SOME ASPECTS OF THE BIOLOGY OF THE RHOMBOID MOJARRA DTAPTERUS RHOMBEUS IN PUERTO RIC01

HERBERT MARTIN AUSTIW Department of Marine Sciences, University of Puerto Rico, Mayagilez, Puerto Rico

ABSTRACT The rhomboid mojarra, Diapterus rhombeus Cuvier, is a fish commonly found over soft bottoms in southwestern Puerto Rico. The spawning season is protracted, lasting from January through September, and the age at maturation is 11 to 13 months. Growth is linear in juvenile fish up to 70 mm (7 months). Their average rate of growth is 10 mm/ month. Fish 70-100 mm long (12 months) grow at an average rate of 9 mm/month. After one year, growth drops off to 5 mm/month. The diet consists of plants, pelecypods, crustaceans, and polychaetes; mud also comprises a very large percentage of the stomach content. Growth and changes in the seasons are reflected by changes in the diet.

INTRODUCTION The mojarras, family Gerreidae, are silvery, inshore fishes. They are characterized by having a highly protrusible mouth which they can extend, tubelike, into the substrate during feeding, and a sheath of scales along the bases of their median fins. The Gerreidae are New World fishes, with the exception of two species found in Africa and Australia. For the most part they are tropical-subtropical euryhaline fishes with some species even adapted to a total freshwater environment. Work published during the last 70 years on the mojarras in the Caribbean and adjacent regions has been limited principally to distributional studies related to regional fish surveys (Evermann & Marsh, 1900; Breder, 1934, 1945; Nichols, 1929; Hildebrand, 1939; Schultz, 1949; Gunter, ]957; Manning & Tabb, ]961; Gunter & Hall, ]963; and Erdman, 1967). Al- though the rhomboid mojarra, Diapterus rhombeus Cuvier (Fig. ]), is one of the more common fishes found over soft bottoms in Puerto Rico and Venezuela there have as yet been no comprehensive biological studies of this species. This paper is a contribution to the knowledge of one of the most common inhabitants of the Caribbean soft-bottom community.

COLLECTIONS Monthly collections were made from Mayagliez Bay, Puerto Rico, using a 16-foot shrimp trawl (cod end ] -inch mesh). Samples were collected

1 Contribution No. 27\ from the Department of Oceanography, Florida State University. This paper is based on a thesis submiLted in partial fulfillment of the requirements for the Master of Science degree at the University of Puerto Rico. The work was funded by PRWRRI, No. 14-01-0001-710. 2 Present address: New York Ocean Science Laboratory, Box 867, Montauk, New York 11954. 1971] Austin: Biology of the Rhomboid Mojarra 887

FIGURE 1. Diapterus rhombeus Cuvier, 100 mm SL, Mayagiiez Bay, Puerto Rico. from Playa Papayo, La Parguera, and EI Faro, Guayanilla, P.R. (Fig. 2), by means of a 50-foot seine (mesh 14-inch, stretched). All samples were preserved in 10 per cent formalin. All measurements of length in this paper are standard lengths.

METHODS Reproductive Biology.-The spawning season was defined on the basis of gonadal displacement volumes, diameters of ova, and the deposition of spawning checks on the scales. Regression analyses of standard length versus spawning condition were used to determine the age at maturation. It was possible to determine the location of spawning and nursery grounds on the basis of field collections of ripe, spent, and juvenile individuals. Food Habits.-The total displacement volume of the stomach and upper intestinal contents was recorded. The volumes of the individual contents were recorded after sorting. Volumes of molluscan and crustacean shells were included whether or not the body was still present. The residual volume (mud, sand, and plant fragments) was also recorded. This 888 Bulletin of Marine Science [21(4)

COlLECTION SITES

PUERTO RICO

\$ FiGURE 2. Collection sites. residue was then counted on a bacterial counting grid. The percentage of the total grid count which each item constituted was expressed as a percentage of the residual volume and, in turn, of the total volume. Volumetric percentages and percentage of occurrence were also recorded. Ecological Observations.-During the course of the study, ecological rela- tionships were noted, including the occurrence of juveniles of D. rhombeus as prey, and infra-generic zonation.

