains are fairly good condition and m.ultiplied rapidly. usually pale , a nd those in dark-colored Within a year or so Italy obtained a brood wat er of s w am.p s are dark green, with a stock from. Spain but the fish were unable d i stinct purple b ar b elow the eye . There to withstand the winters in northern Italy. i s f r equently a fine dark line along the In1927, G.a. affinis, hardierthan G. a. holbrooki, s id e s , s om.etim.es a dark blotch below the were shipped from. Carbondale, Illinois , e y e ; a d a r k purplis h blo tch is usually pres­ to Trieste, Italy. These fish survived and e n t on t h e side a bove the vent in the fem.ale. m.ultiplied. The dorsal f in has 2 or 3 transverse rows From. the original intr oductions into of f ine b l a ck spo ts. The anal fin in the Spain and Italy, Gam.busia h a v e been d i s ­ f em.a le i s d ark-edged; the caudal fin has 3 tributed to nearly all south European coun­ o r 4 irre gular transve rse rows of dark tries and to Germ.any and Austria. They s p o ts; the o ther fins are dusky. The fins were introduced also into Palestin e, the a re sm.a ll, and the scales large in propor­ Philippine Islands (from. thence to China tion to the size of the fish. Dark pigm.ent and Japan), Russia, Thailand, Union of outlines each scale . South Africa, Haw aii an Isl ands , th e We st There are a few differences between the Indies , and Argentina. F r om. these pla c e s two subspecies. G. a. holbrooki, has 8 rays in of intr oduction, Gam.busi a sprea d f ar and the d orsal fin, and the third ray of the wide u nti l they have becom.e a lm.ost cos ­ gonopodium. (sexual organ) shows a deep m.opolitan in the warm.er secti on s of the split when exam.ined unde r the m.icro·· world. scope (Innes, 1956) . G . (/. affinis has only 7 rays in the dorsal fin, and the split in the HABITAT third ray of the gonopodium. is lacking. The s exes of the sam.e species differ in The two subspeci es are found in m. any fo rm. and structure . The fem.ale has a types of water whose tem.perature m.ay d eeper body than the m.ale. Fem.ales, whose range from. 400 to 1000 F . They flour ish m. axim.um. size depends on the fertility of in sluggish and standing water, f r esh, th e wat er in which they live, grow through­ brackish or m.arine , clear or m.uddy, deep out life and m.ay reach a length of 2 1/2 or shallow, open or overgrown, but p r efer inches . Males grow little after the gono­ clear shallow water . They probably seek podium. is fo rm.ed (Turner, 1941) and do shallows to escape lar ge p r edacious fish, n ot exc eed 1 1/2 inches. The fem.ale has a such as largem.outh black bas s , and t o feed s m. a ll, r ounded anal fin with the rays con­ on m.osquito larvae , which a r e m.or e nected b y a m.em.b rane, and the m.ale has num.erous there than elsewhere. the th ird , fourth, and fifth anal fin rays Mosquitofish occur in ditches and pool s unit ed a nd lengthened to fo rm. the gono­ containing either hard or bracki sh wat er. podium. (picture on cover). Com.m.on characteristics of these envir on­ G e ne r a lly m.os quitofish, which are rela­ m.ents are a relatively high m.ineral content tively f r ee from. disease, die during the in the form. of dissolved solids and an sum.m.e r in which theym.ature . Som.e fem.ales abundant supply of plant and anim.al food . m.ature in t h eir first sum.m.er of life; others They thrive too in artesian well dischar ges , do not m.atu re until their second sum.m.e r cisterns, water tanks, potholes , and r a in and die w h e n ab out 15 m.onths old . Le s s barrels. They have been known to liv e also har d y tha n f e m.ales, m.ales die at an earlier in an open m.unicipal septic tank containing age. 3 Food ( While adult Gambusia eat princip ally larvae and nymphs of aquatic insects, they also eat plant food such as diatoms, desmid s 1 and fil amentous algae . The young feed mostly on plankton (the passively floating or weakl y swimming animal and plant life). Reproduction Gambusia are OVovlvlparous ; that is, a female p r oduces eggs that hatch within her body. The male fertilizes the eggs in the female b y using the gonopodium to deposit sperm in her genital tract . A female is a b l e to produce several broods of y oung a fter being fertilized once.