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Larviculture:
A comprehensive account of research activities of Aqua Research Lab
  1. Carp Culture

    The Carp species likeCatla catla (catla), Labeo rohita (rohu), Cirrhinus mrigala (mrigal), Cyprinus carpio (common carp), Hypophthalmichthys molitrix (silver carp) and Ctenopharyngodon idella (grass carp) are extensively used in composite culture in India. So far there is no research based development package for these species. Hence, we attempted to generate knowledge for larviculture, giving emphasis on larval nutrition and husbandry.

  2. Environmental Requirements

    2.1 Aquahouse

    Immediately after hatching, poorly developed larvae are highly susceptible to environmental stress. Use of excess amount of artificial diets and fish excreta result into
    Aquahouse (front view)
    Fig. 1. Aquahouse (front view)
    deterioration of water quality within the fish culture system. Discharge of this water into the natural environment leads to the environmental degradation. This results into ban on coastal zone aquaculture by honorable Supreme Court of India. In order to maintain optimal environmental conditions for the tiny, sensitive larvae as well as for adult fishes a suitable “Aquahouse’’ has been designed and constructed in the Department of Zoology with the financial support of I.C.A.R., India. The Aquahouse is made of polycarbonate sheet, which helps to maintain the temperature the most critical factor for growth (Fig. 1). It also helps to avoid fluctuations of temperature during hot summer/severe winter. This is most effective for broodstock maintenance and for the culture of high-valued and endangered species.

    2.2.Recirculating system

    Water quality plays a major role in the sustainable development of aquaculture. Feeding of fish with protein rich diets leads to water quality deterioration in terms of higher ammonia and nitrite levels. To overcome this problem and to maintain water quality we tested recirculating system. In the recirculating system the same water is repeatedly used for long time after treatment. In the recirculating system, we used biological filters that converted the harmful ammonia and nitrite to less

    Fig. 2. Innerside of the Aquahouse showing three sets of recirculating systems. PFS = pebbles filter system, HS = hydroponic system, EPFS = earthen pot filter system, S = temperature sensor, T = fish culture tank.
    toxic nitrate and thus succeeded to use the same water for a long time. Various types of biological filters like pebbles filter, earthen pot filter and plant filter (hydroponic system) were used separately or in different combinations (Fig. 2). These reduce ammonia, nitrite (most critical factors of fish growth), phosphate and COD levels in the culture systems (Sharma and Chakrabarti, 1997, 2000). More than 90% survivals of carp larvae were found in this recirculating system. The growth was also faster. In hydroponic system, money plant Pothos spp. (ornamental plant), Lemna major (duck weed, used as raw material for artificial diet preparation of fish) and Trapa spp. (singhara, fruit producing plant) were used as filter bed materials. Thus, the farmers in addition to fish may harvest other useful plant product, which will supplement with additional income. Water requirement for per unit fish production in recirculating system without filtration unit was 1.5 to 2.5-fold higher than recirculating system with filtration unit (Sharma and Chakrabarti, 1997, 1998).
                      Optimization of stocking density is essential to make the system cost-effective and commercially viable. Indian major carps Catla catla, Labeo rohita and Cirrhinus mrigala spawns were cultured under different stocking densities. It appears that the stocking density can be raised up to 8,333/m3. This is 8-fold higher than traditional nursery in India (Sharma and Chakrabarti, 1998, 2003; Sharma et al., 2004). The duration of culture period to get fingerling size is also less than traditional culture system.
     
  3. Digestive Physiology of Carps

    3.1 Scenario during ontogenesis

    A comprehensive analysis of the ontogenic changes occurring during early life stages of the fish is essential for the formulation of artificial diets. Information on the digestive physiology of fish during ontogenesis will ensure fish culturists to develop proper feeding strategies for a particular species. Amylase and proteolytic activities were determined in Indian major carps Catla catla, Labeo rohita and Cirrhinus mrigala and common carp Cyprinus carpio during ontogenic development in relation to natural diet (Chakrabarti and Sharma, 1997; Kumar and Chakrabarti, 1998; Rathore et al., 2005). Amylase activity was very low during transition period from endogenous to exogenous feeding. Enzyme activity increased with age in these species. Bands of various molecular weights appeared during ontogenic development. All these bands expected to correspond to serine proteases with some evidence of increasing proteolytic enzyme activity with the age of fish. High molecular weight bands appeared during early ontogeny and low molecular bands appeared in the later stage of development.