RESULTS AND DISCUSSION Spawning Season.-The collection of many nearly ripe females one month, and of spent ones the next, is an indication that fish have spawned between 1971J Austin: Biology of the Rhomboid Mojarra 889 3·0 ml

ripe IV

ripening III

spent •..c: V ~ 1·00 ~ resting,II § 0'5 i~lTQture 0'10..- f FIGURE 3. Range, mean, 95 and 99 per cent confidence intervals for dis- placement volumes of ovaries at each reproductive stage of Diapterus rhombeus. the times the collections were made (Beardsley, 1967), and on this basis the approximate date of spawning may be estimated. The appearance of fry is further evidence of recent spawning; and based upon their growth rates one may extrapolate back in time to affix a spawning date on a class of juvenile fish (Erdman, 1958). Menon (fide de Sylva, 1963) suggested that tropical fish may form a spawning check on the scale in lieu of annuli. Gonads and ova were divided into five classes or stages based upon their physical condition (Figs 3, 4). Stage I, immature: Gonads very small, displacement volume less than 0.1 ml; sex indistinguishable; diameter of ova 351l-431l' Stage II, resting: Determination of sex usually possible; ovaries pink, oblong and flat, displacement volume between 0.1 and 0.7 ml; eggs usually not visible to the unaided eye (l001l-350Il); testes white, long, and fiat. Stage III, ripening: Ovaries round, pink (tan in alcohol); and with many small eggs (2821l-3181l) visible to the unaided eye; displacement volume more than 0.3 ml but less than 1.0 ml; testes pink, not flat, now more triangular in cross section. Stage IV, ripe: Ovaries distended, walls thin and easily broken; yellowish (tan in alcohol), filled with large eggs (35] 1l-4181l); displacement volume more than 0.7 ml but less than 1.3 ml; testes milk-white, extruding milt. Stage V, spent: Ovaries translucent, anterior end often in ripe condition, with posterior end appearing as in ripening condition; posterior end with large loose eggs (4461l-5041l); often with large blood vessels; displacement volume variable from 0.3 ml to more than 1.2 ml. The distribution of gonadal stages III through V, by month, from March 1966 to September 1967, is presented in Table 1. Fish were 890 Bulletin of Marine Science [21(4) v

IV 500

400 III

t1l II > 0 '0300 ripe '- <;l'" E ,!]! fripening Cl 200

100 I T. resting

~mmature

FIGURE 4. Range, mean, 95 and 99 per cent confidence intervals for diameters of ova at each reproductive stage of Diapterus rhombeus. found in stages III through V nearly every month of the year, which in- dicates a somewhat protracted spawning period. A composite spawning season (Fig. 5, Table 2) based on 2 years' data is shown for July and early August; ripening fish were encountered between January and April, and spent fish during September through December. These calculated breeding seasons were further substantiated by the formation of spawning checks. During the growth portion of the year, material is deposited along the margins of the scales. Each month there- after, the spawning checks are farther from the margin. Measurements of the distance of the spawning check from the margin of the scale enable a rate of deposition to be established. Based upon these rates, back- extrapolation of the checks placed their formation during March or April and September or October, 1966, substantiating that the fish did spawn during the early spring and fall of 1966. Spawning Grounds.-Both ripe and spent females and males were col- lected from the outer, deep margins of the muddy bays inhabited by D. rhombeus. Although no plankton collections for eggs were made to 1971] Austin: Biology of the Rhomboid Mojarra 891

TABLE 1 DISTRIBUTIONOF GONADALSTAGESIII THROUGHV BY MONTH FOR MATURE (125 MM SL) FEMALESOF Diapterus rhombeus IN MAYAGUEZBAY,MAYAOUEZ, PUERTO RICO, MARCH 1966-SEPTEMBER 1967

No. females Total Total over III IV V III-V no. no. 125 mm fish females SL No. % No. % No. % No. % 1966 March 36 29 16 4 25 4 25 1 6 9 56 April 31 8 4 1 25 0 0 2 50 3 75 June 23 18 4 0 0 0 0 0 0 0 0 July 20 17 6 0 0 2 33 0 0 2 33 August 22 J7 7 0 0 5 71 0 0 5 71 September 22 16 12 1 8 1 8 0 0 2 16 October 5 5 3 0 0 0 0 3 100 3 100* December 29 21 10 0 0 0 0 4 40 4 40

1967 January 26 22 10 0 0 3 33 0 0 3 33 February 27 25 16 4 25 1 6 0 0 5 31 April 35 26 22 11 50 4 18 0 0 15 68 June 40 29 18 11 60 4 22 J 5 16 88 • Lessthanfivefish. substantiate that spawning had occurred, the collection of spent together with ripe fish suggests that it had (Beardsley, 1967).

