Silversides, continued 



M. peninsulae extended from February to July, with 

 peaks March through June, at temperatures 16.7 to 

 30.8°C (Middaugh and Hemmer 1987a). Spawning 

 activity peaked during "equatorial tides", when tidal 

 height and current were at their minima, possibly an 

 adaptation to enhance fertilization success. Spawning 

 occurred in shallow water, 10 - 60 cm deep, and 

 spawned eggs adhered to the red algae Ceramium 

 byssoideumover rocky substrate (Middaugh and Hem- 

 mer 1987a). 



Fecundity : Silversides are fractional spawners that 

 spawn several times per season, and sometimes all 

 year (Hildebrand 1922, Hellier 1962, Fisher 1973). 

 Female Menidia beryllina in one study deposited 1 to 

 20 eggs in a single spawning pass, and were not 

 observed to repeatedly broadcast eggs. Females 

 stripped of ripe eggs yielded 10 to 200 eggs per 

 individual (Fisher 1 973). Fecundity is size dependent, 

 with average sized females (standard length (SL) 75 

 mm) producing approximately 835 eggs daily, large 

 females about 2000 eggs, and small females about 

 200 eggs. Over a spawning period of 91 to 1 22 days, 

 an average sized M. beryllina female has the capacity 

 to produce 75,985 to 101,879 eggs, a large female 

 1 32,860 to 1 78,21 eggs, and a small female 45,000 to 

 61 ,000 eggs (Hubbs 1 982). Spawners are usually age 

 class-1 fish, but class-0 fish have been found to spawn 

 occasionally (Fisher 1973, Hubbs 1982). 



Growth and Development 



Egg Size and Embryonic Development Eggs of Menidia 

 beryllina are demersal with gelatinous threads that 

 attach to vegetation, other objects, and to each other 

 on or near bottom (Hildebrand 1 922, Martin and Drewry 

 1 978). They have a clear yellowish appearance with a 

 large oil globule occupying a central position and 

 variously distributed smaller globules ranging from a 

 few to several (Hildebrand 1922, Hubbs 1982). The 

 chorion has a tuft of 4 to 9 adhesive filaments one of 

 which is enlarged and much longer than the others, 

 about 30 to 50 mm in total length. Eggs are not quite 

 spherical when first spawned and range about 0.75 to 

 1.0 mm in diameter (Hildebrand 1922, Martin and 

 Drewry 1 978). Cleavage is meroblastic and equal with 

 the second cleavage at right angles to the first (Martin 

 and Drewry 1978). Hatching occurs in 10 days at 

 27.5°C and 5 days in warmer temperatures (Hubbs et 

 al. 1971, Hubbs 1982). Larvae are present through the 

 spring, and in summer and fall months (Martin and 

 Drewry 1978). 



Age and Size of Larvae : Menidia beryllina larvae are 

 about 3.5-4.0 mm TL at hatching (Hildebrand 1922, 

 Martin and Drewry 1 978). They have an oval yolk sac 

 with a single oil globule in the anterior end. In a 

 laboratory feeding experiment, yolk depletion and star- 



vation occurred in 3 to 4 days at 30°C, and 2 to 3 days 

 at 1 5°C (Hubbs et al. 1 971 , Martin and Drewry 1 978). 

 The body is elongate and slender with an extremely 

 short gut and an anus about 1 /4 of way from tip of snout 

 to rear of caudal finfold (Martin and Drewry 1978). 

 They are highly transparent with 3 to 1 1 melanophores 

 on the dorsal surface of the head, and a cluster above 

 the gut and dorsal surface of the yolk. At 7.8 mm TL, 

 about 15 caudal rays and 8 anal ray bases become 

 visible. The first dorsal fin is rudimentary and other 

 median fins have a full complement of rays tending 

 toward the adult fin shape. The pelvic fins are formed. 

 Larvae are aggregating by 8 to 1 mm TL, and school- 

 ing by 1 1 to 1 2 mm TL. The first dorsal fin is formed by 

 11 to 1 2 mm TL(Martin and Drewry 1 978). The end of 

 this stage is at about 11 to 1 2 mm TL (Garwood 1 968, 

 Martin and Drewry 1978). 



Juvenile Size Range : In Mississippi Sound, the size 

 range for juvenile stage Menidia is about 1 2 to 49 mm 

 TL (Garwood 1 968). Length-frequency data are unre- 

 liable for a growth estimate, but one study of Menidia in 

 Tampa Bay indicated 5-7 mm per month from June to 

 November, and that early-spawned juveniles grew 

 about 8 mm SL per month from June to September. 

 Lengths of 75 to 85 mm SL were achieved after 1 year 

 of growth (Springer and Woodburn 1960). Winter cold 

 evidently inhibits growth (Martin and Drewry 1978). 



Age and Size of Adults : Silversides may reach sexual 

 maturity by 45 mm TL or 33 mm SL (Hellier 1962, 

 Garwood 1968, Martin and Drewry 1978). Males are 

 smaller than females with average sizes of 50.9 and 

 55.0 mm TL for males and 59.5 and 61 .0 mm TL for 

 females being reported (Hildebrand 1 922, Gunter 1 945). 

 Maturity is usually reached by 1 year, but sometimes as 

 early as 5 months (Martin and Drewry 1978, Hubbs 

 1982). Weight ranges from 0.1 to 7.5 g for fish 15 to 87 

 mm SL with a 95 mm TL fish weighing 1 1 .4 g and a 55 

 mm TL fish weighing 2.84 g (Franks 1 970, Barrett et al. 

 1978). The largest reported size is 125 mm TL 

 (Simmons 1 957). The life span Menidia is usually one 

 year, with some survivals to 2 years (Gunter 1945, 

 Martin and Drewry 1978, Hubbs 1982). Total length 

 (TL) can be estimated from standard length (SL) for 

 silversides by multiplying SL by 1.2 (Hubbs 1982). 



Food and Feeding 



Trophic Mode : Silversides are carnivorous, secondary 

 consumers feeding mainly during daylight hours espe- 

 cially in the early morning with some additional after- 

 noon feeding by adults (Darnell 1 958, Middaugh et al. 

 1 985, Wurtsbaugh and Li 1 985). One study of Menidia 

 beryllina in Louisiana reports equal feeding intensity 

 both day and night (Ruebsamen 1 972). M. peninsulae 

 are reported to feed primarily during the day (Middaugh 

 and Hemmer 1984). Trophic partitioning between 



187 



