The effect of photoperiod and light intensity on growth and maturation of Atlantic cod in the Bay of Fundy

Description

During 2001-2003 an ACRDP study (Harmon et al. 2003) was conducted to assess the effects of photoperiod on growth and maturation of Atlantic salmon in the Bay of Fundy. The early maturation rate in control cages was 21.5%. Cages where lights were turned on in November had 1.1% mature. The cost of purchasing, wiring and operating the lights was less than $5,000 per cage. The savings gained was greater than $100,000 per 70 m cage. With these impressive results, it is of interest to determine whether photoperiod manipulation on sea cages can be successfully applied to other finfish in Atlantic Canada.

In preliminary trials, early maturation in pre-market Atlantic cod affects ~100% of fish in sea cages, and this problem is not isolated to the Bay of Fundy. Thus, the maturity problem for cod is worse than for salmon. Repeated maturation of individual fish may occur before marketing as males may achieve sexual maturity at age 1 yr (0.3 kg) and females at age 2 yr (1.5 kg), though fish are marketed at age 3 yr (~2.7 kg). Coincident with maturation and shedding of gametes in sea cages is a seasonal 25% weight loss in females and 12% in males. Appetite loss also occurs during spawning which leads to slower growth. During spawning and afterwards, fillets become 'jellied' (high water content) and are reduced in market value. This study will evaluate a method to decrease early maturation.

Other problems also exist with regard to light. Groundfish such as cod inhabit waters of 100 m depth (common range 30-300 m) where light intensity is very low. Species-specific differences exist in the production of "sunscreen", yet no investigation has been undertaken to examine levels of sunscreen in a gadoid species such as cod. The molecules necessary for synthesis of "sunscreen" are obtained directly from the diet, and thus fish fed on artificial diets may be more susceptible to UV radiation than wild fish. Use of shade cloth on sea pens may be necessary to inhibit stress due to UV radiation for groundfish such as cod.

The primary objectives are:

• To adapt technology proven for species such as Atlantic salmon (Hansen et al. 1992) to Atlantic cod.
• To examine the degree of suppression of maturation in both sexes in pre-market and market fish.
• To examine the potential for somatic growth enhancement in light treatments.
• To examine "sunscreen" production and possible use of shade cloth in connection with 24 h lights.

Program Name

Aquaculture Collaborative Research and Development Program (ACRDP)

Year(s)

2004 - 2007

Ecoregion(s)

Atlantic: Gulf of Maine, Scotian Shelf

Principal Investigator(s)

Edward Trippel
Email: Ed.Trippel@dfo-mpo.gc.ca