Nursery Grounds.-Juveniles from 20 to 80 mm long were collected by seine in the mangroves and along the shores of muddy bays. At no time were fish larger than 80 mm taken in these collections. Few specimens less than 50 mm were collected by trawl in the bay samples. The trawl used would, however, have taken fish as small as 20 mm.

Age of Maturation.-The age at maturation was observed to be 18 months (125 mm); however, regression analyses of the various reproductive stages versus length indicated that l1-month-old fish (l00 mm) could be ex- pected to exhibit the ripening or ripe condition (Fig. 6). Fish that were spawned one season could be mature the next season, when J 1 to 13 months old. 892 Bulletin of Marine Science [21(4)

TABLE 2 COMPOSITE DISTRIBUTION OF GONADAL STAGES FOR MATURE (125 MM SL) FEMALES OF Diapterus rhombeus FOR 1966-1967

No. females Total Total over III IV V III-V no. no. 125 mm fish females SL No. 0/0 No. % No. % No. % January 26 22 10 0 0 3 33 0 0 3 33 February 27 25 16 4 25 1 6 0 0 5 31 March 36 29 16 4 25 4 25 1 6 9 56 April 66 34 26 12 45 4 15 2 7 18 67 June 63 47 22 11 50 4 18 1 4 16 72 July 20 17 6 0 0 2 33 0 0 2 33 August 22 17 7 0 0 5 71 0 0 5 71 September 47 30 16 1 6 2 12 1 6 4 24 October 5 5 3 a 0 0 0 3 100 3 100 December 29 21 10 0 0 0 0 4 40 4 40

Efficiency of Spawning.- The displacement volume of spent gonads de- creases with age (Fig. 6). Apparently the younger fish do not release all of their eggs during their first spawning season. After having spawned several times, most eggs are released. The older fish spawn more efficiently by releasing a higher percentage of their eggs. Sex Ratios.-The male-to-female ratios were determined for every month of the year. Females outnumbered the males by a 3-to-l ratio nearly every month. Fluctuations one month were not repeated the following year. The fluctuations did not correspond to the spawning season. This unusual ratio may be explained by bias in the measuring technique, as the sex of fish less than 110 mm was often difficult to determine. Female fish attain a larger size than males; if this is the case with D. rhombeus, then a greater number of those larger than 110 mm would have been females. Growth Rates and Age Determination.-Statistical analyses of growth, using techniques such as the classical von Bertalanffy sigmoid growth equation, necessitate large samples. The samples collected during this study contained from 5 to 40 specimens in the trawl hauls, and from 0 to 177 in the seine hauls. Because of the small size of samples and the fact that neither the length at hatching nor the maximum length attained were known, a less sophisticated technique of analysis was used. 1971] Austin: Biology of the Rhomboid Mojarra 893 .S ..c: .•..<;:'" 0

- Q) OJ)'" c~ Q) •...U Q) Po. 00 \l;) 0'\

-.•..•0 \l;) \l;) 0'\ -E .t:0 ;::-5'" . III ~ -t:lo E E ..:::»0 ••• ,D ~~ ~~ t::>..'" .S Q) I Q.~.•..• ••.•u I- o ;:l -0 Z '"~ 0•... 0 Q)o., E Q) 2 .- •... IIIU..c::u o.,~ '" Q) -"@ .•.. 0 OJ) c:; 'c ~ 0., .•..'" 0 .•..•III 'r;; o o 0 0;0 0., ~ E C\I •... " u0

(A -III S3~'v' .LS)S3l'v' ~3.:l.:JO 39'v'1 N3 Jtl3d vi ~ ~ ;:J 8 ~ 894 Bulletin of Marine Science [21 (4)

I- Z L1l }: L1l U •...•...... :5 "- 0.. -', ,- Vl z:l ..," ".,,~-_ ... )- - cr 05 ~ /~~ o ~ 'It 0·1 .. .. Immaturcz: 90 100 110 1 0 130 140 150mm STANDARD LENGTH

FIGURE 6. Regression analyses between displacement volumes of ovaries and standard lengths for each reproductive stage of Diapterus rhombeus.