    3.2. Ultrastructure study

    Ultrastructure study of the digestive system showed progressive changes in microvilli, microfilament bundles and secretary granules along with age (Kumar et al., 2000). Ultrastructural study of three different regions of intestine of Cyprinus carpio showed variations. The microvilli increase the digestive and transportive surface and are the structural basis of the processes of membrane digestion. The presence of the granular cytoplasm and minute vacuoles on the apical halves covered by a thin brush-border of columnar epithelial cells of the intestinal mucosa in the present study justified the absorptive function of the cells of anterior region .

    Morphological changes happening in the digestive system of Catla catla during ontogenic development had been documented by Chakrabarti and Singh (2009, unpublished, communicated). The digestive system was simple and straight up to 8th day. Slightly folding was found in 9 DAH catla. Marked folding of the digestive system was found from day-10. Coiling started from day-19 onwards.

    3.3. Digestive enzymes in adult carps

    Characterization of digestive proteases and their efficiency to hydrolyses the proteins of different food ingredients were conducted in three carps Catla catla, Labeo rohita and Hypophthalmichthys molitrix (Kumar et al.,2007 ). The amount of various proteolytic enzymes varied significantly (P < 0.05) in these species. All enzyme extracts, except catla digestive tissue, displayed bell-shaped pH profiles; catla digestive tissue sample had a broad pH activity curve. The effects of various protease inhibitors on enzyme activity showed that enzymes were mainly serine-proteases. Several protein bands ranging from 15.3 to 122.3 kDa were found in enzyme molecular weight of proteases ranged from 22.1-92.7, 25.3-91.2, 21.4-852, 21.7-91.2 and 25.6-90.9 kDa for catla digestive tissue, catla gut contents, rohu digestive tissue, rohu gut contents and silver carp digestive tissue, respectively. Several trypsin and chymotrypsin-like enzymes were observed from each enzyme extract. In vitro digestibility study of various feedstuffs like casein, soybean meal, Silver Cup and Chilean fishmeal showed that all enzyme preparations, except for rohu digestive tissue, had higher degree of hydrolysis for casein than other protein feedstuffs. Enzyme preparations from silver carp digested all feedstuffs more adequately in comparison to other carps.

    3.4 Role of live food in larviculture

    Role of various types of food in carp larviculture as well as in the maintenance of water quality had been evaluated. Comparative studies were performed to evaluate the effects of live food and artificial diet/ refrigerated-plankton food with Cyprinus carpio (Sharma and Chakrabarti, 1999) and Catla catla (Sharma and Chakrabarti, 2009). Feeding of Cirrhinus mrigala larvae with artificial diets varying in quantity of protein (30, 40 and 50%) revealed that incorporation of 40% protein in artificial diet was optimum for growth and survival of larvae (Chakrabarti and Kumar, 2001).

  4. Live Food

    4.1. Culture and biochemical composition

    One of the major obstacles for the advancement of intensive aquaculture of finfish is the acceptance of diets during early life stages. Larval nutrition relies on feeding with live food during the first few days. Monoculture of Ceriodaphnia cornuta by using organic manures shows that the lower dose of organic manures can be used to obtain faster peak, whereas the application of higher dose helps in the production of larger number of Ceriodaphnia cornuta, which sustains longer duration (Srivastava et al., 2006).

    Phospholipid fraction is extremely critical for the larval growth. The commonly available Phosphatidic acid (PA), Phosphatidylethanolamine (PE), Phosphatidylcholine (PC), Phosphatidylserin (PS), Phosphatidylinositol (PI) and Cardiolipin (CAR) were quantified in Daphnia carinata by NMR technique (Srivastava et al., 2009). Protease activities and their class structure had been studied in Daphnia carinata (Kumar et al., 2005). SDS-PAGE showed that the molecular weight of various activity bands ranged from 16.3 to 51.1kDa.

