Bluefish, continued 



Growth and Development 



Egg Size and Embryonic Development : Fertilized eggs 

 are 0.90-1 .20 mm in diameter, with a single oil globule 

 present 0.22-0.30 mm in diameter (Deuel et al. 1966, 

 Lippson and Moran 1 974). The egg capsule is thin, but 

 tough, and is transparent and colorless. Yolk is a pale 

 amber and the oil globule is a deeper amber. Perivi- 

 telline space is about one sixth the egg radius. Devel- 

 opment is oviparous and cell division proceeds rapidly. 

 Regular movements are first noticed about 37 hours 

 after fertilization (AF) with mass hatching occurring 

 between 44 to 46 hours AF at 18.5 to 22.2°C, and 46 

 to 48 hours AF at 18.0 to 22.2° (Deuel et al. 1966, 

 Lippson and Moran 1974, Norcross et al. 1974). Egg 

 incubation time at 25° C has been estimated at 30 to 36 

 hours (Ditty and Shaw 1995). 



Age and Size of Larvae : Newly hatched larvae are 2.0- 

 2.4 mm total length (TL) and grow to 2.9 mm TL during 

 their first day. The yolk sac is absorbed by about 4 mm 

 TL. Incipient fin rays are evident by 6 mm TL, and 

 countable by 8 mm TL. Fin development is complete 

 by 1 3 to 1 4 mm TL marking the end of the larval stage 

 (Deuel et al. 1 966, Lippson and Moran 1 974, Norcross 

 etal. 1974). 



Juvenile Size Range : The minimum length of this stage 

 is about 1 4 mm SL (Lippson and Moran 1 974, Norcross 

 et al. 1974). Maturity occurs during the second year 

 when fish are about 300 to 350 mm fork length (FL) 

 (Deuel et al. 1966). A 200 mm TL female with nearly 

 mature eggs was reported from Mexican waters 

 (Hildebrand 1957). Testes mature slightly earlier than 

 ovaries in fish of similar size (Wilk 1977). 



Age and Size of Adults : In the Gulf of Mexico, adult 

 bluefish have been estimated up to 8 years old, and up 

 to 767 mm FL (Barger 1 990), based on otolith analysis. 

 Initial growth in the Gulf of Mexico is considered to be 

 rapid. Barger (1990) provides VonBertalanffy growth 

 parameters for Gulf of Mexico and southeast U.S. 

 bluefish. On the U.S. east coast, bluefish up to 9 years 

 old have been aged through scale analyses, but larger 

 and presumably older fish have been reported that 

 may be as old as 14 years (Wilk 1977). Sizes for 

 different year classes range as follows; 230 mm FL at 

 1 + year; 400 mm FL at 2+ years; 490 mm FL at 3+ years 

 (1 .81 6 kg); 580 mm FL at 4+ years (3.1 78 kg); 640 mm 

 FL at 5+ years (4.086 kg); 690 mm FL at 6+ years 

 (4.540 kg); and 71 mm FL at 7+ years (5.448 kg) (Wilk 

 1977). A size of about 860 mm FL and 8.455 kg is 

 suggested for fish reaching 14 years of age (Wilk 

 1977), and a fish caught in North Carolina waters 

 weighed 14.40 kg (IGFA 1991). 



Food and Feeding 



Trophic Mode : The bluefish is a voracious, pelagic, 

 marine predator that visually feeds on a variety of 

 fishes and invertebrates throughout the water column 

 (Olla et al. 1970, Olla and Studholme 1972, Benson 

 1982). It has earned nicknames such as "marine 

 piranah" and "chopper" because fish will move in large 

 schools through shoals of bait fish in a feeding frenzy 

 (IGFA 1991). Schools of bluefish can be located at a 

 distance by hovering seagulls that are eating forage 

 fish driven to the surface by feeding bluefish (Olla et al. 

 1970). During these feeding frenzies, bluefish are 

 known to even strand themselves on shore while in 

 pursuit of prey that have fled inshore (IGFA 1 991 ). 



Food Items : Larval and early juvenile bluefish feed 

 mostly on copepods, and gradually shift to fish and 

 crab larvae (Marks and Conover 1 993). Copepods are 

 the most common prey type in fish <60 mm TL. Crab 

 larvae are initially consumed by bluefish < 40 mm TL, 

 while the onset of piscivory occurs in the 30-70 mm TL 

 size range. As bluefish grow, they tend to consume 

 increasingly larger teleost prey. The shift in food items 

 corresponds to the period of inshore migration, making 

 the change in diet coincident with a habitat shift (Marks 

 and Conover 1 993). The prey of adult bluefish include 

 annelid worms, mysids, shrimps, crabs, lobsters, squid, 

 lampreys, small sharks, eels, herrings, anchovies, 

 killifishes, silversides, halfbeaks, bluefish, pipefish, 

 sciaenids, jacks, flatfish, searobins, mackerels, mul- 

 lets, cods, sea bass, porgies, wrasses, puffers, butter- 

 fish, sand lances, cusk-eels, lizardfish, and eelpouts 

 (Miles 1949, Richards 1976, Benson 1982). Bluefish 

 feeding activities drive prey species near the waters 

 surface, where they are vulnerable to predation by 

 piscivorous birds (Safina 1990a, Safina 1990b). 



Biological Interactions 



Predation : Only such large predators as sharks, tunas, 

 swordfish, and wahoo pose threats to these fast swim- 

 mers (Medved and Marshall 1981). 



Factors Influencing Populations : Fin rot has been 

 noted as a disease to which this species is particularly 

 vulnerable. Known parasites include isopods, copep- 

 ods, cestodes, trematodes, nematodes, and protozo- 

 ans (Wilk 1977). 



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