Diapterus rhombeus does not exhibit reduced growth during the winter months, and no annuli are formed. A period of reduced growth coincides, however, with the spawning season. This physiological change brings about the formation of a spawning check. Since not all fish of each age- group spawn at the same time, spawning checks were not used as a measurement of age. Monthly modal classes were calculated using statistical techniques (Snedecor, 1959). The first month that a class appeared in the samples was arbitrarily designated as age "1 month," and successive months as age "2 months," "3 months," and so on, until the class disappeared from the samples. The trawl collections which were analyzed fell naturally into three size groups: less than 70 mm, 70 to 100 mm, and over 100 mm. Each of the groups was analyzed separately, using linear regression techniques; the modal lengths from each month (Fig. 7) were used as the "y" coor- dinate, and assigned age as the "x." The three groups were then plotted simultaneously and the calculated lines connected (Fig. 8). Once the slope on the line for the youngest class of fish was calculated and the spawning seasons established, it was possible to affix an age to the various classes using back-extrapolation to "time 0." These calculated ages and the calculated growth were plotted logarithmically; this curve is graphically depicted in Figure 9. The back-extrapolation from the calculated ages to "time 0" showed a good correlation with actual spawning periods. Few fish over 135 mm were collected; only two fish over 160 mm and one over 170 mm were taken. Either the larger fish leave the collection area, or they die, having reached the end of their life span. 1971] Austin: Biology of the Rhomboid Mojarra 895

April

Juna

July

August

Api'll

Juno

Novcmt.cr-2°1 1~0~~~-----~~~17~Omm

STANDARD L::::-.GiH IN r--ulllMET£ns, FIGURE7. Frequency distribution of spawning classes of Diapterus rhombeus, showing empirical growth by months; all lengths are standard lengths.

Food Habits.-The diet of D. rhombeus inhabiting MayagUez Bay, Mayagiiez, Puerto Rico, was determined by size and season (Fig. 10). Small fish, those less than 65 mm, exhibited a seasonal variation in their diet. During the spring and summer, plant material (mostly Cyanophyta) constitutes the single most identifiable item in the diet (30 per cent). Mud, sand, and unidentifiable material made up over 50 per cent of the winter diet, plants composed less than 10 per cent, and microcrustaceans (benthic ostracods and harpacticoid copepods) over 40 per cent. Fish six months to a year old (65-100 mm) exhibited less variability in their diet. During summer months these fish consumed plants primarily (25-30 per cent). However, as with the younger fish, mud comprises over 50 per cent of the volume of the stomach contents. Microcrustaceans re- mained in the diet (lO per cent), and pelecypods were identified in minor 896 Bulletin of Marine Science [21(4)

160

11)140 L b=45 (>I t 120 ~ i 100 .S .c b=9-2 t7.c: 80 (>I ...J 60 '0 L '1l '0 c: 40 .'!l Vl b=slope

4 6 B 10 12 14 16 18 20 Age in Months

FIGURE 8. Combined regression analyses for small (to 70 mm), medium (70 to 100 mm), and large (over ]00 mm) specimens of Diapterus rhombeus. Standard length versus age in months.

200

150

:I 50 b=6'5 x=l y.,12·7

10 1 2 5 10 20 30

Age in Months

FIGURE 9. Logarithmic regression for all sizes of Diapterus rhombeus. Stan- dard length versus age in months. 1971] Austin: Biology of the Rhomboid Mojarra 897

SPRING SUMMER 100'/. 100'/

MUD 75 MUD 75 ~ AND : , UNIDENTIFIED AND , , I UNIDENTIFIE'D I I , . , , , 50 ! l : 50 ! , : , : I I PLAN T , 25 , 25 MATERIAL : MATERIAL ,!

