Effects of photoperiod and temperature on the regulation of the onset of maturation in the estuarine fish Menidia

Menidia beryllina (Cope) is an annual species that inhabits coastal estuaries along the east coast of the United States from Cape Cod to the Gulf of Mexico. In Rhode Island, USA, its peak spawning time and the duration of the spawning vary among years and estuaries. However, the onset of gonadal maturation is more consistent (early May), suggesting that it may be regulated by more consistent cues than those regulating spawning. To determine the effects of photoperiod and temperature on the regulation of the onset of maturation two laboratory experiments were conducted and the results compared to field observations. In the first experiment, fish collected from the field in February were exposed to each of four treatments: increasing photoperiod/ increasing temperature; increasing photoperiod / low temperature; low photoperiod/ increasing temperature; and low photoperiod/ low temperature. Only fish exposed to both increasing photoperiod and increasing temperature were able to complete maturation. Fish exposed to low photoperiod and increasing temperature responded by enlarging their livers, a response that was also observed in field fish collected in the fall. Fish exposed to the remaining two treatments neither matured their gonads nor enlarged their livers. In the second experiment fish collected from the field in early March were exposed to three treatments with different photoperiod regimes (daylight constant at 9.5 h, increasing up to 12 h, or increasing up to 15 h) and one increasing temperature regime. Fish in the 9.5-h treatment initiated maturation but were not able to complete the process, those exposed to the 12-h photoperiod matured and spawned for a short period of time before the gonads began to regress, and those exposed to the 15-h photoperiod matured and spawned large numbers of eggs throughout the remainder of the experiment. The 9.5and 12-h photoperiod exposures also resulted in accumulation of reserves in the liver in both females and males. The 15-h photoperiod treatment resulted in liver enlargement in females, which were undergoing vitellogenesis, but not in males. Males exposed to the 9.5and 12-h photoperiod *Corresponding author. Department of Fisheries, Animal and Veterinary Science, University of Rhode Island, Kingston, RI 02881, USA. Tel.: 1 1-401-874-2668; fax: 1 1-401-874-4017. E-mail address: [email protected] (D.A. Bengtson) Present address: US EPA, NHEERL, Atlantic Ecology Division, Narragansett, RI 02882, USA. 0022-0981/99/$ – see front matter  1999 Elsevier Science B.V. All rights reserved. PI I : S0022-0981( 99 )00064-7 286 M. Huber, D.A. Bengtson / J. Exp. Mar. Biol. Ecol. 240 (1999) 285 –302 accumulated significantly more visceral fat than those exposed to the 15-h photoperiod. In females, the amount of visceral fat accumulated was inversely proportional to the hours of light. These findings suggest that this species has evolved mechanisms that enable it to anticipate the coming of winter as well as the coming of suitable breeding conditions and ensure that it exhibits the appropriate response at the appropriate time (reserve accumulation for the winter or gonad maturation in the spring).  1999 Elsevier Science B.V. All rights reserved.