Relationships between maternal size, egg diameter, time of spawning season, temperature, and length at hatch of Atlantic silverside, Menidia menidia

Eggs were stripped from gravid Atlantic silversides collected on two occasions, once during the early part and once during the late part of the natural spawning season. Unfertilized egg diameter was not correlated with length of the female, nor was it significantly larger during the early part of the season. Eggs were fertilized and incubated in the laboratory. Larval length at hatch was measured every 24 h during the hatching period after embryos were incubated at 18 or 25° C. Lower incubation temperature caused a significantly greater length at hatch for the offspring of each of the 20 females studies. In most cases (17 out of 20 at 25° C, 10 out of 20 at 18° C), there was a significant decrease in length at hatch during the hatching period for a given female's eggs incubated at a given temperature. In the natural environment, larvae hatched early in the season under cooler temperatures could average 12% longer than those hatched later under warmer temperatures, and therefore may have a greater chance of survival. The results help to explain the observation that field-caught M. menidia that hatched early in the season are larger at any given age than those that hatched late in the season.