Coordinator: Dr. Nadia Pinardi

Workplan

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Subtasks year 1 year 2

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C.2.1 ============ ========

C.2.2 ============

C.2.3 ============ ============

C.2.4 ============

C.2.5 =============

C.2.6 ============= ============

Description of Team

Institution Personnel Position Man/month

IMGA-CNR (1) M.Zavatarelli Scientist 3

To be funded boursary 12

OGS-DOGA (2) A.Crise Scientist 3

ITT-CNR (3) R.Purini Scientist 2

ISDGM-CNR Venezia (4) A.Bergamasco Scientist 2

S.Carniel Scientist 3

C.Zago Scientist 3

METU-Erdemli, Turkey(4) T.Oguz Scientist 1

Financial budget *	Total
1997	90
1998	110
Total	200

*All costs are in Millions of Lire

Budget allocated to each team and detailed explanation of costs

1997 1998

Consum. Travel Personnel Tot. Consum. Travel Personnel Tot.

(1) 20 5 25 30 5 35

(2) 20 5 25 30 5 35

(3) 15 5 20 15 5 20

(4) 20 20 20 20

90 110

Task C.2.2 The effects of variability of marine ecosystems on visual sensitivity of fish

Responsible: Dr.S.Vallerga and S.Archer (CNR, Sezione Ecologia della visione, Oristano)

Background

The visual system of fish is exposed to a wide spectrum of aquatic light conditions ranging from clear blue oceanic water to red stained rivers. The retinal spectral sensitivity of fish exposed to these different conditions becomes tuned into the wavelengths of light available for vision and fish are sensitive to light ranging from the UV to the far-red. Thus fish that live in deep ocean water are mainly sensitive to blue light whereas fish that live in coastal water are more green sensitive (Vallerga 1994). Within these broad ranges there is also fine tuning to suit particular micro-habitats and species specific behavior. Migratory fish that move between different water environments can change their visual sensitivity to match each environment. Some freshwater fish experience natural seasonal changes associated with cycles in the growth and decay of plant matter and can become more or less green-sensitive at different times of the year. The larvae of many species live in surface waters where there is a broad spectrum of wavelengths to be sampled for vision but develop a more restricted visual sensitivity when they mature and move to deeper water.

Studies of the adaptation of the fish visual system have demonstrated that adaptation can occur very quickly within individual fish. Retinal visual pigments contain a light sensitive chromophore that is derived from either vitamin A1 or vitamin A2. Switching from one chromophore to the other shifts the maximum spectral sensitivity of the visual pigment by a fixed amount and it is possible for the retina to contain ratios of each chromophore giving rise to intermediate sensitivity. This mechanism is used by fish that migrate between coastal water and estuaries/lagoons/rivers to shift their sensitivity to the higher wavelengths normally associated with brackish or freshwater. A sliding ratio of A1 and A2 chromophores is also used by some freshwater fish to stay in tune with seasonal changes in water color due to increases in dissolved chlorophyll and tannins. The visual pigment also has a protein component called opsin. The structure of opsin and its interaction with the chromophore can also change the spectral sensitivity of the visual pigment. It is undoubtedly mainly this relationship that evolution has worked upon to produce the wide range of visual pigment sensitivities that have enabled fish to adapt their visual systems to life in different underwater environments (Archer 1995).

Because we already know that fish can become highly adapted to different or variable water colors it is reasonable to expect that if the color of a particular body of water is variable over time then the visual sensitivity of fish should also become variable or adapted. One part of this project will compare the visual sensitivity of the same fish species taken from clear coastal water and an area of coastal water that often becomes highly stained with chlorophyll to determine how variability of the environment is affecting visual sensitivity.

It is now known that fish can be sensitive to UV light and UV sensitivity has been discovered in salmon, pollack, dace, trout, goldfish, perch, guppies, zebrafish and goldfish. It seems unusual for us that UV should be used for vision but there is no physical or biological reason why long-wave UV light cannot be used to form images. However, UV light does not penetrate water very deep and is more prone to scatter than longer wavelengths which means that it is probably only used for vision in surface waters over short distances. Investigations so far indicate that UV sensitivity may be quite common in larval fish which tend to live in surface water. Larval salmon, trout and pollack all have UV sensitivity when they live at the surface but this is lost when they mature and move deeper (Shand et al. 1988). It is possible that the larvae are using the UV light available in the surface water to detect planctonic food. A significant amount of biological effort is required to manufacture these UV sensitive visual pigments and we must assume that in these larvae sensitivity to UV light is important during early development. The larval stage is a critical period for survival and is the period when most fish mortality occurs. We are now aware that ozone content in the atmosphere above the Mediterranean is being reduced and this will lead to increased levels of UV irradiation (ref). If the levels of UV light reaching the water surface increase significantly this could influence UV vision and behavior in surface living larval fish. The second part of this task will investigate the occurrence of UV visual sensitivity in larval fish to create a database of Mediterranean fish species that are sensitive to UV. This database will make it possible to examine future correlations between changes in UV light levels and the effects upon vision and behavior in larval fish.

Scientific Objectives

a) The effect of algal blooms on visual sensitivity

Fish species will be collected from coastal areas in the Adriatic which suffer from algal blooms. The water in these areas is much more green than usual due to the large amount of dissolved chlorophyll. The same fish species will also be collected from clear coastal water around Sardinia. Using spectrophotometric techniques we will measure scotopic visual sensitivity of visual pigments extracted from the retina of these fish (Archer et al. 1996). The species will be chosen to include species that are able to alter their A1/A2 chromophore ratio and others that only utilize an A1 chromophore. The former species will show us if the variable A1/A2 mechanism is being used to provide fast seasonal adaptation and the latter will indicate if any evolutionary based genetic adaptation has occurred via the opsin protein. Fish will be sampled during different periods of the year so that potential temporal adaptation to the greener water during algal blooms can be detected. The inter-comparison between species sampled from the Adriatic and Sardinia will highlight any visual sensitivity adaptation that is being influenced by the blooms.

b) Creation of a database of UV sensitivity in larval fish

Larval fish from a wide range of Mediterranean species will be collected from Sardinian coastal and lagoon water. The fine structure of the retina of these fish will be examined histologically to detect the presence of UV sensitive cone photoreceptors which because of their size are morphologically distinguishable from other photoreceptors and occupy distinct positions in the retinal photoreceptor array. We will use the technique of microspectrophotometry which combines a scanning spectrophotometer with a high power microscope and enables the absorbance spectra of single cells to be measured (Archer et al. 1987). This technique will be used to measure the absorbance spectra of the UV sensitive visual pigments in single photoreceptors in retinal preparations from the larval fish. In this way we will create a database of Mediterranean fish species whose larvae posses UV sensitive photoreceptors.

Workplan

1. Collect key species from high algal bloom areas of the Adriatic coast and clear water areas of the Sardinian coast.

2. Identify from histology the presence of UV sensitive photoreceptors in the retina.

3. Measure scotopic visual sensitivity in retinal extracts from these species and compare to determine if visual sensitivity adaptation has occurred.

4. Collect larval fish of a wide range of marine species in Sardinian coastal and lagoon water.

5. Measure UV sensitivity in larval fish retinas using microspectrophotometry.

Description of team

Institution Personnel Position Man/month

ICB-CNR S. Vallerga Scientist 1

(Sez. Ecologia S. Archer Scientist 5

della Visione) E. Loew Visiting Professor 2

To be funded Ph.D student 19

Financial budget *	Total
1997	45
1998	45
Total	90