·65 65 - 100 101-135 .135mm < 65 65-100 101-135 .135mm

100'/. 100'/.

I I ,I I 75 I AND i UNIDENTIFIED

50 50 AND MUD PLANT, 25 ! 25 : MATERIALS , ., , , i (65 8'-100 101- 135 .'35mm .65 65-100 101-135 .135mm FIGURE 10. Seasonal variations in diet, according to size of specimens of Diapterus rhombeus. amounts (5 per cent). During the winter there was no substantial reduc- tion in the amount of plant material ingested, although much of the Cyanophyta was replaced by spermatophytes. Copepods and ostracods doubled in volume (25 per cent) with a reduction in the percentage of mud (40 per cent). Adult fish, a year to a year and a half in age (101-135 mm), fed pri- marily upon plant material, in the form of spermatophytes (Thalassia and Halophila), and upon pelecypods and polychaetes. During the summer, plants comprised over 40 per cent, and during the winter, 50 per cent, of their diet. During summer, pelecypods (Tellina and Yoldia) and errant polychaetes made up to 25 per cent of the diet, followed by mud and sand, which displaced the other 30 per cent. An occasional crustacean was found, but not enough to be considered a significant portion of the sum- mer diet. 898 Bulletin of Marine Science [21(4) TABLE 3 FOOD HABITS OF Diapterus rhombeus, MAYAGUEZ BAY, MAYAGUEZ, PUERTO RICO, ALL SIZES AND SEASONS, FROM MARCH 1966 THROUGH SEPTEMBER 1967 (N = 95)

%, by volume, % of total no. fish of item in diet containing item

PLANT MATERIAL 35.23 42.8 Chlorophyta RhizocLonium riparium Cyanophyta Lyngbya majuscula Rhodophyta Polysiphonia sp. Spermatophyta Thalassia testudinum Halophila sp. Ruppia maritima Bryophyta Leucobyum albicium

MUD, UNDIGESTED MATTER AND DIGESTED MATERIAL 45.8 90.5

MOLLUSCA 6.6 34.0 Pelecypoda Yoldia proprotracta Tellina sp. Corbula disparilis Chione cancellata Gastropoda 0.1 0.9

ANNELIDA 3.07 18.0 Polychaeta Errantia Syllidae

CRUSTACEA 8.09 34.6 Ostracoda Copepoda Harpactacoida Decapoda Natantia Penaeidae Brachyura Portunidae Anomura Paguridae Tanaidacea 1971] Austin: Biology of the Rhomboid Mojarra 899 TABLE 3 (Continued)

%. by volume, % of total no. fish of item in diet containingitem

COELENTERATA AND CTENOPHORA 1.10 2.7 Hydroidea

PROTOZOA 0.05 1.5 Sarcodina Foraminifera

MISCELLANEOUS 0.1 1.1 Insect pupa Mammalian hairs

EMPTY 3.8

The amount of mud, sand, and plant material ingested remained about the same in winter as in the summer. During winter, the pelecypods and polychaetes were almost completely replaced by crustaceans, including penaeid shrimp, and portunid and pagurid crabs. This change is un- doubtedly due to seasonal changes in the benthic fauna. The year-and-a-half- to two-year-old fish exhibited essentially the same summer diet as the year-old fish. Their winter diet, however, showed an increase in the number of polychaetes eaten, with a decrease in the number of crustaceans. The amount of plant material and mud ingested remained about the same throughout the year. Plant material becomes an increasingly important part of the diet as the fish grows. The microcrustaceans which are an integral part of the ingested material in small fish are replaced by polychaetes and pelecypods in the older fish. Figure 11 shows an hypothetical fish followed through a year's growth and dietary changes. Adults of D. rhombeus are believed to be nocturnal, as the stomachs examined from daytime collections were empty and those from night col- lections were full. The reverse is true, however, for the juveniles. This could be the reason for the dietary differences between the large and small fish. Ecological Notes.-The stomach contents of 109 juvenile and adult piscivorous fish, typical of the mangrove habitats, were examined for juvenile mojarras. Only three, the snook, Centropomus undecimalis; the barracuda, Sphyraena barracuda; and the scorpionfish, Scorpaena grandi- cornis; had eaten D. rhombeus (Table 4). Juvenile mojarras, both D. rhombeus and the spotfin mojarra, Eucinostomus argenteus, are the most 900 Bulletin of Marine Science [21(4)

,..,'> lye PELECYPODS CRU~TACEANS

75

MUD

50 UNIDEN TIFIE 0

25

oc."