  5. Stimulating the Immunity and Disease Resistance of Carps

    Disease outbreaks are major obstacles in successful aquaculture. Immunostimulation is one of the important areas. Achyranthes aspera has immunostimulating property. Achyranthes aspera enhances the immunity of Catla catla (Rao and Chakrabarti, 2005a), Labeo rohita (Rao et al., 2004; Rao and Chakrabarti, 2004b) and Cyprinus carpio (Rao and Chakrabarti, 2005). Achyranthes aspera increased disease resistance of Labeo rohita against bacterial infections (Rao et al., 2006).
     
  6. Effects of UV-B Radiation on Aquatic Ecosystem

    A significant reduction in stratospheric ozone has been observed over the last decade. Ozone reduction enhances the amount of ultraviolet-B radiation reaching the earth surface. The exposure to high levels of UVR can result in severe lesions of most of the exposed organs and tissues like eye and skin. Ultrastructural study of the skin, eyes and gills of various species of UV-B radiated fishes like ayu Plecoglossus altivelius, Catla catla catla showed marked changes. The exposure of the fish to the radiation resulted in the destruction of microridges in the epidermis and exposed neuromast cells of the skin. Domed protrusions were also more common in the skin of UV-B radiated fish than in the control fish. The appearance of mucus in both groups was different. In the control skin the mucus was spread over a wide area whereas in the treated fish the mucus was concentrated in a small area. The anastomozing structures of the microridges of the eyes were lost in UV-B radiated fish and the microridges themselves were fewer in number, fragmented, and aggregated. Mucus cells, prominently visible in the control fish, were distorted in the treated fish. Cell contours were irregular in UV-B radiated fish and cell to cell contacts had been lost in this group (Sharma et al., 2005, Sharma and Chakrabarti, 2006).

     
  7. Limnology

    A freshwater medusa, Limnocnida indica Annandale, 1912 was observed in a lake having free connection with the river Yamuna in Delhi. The occurrence of medusae influenced the planktonic population in the lake (Sharma and Chakrabarti, 2000). An attempt has been made to assess the impact on water quality of diverse anthropogenic activities on east and west bank of river Yamuna in Delhi, from Palla to Okhla Barrage, both biologically as well as chemically. Biological life was observed to be more affected on east bank of the river than on west bank, probably due to heavy anthropogenic influence on east bank. Favourable habitat at upstream of the barrage supports more biological life than downstream. Biomonitoring gives an overall health of the water body, which cannot be done by chemical analysis alone (Anand et al., 2002).
     
  8. Conclusions

    Recirculation technology will receive more attention as it offers opportunities for captive markets and safe applications with genetically modified organisms (GMOs) as absolute guarantees can provide to prevent escapees. This is a solution to the problem of land and water scarcity. The discharge of recirculating system water into the environment is safe. This will solve the problem of our coastal zone aquaculture. This is an eco-friendly system.

    The knowledge of lipid and digestive enzyme profiles of fish food organisms, generated in the present study may assist in the formulation of age-specific feed for fish and shellfish.

    Age-related changes in the diversity and quantity of digestive enzymes appear to represent evolutionary adaptations to the different natural diets and nutritional requirements of distinct life-history stages. All these information will help to develop a package for carp larviculture.
Recommendations for larviculture in Aquahouse
  • Aquahouse is made of polycarbonate acrylic sheet which is good for maintaining optimum temperature for survival and growth of larvae
  • Fishes reared in Aquahouse escape infection suffers less mortality and can be maintained by recirculating system.
  • Pebbles, pieces of earthen pots and hydroponics like money plant, Trapa are highly effective in reducing levels of ammonia, phosphate and COD and these are cost-effective. Hydroponics also supplements farmers net returns
  • The optimum stocking density of Indian major carps is 8,000/m3.
  • Care should be taken in feeding of carp larvae up to 15 days due to poor digestive enzyme activities.
  • Organic manures like cow dung, poultry droppings, and mustard oil cake, increase zooplankton population. vIncorporation of Achyranthes aspera in the normal feed of larvae substantially the immunity of carps against several diseases.
  • During developmental stage of the larvae the size of the foods should ranged from 100µm to 300µm.
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