FIGURE 11. Dietary changes with growth and season for an hypothetical individual of Diapterus rhombeus. common juvenile fish collected by seine in the mangroves. Despite this abundance of small (20-50 mm) silvery fish, less than a 3 per cent occur- rence of predation on them was found in the potential predators which were studied. Adult specimens of Diapterus rhombeus; the Irish pompano, D.

TABLE 4 PREDATION ON JUVENILE (LESS THAN 50 MM) GERREIDAE BY YOUNG CARNI- VORES IN THE MANGROVES, MAYAGUEZ, PUERTO RICO

No. specimens No. containing % gerreids Carnivores and size-range gerreids % in contents Negaprion brevirostris reported Megalops atlanticus 6 (153-220 mm) none* Elops saurus 10 (147-174 mm) none Centropomus undecimalis 53 87-223 mm) 1 1.8 12.5 Sphyraena barracuda 17 61-331 mm) 5.8 50.0 Lutjanus apodus 22 54-103 mm) none Scorpaena grandicornis 86 mm) 1 100 100 Totals 109 3 X = 2.7%

• However, reported by Erdman (1958). [971] Austin: Biology of the Rhomboid Mojarra 901 TABLE 5 PERCENTAGE DISTRIBUTION OF SPECIES OF Diapterus, BY ENVIRONMENT

Diapterus Diapterus Diapterus rhombeus olisthostomus (Eugerres) plumieri (% ) (% ) (%) Open bays (salinity ~ 351c,) 99.5 0.4 0.1 Mangroves, channels enclosed bays (salinities 351,,-201,,) 33.0 49.0 18.0 Freshwater channels, lakes, streams (salinities < 20~{o) 12.5 25.0 62.0 (all juveniles)

Total number of fish examined was 1181. olisthostomus; and the striped mojarra, D. (Eugerres) plumieri have essentially the same food habits (Austin, manuscript), yet interspecific competitIOn is reduced, as D. plumieri lives in waters of relatively low salinity (less than 20%0), D. olisthostomus in salinities between 20%0 and 35%0 in the mangrove channels and river mouths, and D. rhombeus in open muddy bays, where the salinity is over 35%0 (Table 5).

SUMMARY Several aspects of the basic biology of the rhomboid mojarra, Diapterus rhombeus Cuvier, were studied, including the reproductive biology, growth rates, age, and food habits. The spawning season extends from January to September, with a period of peak activity during the early spring and again in midsummer. These periods were determined on the basis of analyses of the gonadal displacement volumes, diameters of ova, spawning marks on scales, and juvenile growth rates. The spawning grounds appeared to be in the deep-water part of their habitat. The nursery grounds are the shallow waters along the muddy beaches and in the mangrove channels. The age at maturation was observed to be 18 months; calculations in- dicated, however, that 11- to 13-month-old fish are capable of spawning. Males and females appeared in a I-to-3 ratio all year. Growth of D. rhombeus averaged 10 mm per month in juveniles less than 70 mm long. In fish between 70 mm and 100 mm long, it averaged 9 mm per month. Fish over 100 mm but less than 150 mm grew at a reduced rate of 5 mm per month. Too few fish over 150 mm were collected to permit any statistical calculations of growth. Age was determined on the basis of back-extrapolation of calculated 902 Bulletin of Marine Science [21 (4) growth to known spawning periods. Fish 60 mm long are 6 months old; 100 mm, 10 to 12 months old; and 150 mm, 20 to 24 months old. No fish over 175 mm was collected. The life span of D. rhombeus may be inferred as two years, based on the data of this study. Small (65 mm) fish in Mayagiiez Bay and among the estuarine mangroves of southwest Puerto Rico fed principally upon plants and microbenthic crustaceans. Mud comprised a large percentage of the stomach contents. Fish in the 65- to 135-mm range consumed plants, crustaceans, and pelecy- pods primarily. Mud was a large contributor to the total content. Large mojarra (over 135 mm) fed primarily on plant material, pelecypods, and polychaetes. Despite their concentrations in the mangrove canals, few young (20-50 mm) mojarras are eaten by piscivorous fish. From their size and silvery appearance, one would expect that they would constitute a significant pro- portion of the diet of predatory mangrove fish, yet only a two per cent incidence of such predation was measured in the stomach analyses of the fish examined.

SUMARIO ALGUNOS ASPECTOS DE LA BIOLOGiA DE LA MOJARRA ROMBOIDE Diapterus rhombeus EN PUERTO Rico La mojarra romboide, Diapterus rhombeus Cuvier, es un pez que ge- neralmente se encuentra en fondos blandos en el suroeste de Puerto Rico. La epoca de desove es larga, durando desde enero hasta septiembre y la ma- durez tiene lugar a la edad de 11 a 13 meses. EI crecimiento es lineal en los peces j6venes hasta los 70 mm (7 meses). Su promedio de crecimiento es 10 mm/mes. Los peces de 70-100 mm de longitud (12 meses) crecen a un promedio de 9 mm/mes. Despues de un ano el crecimiento baja a 5 mm/ meso La dieta consiste de plantas, pelecfpodos, crustaceos y poliquetos; el fango tambien constituye un gran por dento del contenido estomacal. £1 crecimiento y cambios de estaciones estan reflejados por cambios en la dieta.

LITERATURE CITED AUSTIN, HERBERT M. 1971. The feeding habits of some juvenile marine fishes from the mangroves of western Puerto Rico. Caribb. J. Sci., 11 (2-3). BEARDSLEY, GRANT L. 1967. Age, growth and reproduction of the dolphin, Coryphaena hippurus, in the Straits of Florida. Copeia, 1967 (2) : 441-451. BREDER, CHARLES M., JR. 1934. Ecology of an oceanic freshwater lake. Zoologica, N.Y., 8(3): 70-73. 1945. Field book of marine fishes. Pp. 186-189. G. P. Putnam's Sons, New York, 332 pp. 1971] Austin: Biology of the Rhomboid Mojarra 903

DE SYLVA, DONALD P. 1963. Systematics and life history of the great barracuda, Sphyraena barracuda (Walbaum). Stud. Trop. Oceanogr., Miami, No.1: viii + 179 pp. ERDMAN, DONALD R. 1958. Foods of pelagic fishes from Puerto Rico and the Bahama Islands. Proc. 3rd International Game Fish Conference, Miami Beach, Florida, p. 9. 1967. Inland gamefishes of Puerto Rico. Spec. PubIs., P.R. Dept. Agric .• San Juan, P.R., 66 pp. EVER MANN, BARTON W. AND MILLARD C. MARSH 1902. The fishes of Porto Rico. Pp. 204-211 in Bull. U.S. Fish Commn. for 1900,20, 350 pp. GUNTER, GORDON 1957. Predominance of the young among marine fishes found in fresh- water. Copeia, 1957(1): 13-16. GUNTER, GORDON AND G. HALL 1963. Additions to the list of euryhaline fishes of North America. Copeia, 1963 (3): 596-597. HILDEBRAND, SAMUEL F. 1939. The Panama Canal as a passageway for fishes and invertebrates observed. Zoologica, N.Y., 24(1-5): 15-46. MANNING, RAYMOND AND DURBIN C. TABB 1961. A check list of the flora and fauna of northern Florida Bay and adjacent brackish waters of the Florida mainland collected during July, 1957 through September, 1960. Bull. Mar. Sci. Gulf Caribb., 11 (4) : 552-649. NICHOLS, JOHN T. 1929. The fishes of Porto Rico. Scient. Surv. P. Rico, 10; 161-295. SCHULTZ, LEONARD P. 1949. A further contribution to the ichthyology of Venezuela. Proc. U.S. natn. Mus., 99(3235): 1-211,20 figs, 3 pIs. SNEDECOR, GEORGE W. 1959. Statistical methods, applied to experiments in agriculture and biology. Iowa State College Press, Ames, Iowa, 534 pp.